Critique of Pure Reason

(Doctrine of Method)

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P 573
IF we look upon the sum of all knowledge of pure speculative
reason as an edifice for which we have at least the idea within
ourselves, it can be said that in the Transcendental Doctrine
of Elements we have made an estimate of the materials, and
have determined for what sort of edifice and for what height
and strength of building they suffice. We have found, in-
deed, that although we had contemplated building a tower
which should reach to the heavens, the supply of materials
suffices only for a dwelling-house, just sufficiently commodious
for our business on the level of experience, and just sufficiently
high to allow of our overlooking it. The bold undertaking that
we had designed is thus bound to fail through lack of material
-- not to mention the babel of tongues, which inevitably gives
rise to disputes among the workers in regard to the plan to be
followed, and which must end by scattering them over all the
world, leaving each to erect a separate building for himself,
according to his own design. At present, however, we are con-
cerned not so much with the materials as with the plan; and
inasmuch as we have been warned not to venture at random
upon a blind project which may be altogether beyond our
capacities, and yet cannot well abstain from building a secure
home for ourselves, we must plan our building in conformity
with the material which is given to us, and which is also at
the same time appropriate to our needs. 
I understand, therefore, by Transcendental Doctrine of
Method the determination of the formal conditions of a com-
plete system of pure reason. In this connection, we shall have
to treat of a discipline, a canon, an architectonic, and finally
a history of pure reason, and to provide (in its transcendental
reference) what, in relation to the use of the understanding
in general, the Schools have attempted, though very unsatis-
P 574
factorily, under the title of a practical logic. For since universal
logic is not confined to any particular kind of knowledge made
possible by the understanding (for instance, not to its pure
knowledge) and is also not confined to certain objects, it cannot,
save by borrowing knowledge from other sciences, do more
than present the titles of possible methods and the technical
terms which are used for purposes of systematisation in all
kinds of sciences; and this serves only to acquaint the novice
in advance with names the meaning and use of which he will
not learn till later. 
Owing to the general desire for knowledge, negative judg-
ments, that is, those which are such not merely as regards their
form but also as regards their content, are not held in any very
high esteem. They are regarded rather as the jealous enemies
of our unceasing endeavour to extend our knowledge, and it
almost requires an apology to win for them even tolerance, not
to say favour and high repute. 
As far as logical form is concerned, we can make negative
any proposition we like; but in respect to the content of our
knowledge in general, which is either extended or limited by
a judgment, the task peculiar to negative judgments is that of
rejecting error. Accordingly, negative propositions intended to
reject false knowledge, where yet no error is possible, are indeed
true but empty, that is, are not suited to their purpose, and
just for this reason are often quite absurd, like the proposition
of the Schoolman, that Alexander could not have conquered
any countries without an army. 
But where the limits of our possible knowledge are very
narrow, where the temptation to judge is great, where the illu-
sion that besets us is very deceptive and the harm that results
from the error is considerable, there the negative instruction,
which serves solely to guard us from errors, has even more
importance than many a piece of positive information by
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which our knowledge is increased. The compulsion, by which
the constant tendency to disobey certain rules is restrained and
finally extirpated, we entitle discipline. It is distinguished
from culture, which is intended solely to give a certain kind
of skill, and not to cancel any habitual mode of action already
present. Towards the development of a talent, which has al-
ready in itself an impulse to manifest itself, discipline will
therefore contribute in a negative, culture and doctrine in a
positive, fashion. 
That temperament and our various talents (such as imagi-
nation and wit) which incline to allow themselves a free and
unlimited activity are in many respects in need of a discipline,
everyone will readily admit. But that reason, whose proper
duty it is to prescribe a discipline for all other endeavours,
should itself stand in need of such discipline may indeed seem
strange; and it has, in fact, hitherto escaped this humiliation,
only because, in view of its stately guise and established stand-
ing, nobody could lightly come to suspect it of idly substituting
fancies for concepts, and words for things. 
There is no need of a critique of reason in its empirical em-
ployment, because in this field its principles are always sub-
ject to the test of experience. Nor is it needed in mathematics,
where the concepts of reason must be forthwith exhibited in
concreto in pure intuition, so that everything unfounded and
arbitrary in them is at once exposed. But where neither em-
pirical nor pure intuition keeps reason to a visible track, when,
that is to say, reason is being considered in its transcendental
employment, in accordance with mere concepts, it stands so
greatly in need of a discipline, to restrain its tendency towards
extension beyond the narrow limits of possible experience and
to guard it against extravagance and error, that the whole
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philosophy of pure reason has no other than this strictly
negative utility. 
P 575n
++ I am well aware that in the terminology of the Schools the title
discipline is commonly used as synonymous with instruction. How-
ever, there are so many other cases where discipline in the sense of
training by constraint is carefully distinguished from instruction in
the sense of teaching, and the very nature of things itself makes it so
imperative that we should preserve the only expressions suitable for
this distinction, that it is desirable that the former term should never
be used in any but the negative sense. 
P 576
Particular errors can be got rid of by censure,
and their causes by criticism. But where, as in the case of pure
reason, we come upon a whole system of illusions and fallacies,
intimately bound together and united under common prin-
ciples, a quite special negative legislation seems to be required,
erecting a system of precautions and self-examination under
the title of a discipline, founded on the nature of reason and
the objects of its pure employment -- a system in face of
which no pseudo-rational illusion will be able to stand, but
will at once betray itself, no matter what claims it may ad-
vance for exceptional treatment. 
 But it is well to note that in this second main division of the
transcendental Critique the discipline of pure reason is not
directed to the content but only to the method of knowledge
through pure reason. The former has already been considered
in the Doctrine of Elements. But there is so much similarity in
the mode of employing reason, whatever be the object to which
it is applied, while yet, at the same time, its transcendental
employment is so essentially different from every other, that
without the admonitory negative teaching of a discipline,
specially devised for the purpose, we cannot hope to avoid
the errors which inevitably arise from pursuing in improper
fashion methods which are indeed suitable to reason in other
fields, only not in this transcendental sphere. 
Section I
Mathematics presents the most splendid example of the suc-
cessful extension of pure reason, without the help of experience. 
Examples are contagious, especially as they quite naturally
flatter a faculty which has been successful in one field, [leading
it] to expect the same good fortune in other fields. Thus pure
reason hopes to be able to extend its domain as successfully
and securely in its transcendental as in its mathematical em-
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ployment, especially when it resorts to the same method as
has been of such obvious utility in mathematics. It is therefore
highly important for us to know whether the method of attain-
ing apodeictic certainty which is called mathematical is identi-
cal with the method by which we endeavour to obtain the
same certainty in philosophy, and which in that field would
have to be called dogmatic. 
Philosophical knowledge is the knowledge gained by reason
from concepts; mathematical knowledge is the knowledge
gained by reason from the construction of concepts. To con-
struct a concept means to exhibit a priori the intuition which
corresponds to the concept. For the construction of a concept
we therefore need a non-empirical intuition. The latter must,
as intuition, be a single object, and yet none the less, as the
construction of a concept (a universal representation), it must
in its representation express universal validity for all possible
intuitions which fall under the same concept. Thus I construct
a triangle by representing the object which corresponds to this
concept either by imagination alone, in pure intuition, or in
accordance therewith also on paper, in empirical intuition -- in
both cases completely a priori, without having borrowed the
pattern from any experience. The single figure which we draw
is empirical, and yet it serves to express the concept, without
impairing its universality. For in this empirical intuition we
consider only the act whereby we construct the concept, and
abstract from the many determinations (for instance, the mag-
nitude of the sides and of the angles), which are quite indif-
ferent, as not altering the concept 'triangle'. 
Thus philosophical knowledge considers the particular
only in the universal, mathematical knowledge the universal
in the particular, or even in the single instance, though still
always a priori and by means of reason. Accordingly, just as
this single object is determined by certain universal conditions
of construction, so the object of the concept, to which the single
object corresponds merely as its schema, must likewise be
thought as universally determined. 
The essential difference between these two kinds of know-
ledge through reason consists therefore in this formal differ-
ence, and does not depend on difference of their material or
objects. Those who propose to distinguish philosophy from
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mathematics by saying that the former has as its object quality
only and the latter quantity only, have mistaken the effect for
the cause. The form of mathematical knowledge is the cause
why it is limited exclusively to quantities. For it is the concept
of quantities only that allows of being constructed, that is, ex-
hibited a priori in intuition; whereas qualities cannot be pre-
sented in any intuition that is not empirical. Consequently
reason can obtain a knowledge of qualities only through con-
cepts. No one can obtain an intuition corresponding to the con-
cept of reality otherwise than from experience; we can never
come into possession of it a priori out of our own resources,
and prior to the empirical consciousness of reality. The shape
of a cone we can form for ourselves in intuition, unassisted by
any experience, according to its concept alone, but the colour
of this cone must be previously given in some experience or
other. I cannot represent in intuition the concept of a cause
in general except in an example supplied by experience; and
similarly with other concepts. Philosophy, as well as mathe-
matics, does indeed treat of quantities, for instance, of totality,
infinity, etc. Mathematics also concerns itself with qualities,
for instance, the difference between lines and surfaces, as
spaces of different quality, and with the continuity of extension
as one of its qualities. But although in such cases they have a
common object, the mode in which reason handles that object
is wholly different in philosophy and in mathematics. Philo-
sophy confines itself to universal concepts; mathematics can
achieve nothing by concepts alone but hastens at once to intui-
tion, in which it considers the concept in concreto, though not
empirically, but only in an intuition which it presents a priori,
that is, which it has constructed, and in which whatever follows
from the universal conditions of the construction must be uni-
versally valid of the object of the concept thus constructed. 
Suppose a philosopher be given the concept of a triangle
and he be left to find out, in his own way, what relation the
sum of its angles bears to a right angle. He has nothing
but the concept of a figure enclosed by three straight lines,
and possessing three angles. However long he meditates on
this concept, he will never produce anything new. He can
analyse and clarify the concept of a straight line or of an angle
or of the number three, but he can never arrive at any proper-
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ties not already contained in these concepts. Now let the geo-
metrician take up these questions. He at once begins by con-
structing a triangle. Since he knows that the sum of two right
angles is exactly equal to the sum of all the adjacent angles
which can be constructed from a single point on a straight line,
he prolongs one side of his triangle and obtains two adjacent
angles, which together are equal to two right angles. He then
divides the external angle by drawing a line parallel to the
opposite side of the triangle, and observes that he has thus ob-
tained an external adjacent angle which is equal to an internal
angle -- and so on. In this fashion, through a chain of in-
ferences guided throughout by intuition, he arrives at a full
evident and universally valid solution of the problem. 
But mathematics does not only construct magnitudes
(quanta) as in geometry; it also constructs magnitude as such
(quantitas), as in algebra. In this it abstracts completely from
the properties of the object that is to be thought in terms of
such a concept of magnitude. It then chooses a certain nota-
tion for all constructions of magnitude as such (numbers),
that is, for addition, subtraction, extraction of roots, etc. Once
it has adopted a notation for the general concept of magni-
tudes so far as their different relations are concerned, it ex-
hibits in intuition, in accordance with certain universal rules,
all the various operations through which the magnitudes are
produced and modified. When, for instance, one magnitude is
to be divided by another, their symbols are placed together, in
accordance with the sign for division, and similarly in the other
processes; and thus in algebra by means of a symbolic construc-
tion, just as in geometry by means of an ostensive construction
(the geometrical construction of the objects themselves), we
succeed in arriving at results which discursive knowledge
could never have reached by means of mere concepts. 
Now what can be the reason of this radical difference in
the fortunes of the philosopher and the mathematician, both
of whom practise the art of reason, the one making his way by
means of concepts, the other by means of intuitions which he
exhibits a priori in accordance with concepts? The cause is
evident from what has been said above, in our exposition of the
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fundamental transcendental doctrines. We are not here con-
cerned with analytic propositions, which can be produced by
mere analysis of concepts (in this the philosopher would
certainly have the advantage over his rival), but with syn-
thetic propositions, and indeed with just those synthetic
propositions that can be known a priori. For I must not
restrict my attention to what I am actually thinking in my
concept of a triangle (this is nothing more than the mere
definition); I must pass beyond it to properties which are
not contained in this concept, but yet belong to it. Now
this is impossible unless I determine my object in accord-
ance with the conditions either of empirical or of pure
intuition. The former would only give us an empirical pro-
position (based on the measurement of the angles), which
would not have universality, still less necessity; and so would
not at all serve our purpose. The second method of procedure
is the mathematical one, and in this case is the method of geo-
metrical construction, by means of which I combine in a pure
intuition (just as I do in empirical intuition) the manifold
which belongs to the schema of a triangle in general, and
therefore to its concept. It is by this method that universal
synthetic propositions must be constructed. 
It would therefore be quite futile for me to philosophise
upon the triangle, that is, to think about it discursively. I
should not be able to advance a single step beyond the mere
definition, which was what I had to begin with. There is indeed
a transcendental synthesis [framed] from concepts alone, a
synthesis with which the philosopher is alone competent to
deal; but it relates only to a thing in general, as defining the
conditions under which the perception of it can belong to
possible experience. But in mathematical problems there is
no question of this, nor indeed of existence at all, but only of
the properties of the objects in themselves, [that is to say],
solely in so far as these properties are connected with the con-
cept of the objects. 
In the above example we have endeavoured only to make
clear the great difference which exists between the discursive
employment of reason in accordance with concepts and its
intuitive employment by means of the construction of concepts. 
This naturally leads on to the question, what can be the cause
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which necessitates such a twofold employment of reason, and
how we are to recognise whether it is the first or the second
method that is being employed. 
All our knowledge relates, finally, to possible intuitions,
for it is through them alone that an object is given. Now an a -
priori concept, that is, a concept which is not empirical, either
already includes in itself a pure intuition (and if so, it can
be constructed), or it includes nothing but the synthesis of
possible intuitions which are not given a priori. In this latter
case we can indeed make use of it in forming synthetic a -
priori judgments, but only discursively in accordance with
concepts, never intuitively through the construction of the
The only intuition that is given a priori is that of the mere
form of appearances, space and time. A concept of space and
time, as quanta, can be exhibited a priori in intuition, that is,
constructed, either in respect of the quality (figure) of the
quanta, or through number in their quantity only (the mere
synthesis of the homogeneous manifold). But the matter of
appearances, by which things are given us in space and time,
can only be represented in perception, and therefore a poste-
riori. The only concept which represents a priori this empirical
content of appearances is the concept of a thing in general,
and the a priori synthetic knowledge of this thing in general
can give us nothing more than the mere rule of the synthesis
of that which perception may give a posteriori. It can never
yield an a priori intuition of the real object, since this must
necessarily be empirical. 
Synthetic propositions in regard to things in general, the
intuition of which does not admit of being given a priori, are
transcendental. Transcendental propositions can never be
given through construction of concepts, but only in accordance
with concepts that are a priori. They contain nothing but the
rule according to which we are to seek empirically for a certain
synthetic unity of that which is incapable of intuitive repre-
sentation a priori (that is, of perceptions). But these synthetic
principles cannot exhibit a priori any one of their concepts
in a specific instance; they can only do this a posteriori, by
means of experience, which itself is possible only in con-
formity with these principles. 
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If we are to judge synthetically in regard to a concept,
we must go beyond this concept and appeal to the intui-
tion in which it is given. For should we confine ourselves to
what is contained in the concept, the judgment would be
merely analytic, serving only as an explanation of the thought,
in terms of what is actually contained in it. But I can pass
from the concept to the corresponding pure or empirical in-
tuition, in order to consider it in that intuition in concreto,
and so to know, either a priori or a posteriori, what are the
properties of the object of the concept. The a priori method
gives us our rational and mathematical knowledge through
the construction of the concept, the a posteriori method our
merely empirical (mechanical) knowledge, which is incapable
of yielding necessary and apodeictic propositions. Thus I might
analyse my empirical concept of gold without gaining anything
more than merely an enumeration of everything that I actually
think in using the word, thus improving the logical character
of my knowledge but not in any way adding to it. But I take
the material body, familiarly known by this name, and obtain
perceptions by means of it; and these perceptions yield various
propositions which are synthetic but empirical. When the con-
cept is mathematical, as in the concept of a triangle, I am in a
position to construct the concept, that is, to give it a priori in
intuition, and in this way to obtain knowledge which is at once
synthetic and rational. But if what is given me is the transcend-
ental concept of a reality, substance, force, etc. , it indicates
neither an empirical nor a pure intuition, but only the synthesis
of empirical intuitions, which, as being empirical, cannot be
given a priori. And since the synthesis is thus unable to ad-
vance a priori, beyond the concept, to the corresponding in-
tuition, the concept cannot yield any determining synthetic
proposition, but only a principle of the synthesis of possible empirical intuiti
++ With the concept of cause I do really go beyond the empirical
concept of an event (something happening), yet I do not pass to the
intuition which exhibits the concept of cause in concreto, but to the
time-conditions in general, which in experience may be found to be
in accord with this concept. I therefore proceed merely
with concepts; I cannot proceed by means of the construction of
concepts, since the concept is a rule of the synthesis of percep-
tions, and the latter are not pure intuitions, and so do not permit of
being given a priori. 
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A transcendental proposition is therefore
synthetic knowledge through reason, in accordance with mere
concepts; and it is discursive, in that while it is what alone
makes possible any synthetic unity of empirical knowledge, it
yet gives us no intuition a priori. 
There is thus a twofold employment of reason; and while
the two modes of employment resemble each other in the uni-
versality and a priori origin of their knowledge, in outcome
they are very different. The reason is that in the [field of]
appearance, in terms of which all objects are given us,
there are two elements, the form of intuition (space and time),
which can be known and determined completely a priori, and
the matter (the physical element) or content -- the latter signi-
fying something which is met with in space and time and which
therefore contains an existent corresponding to sensation. 
In respect to this material element, which can never be given
in any determinate fashion otherwise than empirically, we can
have nothing a priori except indeterminate concepts of the syn-
thesis of possible sensations, in so far as they belong, in a pos-
sible experience, to the unity of apperception. As regards the
formal element, we can determine our concepts in a priori
intuition, inasmuch as we create for ourselves, in space and
time, through a homogeneous synthesis, the objects themselves
-- these objects being viewed simply as quanta. The former
method is called the employment of reason in accordance with
concepts; in so employing it we can do nothing more than bring
appearances under concepts, according to their actual content. 
The concepts cannot be made determinate in this manner,
save only empirically, that is, a posteriori (although always in
accordance with these concepts as rules of an empirical syn-
thesis). The other method is the employment of reason through
the construction of concepts; and since the concepts here re-
late to an a priori intuition, they are for this very reason them-
selves a priori and can be given in a quite determinate fashion
in pure intuition, without the help of any empirical data. The
consideration of everything which exists in space or time, in
regard to the questions, whether and how far it is a quantum
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or not, whether we are to ascribe to it positive being or the ab-
sence of such, how far this something occupying space or time
is a primary substratum or a mere determination [of substance],
whether there be a relation of its existence to some other ex-
istence, as cause or effect, and finally in respect of its existence
whether it is isolated or is in reciprocal relation to and depend-
ence upon others -- these questions, as also the question of the
possibility of this existence, its actuality and necessity, or the
opposites of these, one and all belong altogether to knowledge
obtained by reason from concepts, such knowledge being
termed philosophical. But the determination of an intuition a -
priori in space (figure), the division of time (duration), or even
just the knowledge of the universal element in the synthesis of
one and the same thing in time and space, and the magnitude
of an intuition that is thereby generated (number), -- all this is
the work of reason through construction of concepts, and is
called mathematical. 
The great success which attends reason in its mathematical
employment quite naturally gives rise to the expectation that
it, or at any rate its method, will have the same success in other
fields as in that of quantity. For this method has the advantage
of being able to realise all its concepts in intuitions, which it
can provide a priori, and by which it becomes, so to speak,
master of nature; whereas pure philosophy is all at sea when it
seeks through a priori discursive concepts to obtain insight in
regard to the natural world, being unable to intuit a priori
(and thereby to confirm) their reality. Nor does there seem
to be, on the part of the experts in mathematics, any lack
of self-confidence as to this procedure -- or on the part of the
vulgar of great expectations from their skill -- should they
apply themselves to carry out their project. For, since they
have hardly ever attempted to philosophise in regard to their
mathematics (a hard task! ), the specific difference between the
two employments of reason has never so much as occurred to
them. Current, empirical rules, which they borrow from ordin-
ary consciousness, they treat as being axiomatic. In the ques-
tion as to the source of the concepts of space and time they are
not in the least interested, although it is precisely with these
concepts (as the only original quanta) that they are themselves
occupied. Similarly, they think it unnecessary to investigate
P 585
the origin of the pure concepts of understanding and in so
doing to determine the extent of their validity; they care only
to make use of them. In all this they are entirely in the right,
provided only they do not overstep the proper limits, that is,
the limits of the natural world. But, unconsciously, they pass
from the field of sensibility to the precarious ground of pure and
even transcendental concepts, a ground (instabilis tellus, in-
nabilis unda) that permits them neither to stand nor to swim, and
where their hasty tracks are soon obliterated. In mathematics,
on the other hand, their passage gives rise to a broad highway,
which the latest posterity may still tread with confidence. 
We have made it our duty to determine, with exactitude
and certainty, the limits of pure reason in its transcendental
employment. But the pursuit of such transcendental know-
ledge has this peculiarity, that in spite of the plainest and most
urgent warnings men still allow themselves to be deluded by
false hopes, and therefore to postpone the total abandonment
of all proposed attempts to advance beyond the bounds of ex-
perience into the enticing regions of the intellectual world. It
therefore becomes necessary to cut away the last anchor of
these fantastic hopes, that is, to show that the pursuit of the
mathematical method cannot be of the least advantage in this
kind of knowledge (unless it be in exhibiting more plainly
the limitations of the method); and that mathematics and
philosophy, although in natural science they do, indeed, go
hand in hand, are none the less so completely different, that
the procedure of the one can never be imitated by the other. 
The exactness of mathematics rests upon definitions, axioms
and demonstrations. I shall content myself with showing that
none of these, in the sense in which they are understood by the
mathematician, can be achieved or imitated by the philosopher. 
I shall show that in philosophy the geometrician can by his
method build only so many houses of cards, just as in mathe-
matics the employment of a philosophical method results only
in mere talk. Indeed it is precisely in knowing its limits that
philosophy consists; and even the mathematician, unless his
talent is of such a specialised character that it naturally confines
itself to its proper field, cannot afford to ignore the warnings
of philosophy, or to behave as if he were superior to them. 
P 586
1. Definitions. -- To define, as the word itself indicates,
really only means to present the complete, original concept of
a thing within the limits of its concept. If this be our standard,
an empirical concept cannot be defined at all, but only made
explicit. For since we find in it only a few characteristics of a
certain species of sensible object, it is never certain that we
are not using the word, in denoting one and the same object,
sometimes so as to stand for more, and sometimes so as to
stand for fewer characteristics. Thus in the concept of gold
one man may think, in addition to its weight, colour, malle-
ability, also its property of resisting rust, while another will
perhaps know nothing of this quality. We make use of certain
characteristics only so long as they are adequate for the pur-
pose of making distinctions; new observations remove some
properties and add others; and thus the limits of the concept
are never assured. And indeed what useful purpose could be
served by defining an empirical concept, such, for instance, as
that of water? When we speak of water and its properties, we
do not stop short at what is thought in the word, water, but
proceed to experiments. The word, with the few characteristics
which we attach to it, is more properly to be regarded as
merely a designation than as a concept of the thing; the so-
called definition is nothing more than a determining of the
word. In the second place, it is also true that no concept given
a priori, such as substance, cause, right, equity, etc. , can,
strictly speaking, be defined. For I can never be certain that
the clear representation of a given concept, which as given may
still be confused, has been completely effected, unless I know that
it is adequate to its object. But since the concept of it may, as
given, include many obscure representations, which we over-
look in our analysis, although we are constantly making use of
them in our application of the concept, the completeness of the
analysis of my concept is always in doubt, and a multiplicity
P 587
of suitable examples suffices only to make the completeness
probable, never to make it apodeictically certain. 
P 586n
++ Completeness means clearness and sufficiency of character-
istics; by limits is meant the precision shown in there not being more
of these characteristics than belong to the complete concept; by
original is meant that this determination of these limits is not
derived from anything else, and therefore does not require any proof;
for if it did, that would disqualify the supposed explanation from
standing at the head of all the judgments regarding its object. 
P 587
Instead of the
term, definition, I prefer to use the term, exposition, as being a
more guarded term, which the critic can accept as being up to
a certain point valid, though still entertaining doubts as to the
completeness of the analysis. Since, then, neither empirical con-
cepts nor concepts given a priori allow of definition, the only
remaining kind of concepts, upon which this mental operation
can be tried, are arbitrarily invented concepts. A concept which
I have invented I can always define; for since it is not given to
me either by the nature of understanding or by experience, but
is such as I have myself deliberately made it to be, I must know
what I have intended to think in using it. I cannot, however,
say that I have thereby defined a true object. For if the concept
depends on empirical conditions, as e.g. the concept of a ship's
clock, this arbitrary concept of mine does not assure me of the
existence or of the possibility of its object. I do not even know
from it whether it has an object at all, and my explanation
may better be described as a declaration of my project than
as a definition of an object. There remain, therefore, no
concepts which allow of definition, except only those which
contain an arbitrary synthesis that admits of a priori construc-
tion. Consequently, mathematics is the only science that has
definitions. For the object which it thinks it exhibits a priori in
intuition, and this object certainly cannot contain either more
or less than the concept, since it is through the definition that
the concept of the object is given -- and given originally, that
is, without its being necessary to derive the definition from
any other source. The German language has for the [Latin]
terms exposition, explication, declaration, and definition only
one word, Erklarung, and we need not, therefore, be so
stringent in our requirements as altogether to refuse to philo-
sophical explanations the honourable title, definition. We
shall confine ourselves simply to remarking that while philo-
sophical definitions are never more than expositions of given
concepts, mathematical definitions are constructions of con-
P 588
cepts, originally framed by the mind itself; and that while the
former can be obtained only by analysis (the completeness of
which is never apodeictically certain), the latter are produced
synthetically. Whereas, therefore, mathematical definitions
make their concepts, in philosophical definitions concepts are
only explained. From this it follows:
(a) That in philosophy we must not imitate mathematics
by beginning with definitions, unless it be by way simply of
experiment. For since the definitions are analyses of given
concepts, they presuppose the prior presence of the concepts,
although in a confused state; and the incomplete exposition
must precede the complete. Consequently, we can infer a good
deal from a few characteristics, derived from an incomplete
analysis, without having yet reached the complete exposition,
that is, the definition. In short,the definition in all its precision
and clarity ought, in philosophy, to come rather at the end
than at the beginning of our enquiries. In mathematics, on
the other hand, we have no concept whatsoever prior to the
definition, through which the concept itself is first given. For
this reason mathematical science must always begin, and it can
always begin, with the definition. 
(b) That mathematical definitions can never be in error. 
For since the concept is first given through the definition, it
includes nothing except precisely what the definition intends
should be understood by it. But although nothing incorrect can
be introduced into its content, there may sometimes, though
rarely, be a defect in the form in which it is clothed, namely as
regards precision. 
++ Philosophy is full of faulty definitions, especially of definitions
which, while indeed containing some of the elements required, are
yet not complete. If we could make no use of a concept till we
had defined it, all philosophy would be in a pitiable plight. But
since a good and safe use can still be made of the elements obtained
by analysis so far as they go, defective definitions, that is, propositions
which are properly not definitions, but are yet true, and are therefore
approximations to definitions, can be employed with great advantage. 
In mathematics definition belongs ad esse, in philosophy ad melius
esse. It is desirable to attain an adequate definition, but often very
difficult. The jurists are still without a definition of their concept of
P 588
Thus the common explanation of the circle
that it is a curved line every point in which is equidistant
P 589
from one and the same point (the centre), has the defect that
the determination, curved, is introduced unnecessarily. For
there must be a particular theorem, deduced from the de-
finition and easily capable of proof, namely, that if all points
in a line are equidistant from one and the same point, the line
is curved (no part of it straight). Analytic definitions, on the
other hand, may err in many ways, either through introducing
characteristics which do not really belong to the concept, or by
lacking that completeness which is the essential feature of a
definition. The latter defect is due to the fact that we can never
be quite certain of the completeness of the analysis. For these
reasons the mathematical method of definition does not admit
of imitation in philosophy. 
2. Axioms. -- These, in so far as they are immediately
certain, are synthetic a priori principles. Now one concept
cannot be combined with another synthetically and also at the
same time immediately, since, to be able to pass beyond either
concept, a third something is required to mediate our know-
ledge. Accordingly, since philosophy is simply what reason
knows by means of concepts, no principle deserving the name
of an axiom is to be found in it. Mathematics, on the other
hand, can have axioms, since by means of the construction of
concepts in the intuition of the object it can combine the pre-
dicates of the object both a priori and immediately, as, for
instance, in the proposition that three points always lie in a
plane. But a synthetic principle derived from concepts alone
can never be immediately certain, for instance, the proposition
that everything which happens has a cause. Here I must look
round for a third something, namely, the condition of time-
determination in an experience; I cannot obtain knowledge of
such a principle directly and immediately from the concepts
alone. Discursive principles are therefore quite different from
intuitive principles, that is, from axioms; and always require
a deduction. Axioms, on the other hand, require no such de-
duction, and for the same reason are evident -- a claim which
the philosophical principles can never advance, however great
their certainty. Consequently, the synthetic propositions of pure,
transcendental reason are, one and all, infinitely removed from
being as evident -- which is yet so often arrogantly claimed
on their behalf -- as the proposition that twice two make four. 
P 590
In the Analytic I have indeed introduced some axioms of in-
tuition into the table of the principles of pure understanding;
but the principle there applied is not itself an axiom, but
serves only to specify the principle of the possibility of axioms
in general, and is itself no more than a principle derived from
concepts. For the possibility of mathematics must itself be
demonstrated in transcendental philosophy. Philosophy has
therefore no axioms, and may never prescribe its a priori
principles in any such absolute manner, but must resign itself
to establishing its authority in their regard by a thorough
3. Demonstrations. -- An apodeictic proof can be called a
demonstration, only in so far as it is intuitive. Experience
teaches us what is, but does not teach us that it could not
be other than what it is. Consequently, no empirical grounds
of proof can ever amount to apodeictic proof. Even from a -
priori concepts, as employed in discursive knowledge, there
can never arise intuitive certainty, that is, [demonstrative]
evidence, however apodeictically certain the judgment may
otherwise be. Mathematics alone, therefore, contains demon-
strations, since it derives its knowledge not from concepts
but from the construction of them, that is, from intuition,
which can be given a priori in accordance with the concepts. 
Even the method of algebra with its equations, from which
the correct answer, together with its proof, is deduced by re-
duction, is not indeed geometrical in nature, but is still con-
structive in a way characteristic of the science. The concepts
attached to the symbols, especially concerning the relations
of magnitudes, are presented in intuition; and this method,
in addition to its heuristic advantages, secures all inferences
against error by setting each one before our eyes. While
philosophical knowledge must do without this advantage,
inasmuch as it has always to consider the universal in
abstracto (by means of concepts), mathematics can consider
the universal in concreto (in the single intuition) and yet at the
same time through pure a priori representation, whereby all
errors are at once made evident. I should therefore prefer to
P 591
call the first kind acroamatic (discursive) proofs, since they
may be conducted by the agency of words alone (the object
in thought), rather than demonstrations which, as the term
itself indicates, proceed in and through the intuition of the
From all this it follows that it is not in keeping with the
nature of philosophy, especially in the field of pure reason, to
take pride in a dogmatic procedure, and to deck itself out with
the title and insignia of mathematics, to whose ranks it does
not belong, though it has every ground to hope for a sisterly
union with it. Such pretensions are idle claims which can never
be satisfied, and indeed must divert philosophy from its true
purpose, namely, to expose the illusions of a reason that forgets
its limits, and by sufficiently clarifying our concepts to recall
it from its presumptuous speculative pursuits to modest but
thorough self-knowledge. Reason must not, therefore, in its
transcendental endeavours, hasten forward with sanguine
expectations, as though the path which it has traversed led
directly to the goal, and as though the accepted premisses
could be so securely relied upon that there can be no need of
constantly returning to them and of considering whether we
may not perhaps, in the course of the inferences, discover de-
fects which have been overlooked in the principles, and which
render it necessary either to determine these principles more
fully or to change them entirely. 
I divide all apodeictic propositions, whether demonstrable
or immediately certain, into dogmata and mathemata. A syn-
thetic proposition directly derived from concepts is a dogma;
a synthetic proposition, when directly obtained through the
construction of concepts, is a mathema. Analytic judgments
really teach us nothing more about the object than what the
concept which we have of it already contains; they do not
extend our knowledge beyond the concept of the object, but
only clarify the concept. They cannot therefore rightly be
called dogmas (a word which might perhaps be translated
doctrines). Of the two kinds of synthetic a priori propositions
only those belonging to philosophical knowledge can, accord-
ing to the ordinary usage of words, be entitled dogmas; the
propositions of arithmetic or geometry would hardly be so
P 592
named. The customary use of words thus confirms our in-
terpretation of the term, namely, that only judgments derived
from concepts can be called dogmatic, not those based on the
construction of concepts. 
Now in the whole domain of pure reason, in its merely
speculative employment, there is not to be found a single
synthetic judgment directly derived from concepts. For, as we
have shown, ideas cannot form the basis of any objectively
valid synthetic judgment. Through concepts of understanding
pure reason does, indeed, establish secure principles, not how-
ever directly from concepts alone, but always only indirectly
through relation of these concepts to something altogether con-
tingent, namely, possible experience. When such experience
(that is, something as object of possible experiences) is pre-
supposed, these principles are indeed apodeictically certain;
but in themselves, directly, they can never be known a priori. 
Thus no one can acquire insight into the proposition that
everything which happens has its cause, merely from the con-
cepts involved. It is not, therefore, a dogma, although from
another point of view, namely, from that of the sole field of
its possible employment, that is, experience, it can be proved
with complete apodeictic certainty. But though it needs proof,
it should be entitled a principle, not a theorem, because it has
the peculiar character that it makes possible the very experi-
ence which is its own ground of proof, and that in this ex-
perience it must always itself be presupposed. 
Now if in the speculative employment of pure reason there
are no dogmas, to serve as its special subject-matter, all
dogmatic methods, whether borrowed from the mathematician
or specially invented, are as such inappropriate. For they only
serve to conceal defects and errors, and to mislead philosophy,
whose true purpose is to present every step of reason in the
clearest light. Nevertheless its method can always be system-
atic. For our reason is itself, subjectively, a system, though in
its pure employment, by means of mere concepts, it is no more
than a system whereby our investigations can be conducted
in accordance with principles of unity, the material being pro-
vided by experience alone. We cannot here discuss the method
peculiar to transcendental philosophy; we are at present con-
P 593
cerned only with a critical estimate of what may be expected
from our faculties -- whether we are in a position to build at all;
and to what height, with the material at our disposal (the pure
a priori concepts), we may hope to carry the edifice. 
Section 2
Reason must in all its undertakings subject itself to criti-
cism; should it limit freedom of criticism by any prohibi-
tions, it must harm itself, drawing upon itself a damaging
suspicion. Nothing is so important through its usefulness,
nothing so sacred, that it may be exempted from this search-
ing examination, which knows no respect for persons. Reason
depends on this freedom for its very existence. For reason
has no dictatorial authority; its verdict is always simply the
agreement of free citizens, of whom each one must be permitted
to express, without let or hindrance, his objections or even his
But while reason can never refuse to submit to criticism,
it does not always have cause to fear it. In its dogmatic (non-
mathematical) employment it is not, indeed, so thoroughly
conscious of such exact observation of its own supreme laws,
as not to feel constrained to present itself with diffidence, nay,
with entire renunciation of all assumed dogmatic authority,
to the critical scrutiny of a higher judicial reason. 
The situation is, however, quite otherwise, when reason
has to deal not with the verdict of a judge, but with the claims
of a fellow-citizen, and against these has only to act in self-
defence. For since these are intended to be just as dogmatic
in denial as its own are in affirmation, it is able to justify itself
kat' anthropon, in a manner which ensures it against all inter-
ference, and provides it with a title to secure possession that
need fear no outside claims, although kat' alytheian the title
cannot itself be conclusively proved. 
By the polemical employment of pure reason I mean the
P 594
defence of its propositions as against the dogmatic counter-
propositions through which they are denied. Here the conten-
tion is not that its own assertions may not, perhaps, be false,
but only that no one can assert the opposite with apodeictic
certainty, or even, indeed, with a greater degree of likelihood. 
We do not here hold our possessions upon sufferance; for
although our title to them may not be satisfactory, it is yet
quite certain that no one can ever be in a position to prove the
illegality of the title. 
It is grievous, indeed, and disheartening, that there should
be any such thing as an antithetic of pure reason, and that
reason, which is the highest tribunal for all conflicts, should
thus be at variance with itself. We had to deal, in a previous
chapter, with such an antithetic; but it turned out to be only
an apparent conflict, resting upon a misunderstanding. In ac-
cordance with the common prejudice, it took appearances as
being things in themselves, and then required an absolute
completeness of their synthesis in the one mode or in the other
(this being equally impossible in either way) -- a demand which
is not at all permissible in respect of appearances. There was,
therefore, no real self-contradiction of reason in the propound-
ing of the two propositions, that the series of appearances given
in themselves has an absolutely first beginning, and that this
series is absolutely and in itself without any beginning. For
the two propositions are quite consistent with each other, inas-
much as appearances, in respect of their existence (as appear-
ances), are in themselves nothing at all, that is, [so regarded]
are something self-contradictory; for the assumption [that
they do thus exist in themselves] must naturally lead to self-
contradictory inferences. 
 But there are other cases in which we cannot allege any
such misunderstanding, and in which we cannot, therefore,
dispose of the conflict of reason in the above manner -- when,
for instance, it is asserted, on the one hand, theistically, that
there is a supreme being, and on the other hand, atheistically,
that there is no supreme being; or as in psychology, that every-
thing which thinks is endowed with absolute and abiding unity
and is therefore distinct from all transitory material unity,
and, in opposition thereto, that the soul is not immaterial unity
P 595
and cannot be exempt from transitoriness. For since in these
cases the understanding has to deal only with things in them-
selves and not with appearances, the object of such questions
is free from any foreign element that is in contradiction with
its nature. There would indeed be a real conflict, if pure reason
had anything to say on the negative side which amounted to
a positive ground for its negative contentions. For so far as
concerns criticism of the grounds of proof offered by those
who make dogmatic affirmations, the criticism can be freely
admitted, without our having on that account to give up these
affirmations, which have at least the interest of reason in
their favour -- an interest to which the opposite party cannot
I do not at all share the opinion which certain excel-
lent and thoughtful men (such as Sulzer), in face of the
weakness of the arguments hitherto employed, have so often
been led to express, that we may hope sometime to discover
conclusive demonstrations of the two cardinal propositions of
our reason -- that there is a God, and that there is a future life. 
On the contrary, I am certain that this will never happen. For
whence will reason obtain ground for such synthetic assertions,
which do not relate to objects of experience and their inner
possibility. But it is also apodeictically certain that there will
never be anyone who will be able to assert the opposite with
the least show [of proof], much less, dogmatically. For since he
could prove this only through pure reason, he must undertake
to prove that a supreme being, and the thinking subject in
us [viewed] as pure intelligence, are impossible. But whence
will he obtain the modes of knowledge which could justify
him in thus judging synthetically in regard to things that lie
beyond all possible experience. We may therefore be so com-
pletely assured that no one will ever prove the opposite, that
there is no need for us to concern ourselves with formal argu-
ments. We are always in a position to accept these propositions
-- propositions which are so very closely bound up with the
speculative interest of our reason in its empirical employment,
and which, moreover, are the sole means of reconciling the
P 596
speculative with the practical interest. As against our opponent
who must not be considered here as a critic only, we are equipped
with our non liquet, which cannot fail to disconcert him. At
the same time we do not mind his turning this argument
upon ourselves, since we always have in reserve the subjective
maxim of reason, which is necessarily lacking to our opponent,
and under its protection can look upon all his vain attacks with
a tranquil indifference. 
There is thus no real antithetic of pure reason. For the
arena for such an antithetic would have to be located in the
domain of pure theology and psychology; and in that domain
no combatant can be adequately equipped, or have weapons
that we need fear. Ridicule and boasting form his whole
armoury, and these can be laughed at, as mere child's play. 
This is a comforting consideration, and affords reason fresh
courage; for upon what could it rely, if, while it alone is called
upon to remove all errors, it should yet be at variance with
itself, and without hope of peace and quiet possession. 
 Everything which nature has itself instituted is good for
some purpose. Even poisons have their use. They serve to
counteract other poisons generated in our bodily humours,
and must have a place in every complete pharmacopoeia. The
objections against the persuasions and complacency of our
purely speculative reason arise from the very nature of reason
itself, and must therefore have their own good use and purpose,
which ought not to be disdained. Why has Providence placed
many things which are closely bound up with our highest in-
terests so far beyond our reach that we are only permitted to
apprehend them in a manner lacking in clearness and subject
to doubt -- in such fashion that our enquiring gaze is more ex-
cited than satisfied? We may, indeed, be in doubt whether it
serves any useful purpose, and whether it is not perhaps even
harmful, to venture upon bold utterances in regard to such
uncertain matters. But there can be no manner of doubt that
it is always best to grant reason complete liberty, both of
enquiry and of criticism, so that it may not be hindered in
attending to its own proper interests. These interests are no
less furthered by the limitation than by the extension of its
speculations, and will always suffer when outside influences
P 597
intervene to divert it from its proper path, and to constrain
it by what is irrelevant to its own proper ends. 
Allow, therefore, your opponent to speak in the name of
reason, and combat him only with weapons of reason. For the
rest, have no anxiety as to the outcome in its bearing upon
our practical interests, since in a merely speculative dispute
they are never in any way affected. The conflict serves only to
disclose a certain antinomy of reason which, inasmuch as it
is due to the very nature of reason, must receive a hearing
and be scrutinised. Reason is benefited by the consideration
of its object from both sides, and its judgment is corrected in
being thus limited. What is here in dispute is not the practical
interests of reason but the mode of their presentation. For
although we have to surrender the language of knowledge,
we still have sufficient ground to employ, in the presence of
the most exacting reason, the quite legitimate language of a
firm faith. 
If we should ask the dispassionate David Hume, [by
temperament] so peculiarly fitted for balanced judgment,
what led him to undermine, through far-fetched subtleties
so elaborately thought out, the conviction which is so com-
forting and beneficial for mankind, that their reason has
sufficient insight for the assertion and for the determinate
conception of a supreme being, he would answer: 'Solely in
order to advance reason in its self-knowledge, and because of
a certain indignation at the violence that is done to reason by
those who, while boasting of its powers, yet hinder it from
candid admission of the weaknesses which have become ob-
vious to it through its own self-examination'. If, on the other
hand, we should ask Priestley, who was wholly devoted to the
empirical employment of reason and out of sympathy with
all transcendent speculation, what motives had induced him --
himself a pious and zealous teacher of religion -- to pull down
two such pillars of all religion as the freedom and immortality
of the soul (the hope of a future life is for him only the expecta-
tion of the miracle of resurrection), he would not be able to give
P 598
any other answer than that he was concerned for the interest
of reason, which must suffer when we seek to exempt certain
objects from the laws of material nature, the only laws which
we can know and determine with exactitude. It would be
unjust to decry the latter (who knew how to combine his para-
doxical teaching with the interests of religion), and so to give
pain to a well-intentioned man, simply because he is unable
to find his bearings, having strayed outside the field of natural
science. And the same favour must be accorded to the no
less well disposed and in his moral character quite blameless
Hume, when he insists upon the relevance, in this field, of
his subtly thought-out speculations. For, as he rightly held,
their object lies entirely outside the limits of natural science,
in the domain of pure ideas. 
What, then, is to be done, especially in view of the danger
which would thus seem to threaten the best interests of man-
kind? Nothing is more natural, nothing is more reasonable,
than the decision which we are hereby called upon to make. 
Leave such thinkers free to take their own line. If they exhibit
talent, if they initiate new and profound enquiries, in a word,
if they show reason, reason always stands to gain. If we resort to
other means than those of untrammelled reason, if we raise the
cry of high treason, and act as if we were summoning the vulgar
to extinguish a conflagration -- the vulgar who have no under-
standing of such subtle enquiries -- we make ourselves ridicu-
lous. For the question at issue is not as to what, in these enquiries,
is beneficial or detrimental to the best interests of mankind,
but only how far reason can advance by means of speculation
that abstracts from all interests, and whether such speculation
can count for anything, or must not rather be given up in ex-
change for the practical. Instead, therefore, of rushing into the
fight, sword in hand, we should rather play the part of the
peaceable onlooker, from the safe seat of the critic. The struggle
is indeed toilsome to the combatants, but for us can be enter-
taining; and its outcome -- certain to be quite bloodless -- must
be of advantage as contributing to our theoretical insight. For
it is indeed absurd to look to reason for enlightenment, and
yet to prescribe beforehand which side she must necessarily
favour. Besides, reason is already of itself so confined and held
P 599
within limits by reason, that we have no need to call out the
guard, with a view to bringing the civil power to bear upon
that party whose alarming superiority may seem to us to be
dangerous. In this dialectic no victory is gained that need give
us cause for anxiety. 
Reason does indeed stand in sore need of such dialectical
debate; and it is greatly to be wished that the debate had been
instituted sooner and with unqualified public approval. For in
that case criticism would sooner have reached a ripe maturity,
and all these disputes would of necessity at once have come to
an end, the opposing parties having learned to recognise the
illusions and prejudices which have set them at variance. 
There is in human nature a certain disingenuousness,
which, like everything that comes from nature, must finally
contribute to good ends, namely, a disposition to conceal our
real sentiments, and to make show of certain assumed senti-
ments which are regarded as good and creditable. This
tendency to conceal ourselves and to assume the appearance
of what contributes to our advantage, has, undoubtedly, not
only civilised us, but gradually, in a certain measure, moral-
ised us. For so long as we were not in a position to see
through the outward show of respectability, honesty, and
modesty, we found in the seemingly genuine examples of
goodness with which we were surrounded a school for self-
improvement. But this disposition to represent ourselves as
better than we are, and to give expression to sentiments which
we do not share, serves as a merely provisional arrangement,
to lead us from the state of savage rudeness, and to allow of
our assuming at least the outward bearing of what we know to
be good. But later, when true principles have been developed,
and have become part of our way of thought, this duplicity
must be more and more earnestly combated; otherwise it cor-
rupts the heart, and checks the growth of good sentiments
with the rank weeds of fair appearances. 
I am sorry to observe the same disingenuousness, mis-
representation, and hypocrisy even in the utterances of specu-
lative thought, where there are far fewer hindrances to our
making, as is fitting, frank and unreserved admission of our
thoughts, and no advantage whatsoever in acting otherwise. 
P 600
For what can be more prejudicial to the interests of knowledge
than to communicate even our very thoughts in a falsified
form, to conceal doubts which we feel in regard to our
own assertions, or to give an appearance of conclusiveness
to grounds of proofs which we ourselves recognise to be in-
sufficient. So long as mere personal vanity is what breeds
these secret devices -- and this is generally the case with those
speculative judgments which concern no special interest and
do not easily allow of apodeictic certainty -- it is counteracted,
in the process of enlisting general acceptance, by the vanity of
others; and thus in the end the result is the same as would have
been obtained, though much sooner, by entirely sincere and
honest procedure. When the common people are of opinion
that those who indulge in subtle questionings aim at nothing
less than to shake the very foundations of public welfare, it
may, indeed, seem not only prudent but permissible, and in-
deed even commendable, to further the good cause through so-
phistical arguments rather than allow its supposed antagonists
the advantage of having made us lower our tone to that of a
merely practical conviction, and of having compelled us to
admit our lack of speculative and apodeictic certainty. I
cannot, however, but think that nothing is so entirely incom-
patible with the purpose of maintaining a good cause as deceit,
hipocrisy and fraud. Surely the least that can be demanded
is that in a matter of pure speculation, when weighing the con-
siderations cited by reason, we should proceed in an entirely
sincere manner. If we could confidently count even upon this
little, the conflict of speculative reason regarding the im-
portant questions of God, the immortality of the soul, and
freedom, would long ago have been decided, or would very
soon be brought to a conclusion. Thus it often happens that
purity of purpose is in inverse ratio to the goodness of the
cause, and that candour and honesty are perhaps more likely
to be found among its assailants than among its defenders. 
I shall therefore assume that I have readers who do not
wish to see a righteous cause defended in an unrighteous
manner; and that they will consequently take it as agreed,
that, according to our principles of criticism, and having regard
not to what commonly happens, but to what ought to happen,
there can, properly speaking, be no polemic of pure reason. 
P 601
For how can two persons carry on a dispute about a thing the
reality of which neither of them can present in actual or even in
possible experience -- a dispute in which they brood over the
mere idea of the thing, in order to extract from it something
more than the idea, namely, the reality of the object itself? What
means have they of ending the dispute, since neither of them
can make his thesis genuinely comprehensible and certain, but
only attack and refute that of his opponent? For this is the fate
of all assertions of pure reason: that since they transcend the
conditions of all possible experience, outside which the authen-
tication of truth is in no wise possible, while at the same time
they have to make use of the laws of the understanding -- laws
which are adapted only for empirical employment, but without
which no step can be taken in synthetic thought -- neither side
can avoid exposing its weakness, and each can therefore take
advantage of the weakness of the other. 
The critique of pure reason can be regarded as the true
tribunal for all disputes of pure reason; for it is not involved
in these disputes -- disputes which are immediately concerned
with objects -- but is directed to the determining and esti-
mating of the rights of reason in general, in accordance with
the principles of their first institution. 
In the absence of this critique reason is, as it were, in the
state of nature, and can establish and secure its assertions and
claims only through war. The critique, on the other hand,
arriving at all its decisions in the light of fundamental prin-
ciples of its own institution, the authority of which no one can
question, secures to us the peace of a legal order, in which our
disputes have to be conducted solely by the recognised methods
of legal action. In the former state, the disputes are ended by
a victory to which both sides lay claim, and which is generally
followed by a merely temporary armistice, arranged by some
mediating authority; in the latter, by a judicial sentence
which, as it strikes at the very root of the conflicts, effectively
secures an eternal peace. The endless disputes of a merely
dogmatic reason thus finally constrain us to seek relief in
some critique of reason itself, and in a legislation based upon
such criticism. As Hobbes maintains, the state of nature is a
state of injustice and violence, and we have no option save to
abandon it and submit ourselves to the constraint of law, which
P 602
limits our freedom solely in order that it may be consistent
with the freedom of others and with the common good of all. 
This freedom will carry with it the right to submit openly
for discussion the thoughts and doubts with which we find our-
selves unable to deal, and to do so without being decried as
troublesome and dangerous citizens. This is one of the original
rights of human reason, which recognises no other judge than
that universal human reason in which everyone has his say. And
since all improvement of which our state is capable must be ob-
tained from this source, such a right is sacred and must not be
curtailed. Indeed we are very ill-advised in decrying as danger-
ous any bold assertions against, or audacious attacks upon,
the view which already has on its side the approval of the
largest and best portion of the community; in so doing we
are ascribing to them an importance which they are not
entitled to claim. Whenever I hear that a writer of real ability
has demonstrated away the freedom of the human will, the
hope of a future life, and the existence of God, I am eager to
read the book, for I expect him by his talents to increase my
insight into these matters. Already, before having opened it, I
am perfectly certain that he has not justified any one of his
specific claims; not because I believe that I am in possession
of conclusive proofs of these important propositions, but
because the transcendental critique, which has disclosed to
me all the resources of our pure reason, has completely con-
vinced me that, as reason is incompetent to arrive at affirmative
assertions in this field, it is equally unable, indeed even less
able, to establish any negative conclusion in regard to these
questions. For from what source will the free thinker derive his
professed knowledge that there is, for example, no supreme
being? This proposition is outside the field of possible experi-
ence, and therefore beyond the limits of all human insight. 
The reply of the dogmatic defender of the good cause I should
not read at all. I know beforehand that he will attack the
sophistical arguments of his opponent simply in order to gain
acceptance for his own; and I also know that a quite familiar
line of false argument does not yield so much material for new
observations as one that is novel and ingeniously elaborated. 
P 603
The opponent of religion is indeed, in his own way, no less
dogmatic, but he affords me a welcome opportunity of apply-
ing and, in this or that respect, amending the principles of my
Critique, while at the same time I need be in no fear of these
principles being in the least degree endangered. 
But must not the young, at least, when entrusted to our
academical teaching, be warned against such writings, and
preserved from a premature knowledge of such dangerous
propositions, until their faculty of judgment is mature, or
rather until the doctrine which we seek to instil into them has
taken such firm root, that they are able effectively to with-
stand all persuasion to contrary views, from whatever quarter
it may come? 
If we are to insist on holding to dogmatic procedure in
matters of pure reason, and on disposing of our opponents
in strictly polemical fashion, that is, by ourselves taking sides
in the controversy, and therefore equipping ourselves with
proofs in support of the opposite assertions, certainly this
procedure would for the time being be the most expedient; but
in the long run nothing would be more foolish and ineffective
than to keep youthful reason thus for a period under tutelage. 
This will indeed guard the young temporarily against per-
version. But when, later, either curiosity or the fashion of the
age brings such writings under their notice, will their youthful
conviction then stand the test? Whoever, in withstanding the
attacks of his opponent, has at his disposal only dogmatic
weapons, and is unable to develop the dialectic which lies
concealed in his own breast no less than in that of his an-
tagonist, [is in a dangerous position]. He sees sophistical
arguments, which have the attraction of novelty, set in oppo-
sition to sophistical arguments which no longer have that
attraction, but, on the contrary, tend to arouse the suspicion
that advantage has been taken of his youthful credulity. And
accordingly he comes to believe that there can be no better
way of showing that he has outgrown childish discipline than
by casting aside these well-meant warnings; and accustomed
as he is to dogmatism, he drinks deep draughts of the poison,
which destroys his principles by a counter-dogmatism. 
In academic teaching we ought to pursue the course
exactly opposite to that which is here recommended, pro-
P 604
vided always that the teaching is based on thorough instruc-
tion in the criticism of pure reason. For in order to bring the
principles of this criticism into operation as soon as possible,
and to show their sufficiency even when dialectical illusion is
at its height, it is absolutely necessary that the attacks which
seem so terrible to the dogmatist should be made to exercise
their full force upon the pupil's reason, which though still
weak has been enlightened through criticism, and that the pupil
should thus be allowed the opportunity of testing for himself,
one by one, by reference to the critical principles, how ground-
less are the assertions of those who have launched these attacks. 
As it is by no means difficult for him to resolve these arguments
into thin air, he early begins to feel his own capacity to secure
himself against such injurious deceptions, which must finally
lose for him all their illusory power. Those same blows which
destroy the structures of the enemy must indeed be equally
destructive to any speculative structure which he may per-
chance himself wish to erect. This does not, however, in the
least disturb him, since he has no need of any such shelter,
being still in possession of good expectations in the practical
sphere, where he may confidently hope to find firmer ground
upon which to erect his own rational and beneficial system. 
There is, therefore, properly speaking, no polemic in the
field of pure reason. Both parties beat the air, and wrestle with
their own shadows, since they go beyond the limits of nature,
where there is nothing that they can seize and hold with their
dogmatic grasp. Fight as they may, the shadows which they
cleave asunder grow together again forthwith, like the heroes
in Valhalla, to disport themselves anew in the bloodless con-
But neither can we admit that there is any sceptical em-
ployment of pure reason, such as might be entitled the prin-
ciple of neutrality in all its disputes. To set reason at variance
with itself, to supply it with weapons on both sides, and then
to look on, quietly and scoffingly, at the fierce struggle, is not,
from the dogmatic point of view, a seemly spectacle, but ap-
pears to suggest a mischievous and malevolent disposition. 
If, however, we consider the invincible obstinacy and the
boastfulness of those who argue dogmatically, and who refuse
to allow their claims to be moderated by any criticism, there
P 605
is really no other available course of action than to set against
the boasting of the one side the no less justified boasting of the
other, in the hope that the resistance thus offered to reason
may at least serve to disconcert it, to awaken some doubts as
to its pretensions, and to make it willing to give a hearing to
criticism. But to allow ourselves simply to acquiesce in these
doubts, and thereupon to set out to commend the conviction
and admission of our ignorance not merely as a remedy against
the complacency of the dogmatists, but likewise as the right
method of putting an end to the conflict of reason with itself,
is a futile procedure, and can never suffice to overcome the
restlessness of reason. At best it is merely a means of awaken-
ing it from its sweet dogmatic dreams, and of inducing it to
enter upon a more careful examination of its own position. 
Since, however, the sceptical method of escaping from the
troublesome affairs of reason appears to be, as it were, a short
cut by which we can arrive at a permanent peace in philosophy,
or [if it be not that], is at least the road favoured by those who
would feign make show of having a philosophical justification
for their contemptuous dislike of all enquiries of this kind, I
consider it necessary to exhibit this way of thinking in its true
The Impossibility of a Sceptical Satisfaction of Pure
Reason in its Internal Conflicts 
The consciousness of my ignorance (unless at the same
time this ignorance is recognised as being necessary), instead
of ending my enquiries, ought rather to be itself the reason
for entering upon them. All ignorance is either ignorance of
things or ignorance of the function and limits of knowledge. 
If ignorance is only accidental, it must incite me, in the former
regard to a dogmatic enquiry concerning things (objects), in
the latter regard to a critical enquiry concerning the limits of
my possible knowledge. But that my ignorance is absolutely
necessary, and that I am therefore absolved from all further
enquiry, cannot be established empirically, from observation,
but only through an examination, critically conducted, of the
primary sources of our knowledge. The determination of the
limits of our reason cannot, therefore, be made save on a priori
P 606
grounds; on the other hand, that limitation of it which con-
sists merely in an indeterminate knowledge of an ignorance
never to be completely removed, can be recognised a posteriori
by reference to that which, notwithstanding all we know, still
remains to be known. The former knowledge of our ignor-
ance, which is possible only through criticism of reason itself,
is science; the latter is nothing but perception, and we can-
not say how far the inferences from perception may extend. 
If I represent the earth as it appears to my senses, as a flat
surface, with a circular horizon, I cannot know how far it
extends. But experience teaches me that wherever I may go,
I always see a space around me in which I could proceed
further; and thus I know the limits of my actual knowledge
of the earth at any given time, but not the limits of all possible
geography. But if I have got so far as to know that the earth
is a sphere and that its surface is spherical, I am able even
from a small part of it, for instance, from the magnitude of a
degree, to know determinately, in accordance with principles
a priori, the diameter, and through it the total superficial area
of the earth; and although I am ignorant of the objects which
this surface may contain, I yet have knowledge in respect of
its circuit, magnitude, and limits. 
The sum of all the possible objects of our knowledge ap-
pears to us to be a plane, with an apparent horizon -- namely,
that which in its sweep comprehends it all, and which has been
entitled by us the idea of unconditioned totality. To reach
this concept empirically is impossible, and all attempts to
determine it a priori in accordance with an assured principle
have proved vain. None the less all the questions raised by our
pure reason are as to what may be outside the horizon, or, it
may be, on its boundary line. 
The celebrated David Hume was one of those geographers
of human reason who have imagined that they have sufficiently
disposed of all such questions by setting them outside the hori-
zon of human reason -- a horizon which yet he was not able
to determine. Hume dwelt in particular upon the principle of
causality, and quite rightly observed that its truth, and even
the objective validity of the concept of efficient cause in
P 607
general, is based on no insight, that is, on no a priori know-
ledge, and that its authority cannot therefore be ascribed to
its necessity, but merely to its general utility in the course of
experience, and to a certain subjective necessity which it
thereby acquires, and which he entitles custom. From the
incapacity of our reason to make use of this principle in any
manner that transcends experience, he inferred the nullity of
all pretensions of reason to advance beyond the empirical. 
A procedure of this kind -- subjecting the facts of reason
to examination, and if necessary to blame -- may be entitled
the censorship of reason. This censorship must certainly lead
to doubt regarding all transcendent employment of principles. 
But this is only the second step, and does not by any means
complete the work of enquiry. The first step in matters of pure
reason, marking its infancy, is dogmatic. The second step is
sceptical; and indicates that experience has rendered our judg-
ment wiser and more circumspect. But a third step, such as
can be taken only by fully matured judgment, based on as-
sured principles of proved universality, is now necessary,
namely, to subject to examination, not the facts of reason, but
reason itself, in the whole extent of its powers, and as regards
its aptitude for pure a priori modes of knowledge. This is not
the censorship but the criticism of reason, whereby not its
present bounds but its determinate [and necessary] limits,
not its ignorance on this or that point but its ignorance in
regard to all possible questions of a certain kind, are demon-
strated from principles, and not merely arrived at by way of
conjecture. Scepticism is thus a resting-place for human
reason, where it can reflect upon its dogmatic wanderings and
make survey of the region in which it finds itself, so that for
the future it may be able to choose its path with more certainty. 
But it is no dwelling-place for permanent settlement. Such can
be obtained only through perfect certainty in our knowledge,
alike of the objects themselves and of the limits within which
all our knowledge of objects is enclosed. 
Our reason is not like a plane indefinitely far extended,
the limits of which we know in a general way only; but must
rather be compared to a sphere, the radius of which can be
determined from the curvature of the arc of its surface -- that
P 608
is to say, from the nature of synthetic a priori propositions
 -- and whereby we can likewise specify with certainty its
volume and its limits. Outside this sphere (the field of experi-
ence) there is nothing that can be an object for reason; nay, the
very questions in regard to such supposed objects relate only
to subjective principles of a complete determination of those
relations which can come under the concepts of the under-
standing and which can be found within the empirical sphere. 
We are actually in possession of a priori synthetic modes
of knowledge, as is shown by the principles of understanding
which anticipate experience. If anyone is quite unable to
comprehend the possibility of these principles, he may at first
be inclined to doubt whether they actually dwell in us a -
priori; but he cannot on this account declare that they are
beyond the powers of the understanding, and so represent all
the steps which reason takes under their guidance as being null
and void. All that he can say is that if we could have insight into
their origin and authenticity, we should be able to determine
the scope and limits of our reason, but that until we can have
such insight any assertions as to the limits of reason are made
at random. And on this ground a general doubt regarding all
dogmatic philosophy, proceeding as such philosophy does with-
out criticism of reason itself, is entirely justified; but we cannot
therefore altogether deny to reason the right to take such for-
ward steps, once we have prepared and secured the way for
them by a more thorough preparation of the ground. For all
the concepts, nay, all the questions, which pure reason presents
to us, have their source not in experience, but exclusively in
reason itself, and must therefore allow of solution and of being
determined in regard to their validity or invalidity. We have no
right to ignore these problems, as if their solution really de-
pended on the nature of things, and as if we might therefore,
on the plea of our incapacity, decline to occupy ourselves with
their further investigation; for since reason is the sole begetter
of these ideas, it is under obligation to give an account of their
validity or of their illusory, dialectical nature. 
All sceptical polemic should properly be directed only
against the dogmatist, who, without any misgivings as to his
fundamental objective principles, that is, without criticism,
P 609
proceeds complacently upon his adopted path; it should be
designed simply to put him out of countenance and thus to
bring him to self-knowledge. In itself, however, this polemic
is of no avail whatsoever in enabling us to decide what it is
that we can and what it is that we cannot know. All unsuccess-
ful dogmatic attempts of reason are facts, and it is always of
advantage to submit them to the censorship of the sceptic. 
But this can decide nothing regarding those expectations of
reason which lead it to hope for better success in its future
attempts, and to build claims on this foundation; and con-
sequently no mere censorship can put an end to the dispute
regarding the rights of human reason. 
Hume is perhaps the most ingenious of all the sceptics, and
beyond all question is without rival in respect of the influence
which the sceptical procedure can exercise in awakening
reason to a thorough self-examination. It will therefore well
repay us to make clear to ourselves, so far as may be relevant to
our purpose, the course of the reasoning, and the errors, of so
acute and estimable a man -- a course of reasoning which at
the start was certainly on the track of truth. 
Hume was perhaps aware, although he never followed the
matter out, that in judgments of a certain kind we pass beyond
our concept of the object. I have entitled this kind of judg-
ments synthetic. There is no difficulty as to how, by means of
experience, I can pass beyond the concept which I previously
have. Experience is in itself a synthesis of perceptions,
whereby the concept which I have obtained by means of a
perception is increased through the addition of other per-
ceptions. But we suppose ourselves to be able to pass a priori
beyond our concept, and so to extend our knowledge. This we
attempt to do either through the pure understanding, in respect
of that which is at least capable of being an object of experi-
ence, or through pure reason, in respect of such properties of
things, or indeed even of the existence of such things, as can
never be met with in experience. Our sceptical philosopher did
not distinguish these two kinds of judgments, as he yet ought
to have done, but straightway proceeded to treat this self-
increment of concepts, and, as we may say, this spontaneous
generation on the part of our understanding and of our reason,
P 610
without impregnation by experience, as being impossible. 
He therefore regarded all the supposed a priori principles
of these faculties as fictitious, and concluded that they are
nothing but a custom-bred habit arising from experience
and its laws, and are consequently merely empirical, that is,
rules that are in themselves contingent, and to which we
ascribe a supposititious necessity and universality. In support
of his assertion of this startling thesis, he cited the universally
recognised principle of the relation between cause and effect. 
For since no faculty of understanding can carry us from the
concept of a thing to the existence of something else that is
thereby universally and necessarily given, he believed that he
was therefore in a position to conclude that in the absence of
experience we have nothing that can increase our concept and
justify us in propounding a judgment which thus enlarges
itself a priori. That sunlight should melt wax and yet also
harden clay, no understanding, he pointed out, can discover
from the concepts which we previously possessed of these
things, much less infer them according to a law. Only experi-
ence is able to teach us such a law. But, as we have discovered
in the Transcendental Logic, although we can never pass
immediately beyond the content of the concept which is given
us, we are nevertheless able, in relation to a third thing,
namely, possible experience, to know the law of its connection
with other things, and to do so in an a priori manner. If,
therefore, wax, which was formerly hard, melts, I can know
a priori that something must have preceded, ([that something
being] for instance [in this case] the heat of the sun), upon which
the melting has followed according to a fixed law, although
a priori, independently of experience, I could not determine,
in any specific manner, either the cause from the effect, or the
effect from the cause. Hume was therefore in error in inferring
from the contingency of our determination in accordance with
the law the contingency of the law itself. The passing be-
yond the concept of a thing to possible experience (which
takes place a priori and constitutes the objective reality of the
concept) he confounded with the synthesis of the objects of
actual experience, which is always empirical. He thus con-
founds a principle of affinity, which has its seat in the under-
standing and affirms necessary connection, with a rule of
P 611
association, which exists only in the imitative faculty of im-
agination, and which can exhibit only contingent, not objective
The sceptical errors of this otherwise singularly acute
thinker arose chiefly from a defect which he shares in common
with all dogmatists, namely, that he did not make a system-
atic review of all the various kinds of a priori synthesis as-
cribable to the understanding. For he would then have found,
to mention only one of many possible examples, that the prin-
ciple of permanence is a principle of this character, and that,
like the principle of causality, it anticipates experience. He
would thus have been able to prescribe determinate limits
to the activities whereby the understanding and pure reason
extend themselves a priori. Instead of so doing, he merely
restricts the understanding, without defining its limits, and
while creating a general mistrust fails to supply any deter-
minate knowledge of the ignorance which for us is un-
avoidable. For while subjecting to censorship certain prin-
ciples of the understanding, he makes no attempt to assess
the understanding itself, in respect of all its powers, by
the assay-balance of criticism; while rightly denying to the
understanding what it cannot really supply, he goes on to
deny it all power of extending itself a priori, and this in
spite of his never having tested it as a whole. Thus the fate
that waits upon all scepticism likewise befalls Hume, namely,
that his own sceptical teaching comes to be doubted, as being
based only on facts which are contingent, not on principles
which can constrain to a necessary renunciation of all right
to dogmatic assertions. 
Further, he draws no distinction between the well-
grounded claims of the understanding and the dialectical
pretensions of reason, though it is indeed chiefly against
the latter that his attacks are directed. Accordingly that
peculiarly characteristic ardour with which reason insists
upon giving free rein to itself, has not in the least been disturbed
but only temporarily impeded. It does not feel that it has been
shut out from the field in which it is wont to disport itself;
and so, in spite of its being thwarted in this and that direc-
tion, it cannot be made entirely to desist from these ventures. 
On the contrary, the attacks lead only to counter-preparations,
P 612
and make us the more obstinate in insisting upon our own views. 
But a complete review of all the powers of reason -- and the
conviction thereby obtained of the certainty of its claims to a
modest territory, as also of the vanity of higher pretensions --
puts an end to the conflict, and induces it to rest satisfied with
a limited but undisputed patrimony. 
To the uncritical dogmatist, who has not surveyed the
sphere of his understanding, and therefore has not determined,
in accordance with principles, the limits of his possible know-
ledge, these sceptical attacks are not only dangerous but even
destructive. For he does not know beforehand how far his
powers extend, and indeed believes that their limits can be
determined by the simple method of trial and failure. In con-
sequence of this, if on being attacked there is a single one of
his assertions that he is unable to justify, or which involves
illusion for which he also cannot account in terms of any
principles, suspicion falls on all his contentions, however
plausible they may appear. 
The sceptic is thus the taskmaster who constrains the dog-
matic reasoner to develop a sound critique of the understand-
ing and reason. When we have advanced thus far, we need
fear no further challenge, since we have learned to distinguish
our real possessions from that which lies entirely outside them;
and as we make no claims in regard to this latter domain,
we cannot become involved in any dispute in respect to it. 
While, therefore, the sceptical procedure cannot of itself yield
any satisfying answer to the questions of reason, none the
less it prepares the way by arousing reason to circumspection,
and by indicating the radical measures which are adequate
to secure it in its legitimate possessions. 
Section 3
Since criticism of our reason has at last taught us that
we cannot by means of its pure and speculative employment
arrive at any knowledge whatsoever, may it not seem that a
P 613
proportionately wider field is opened for hypotheses?  For are
we not at liberty, where we cannot make assertions, at least
to invent theories and to have opinions? 
If the imagination is not simply to be visionary, but is to
be inventive under the strict surveillance of reason, there must
always previously be something that is completely certain, and
not invented or merely a matter of opinion, namely, the
possibility of the object itself. Once that is established, it is
then permissible to have recourse to opinion in regard to its
actuality; but this opinion, if it is not to be groundless, must
be brought into connection with what is actually given and so
far certain, as serving to account for what is thus given. Then,
and only then, can the supposition be entitled an hypothesis. 
As we cannot form the least conception a priori of the
possibility of dynamical connection, and as the categories
of the pure understanding do not suffice for devising any such
conception, but only for apprehending it when met with in
experience, we cannot, in accordance with these categories,
creatively imagine any object in terms of any new quality
that does not allow of being given in experience; and we
cannot, therefore, make use of such an object in any legiti-
mate hypothesis; otherwise we should be resting reason on
empty figments of the brain, and not on concepts of things. 
Thus it is not permissible to invent any new original powers,
as, for instance, an understanding capable of intuiting its
objects without the aid of senses; or a force of attraction with-
out any contact; or a new kind of substance existing in space
and yet not impenetrable. Nor is it legitimate to postulate
a form of communion of substances which is different from
any revealed in experience, a presence that is not spatial,
a duration that is not temporal. In a word, our reason can
employ as conditions of the possibility of things only the
conditions of possible experience; it can never proceed to
form concepts of things quite independently of these con-
ditions. Such concepts, though not self-contradictory, would
be without an object. 
P 614
The concepts of reason are, as we have said, mere ideas,
and have no object that can be met with in any experience. 
None the less they do not on this account signify objects
that having been invented are thereupon assumed to be
possible. They are thought only problematically, in order
that upon them (as heuristic fictions), we may base regu-
lative principles of the systematic employment of the under-
standing in the field of experience. Save in this connection
they are merely thought-entities, the possibility of which is
not demonstrable, and which therefore do not allow of being
employed, in the character of hypotheses, in explanation of
the actual appearances. It is quite permissible to think the
soul as simple, in order, in conformity with this idea, to employ
as the principle of our interpretation of its inner appearances
a complete and necessary unity of all its faculties; and this in
spite of the fact that this unity is such as can never be appre-
hended in concreto. But to assume the soul as a simple sub-
stance (a transcendent concept), would be [to propound] a
proposition which is not only indemonstrable -- as is the case
with many physical hypotheses -- but is hazarded in a quite
blind and arbitrary fashion. For the simple can never be
met with in any experience whatsoever; and if by substance
be here meant the permanent object of sensible intuition, the
possibility of a simple appearance is quite incomprehensible. 
Reason does not afford any sufficient ground for assuming,
[even] as a matter of opinion, merely intelligible beings, or
merely intelligible properties of things belonging to the sen-
sible world, although (as we have no concepts of their pos-
sibility or impossibility) we also cannot lay claim to any insight
that justifies us in dogmatically denying them. 
In the explanation of given appearances, no things or
grounds of explanation can be adduced other than those
which have been found to stand in connection with given
appearances in accordance with the already known laws of the
appearances. A transcendental hypothesis, in which a mere
idea of reason is used in explanation of natural existences
would really be no explanation; so to proceed would be to
explain something, which in terms of known empirical prin-
ciples we do not understand sufficiently, by something which
P 615
we do not understand at all. Moreover, the principle of such
an hypothesis would at most serve only for the satisfaction of
reason, not for the furtherance of the employment of the
understanding in respect of objects. Order and purposiveness
in nature must themselves be explained from natural grounds
and according to natural laws; and the wildest hypotheses, if
only they are physical, are here more tolerable than a hyper-
physical hypothesis, such as the appeal to a divine Author,
assumed simply in order that we may have an explanation. 
That would be a principle of ignava ratio; for we should be
passing over all causes the objective reality of which, at least
as regards their possibility, can be ascertained in the course
of experience, in order to rest in a mere idea -- an idea that is
very comforting to reason. As regards the absolute totality of
the ground of explanation of the series of these causes, such
totality need suggest no difficulty in respect of natural exist-
ences; since these existences are nothing but appearances, we
need never look to them for any kind of completeness in the
synthesis of the series of conditions. 
It can never be permissible, in the speculative employment
of reason, to resort to transcendental hypotheses, and to pre-
sume that we can make good the lack of physical grounds of
explanation by appealing to the hyperphysical. The objection
to such procedure is twofold: partly, that reason, so far from
being in the least advanced thereby, is cut off from all progress
in its own employment; partly, that this license would in the
end deprive reason of all the fruits that spring from the cul-
tivation of its own proper domain, namely, that of experience. 
For whenever the explanation of natural existences is found
to be difficult, there is always at hand a transcendental ground
of explanation which relieves us from further investigation,
and our enquiry is brought to an end not through insight, but
by the aid of a principle which while utterly incomprehensible
has from the start been so constructed as necessarily to con-
tain the concept of what is absolutely primordial. 
The second requirement for the admissibility of an hypo-
thesis is its adequacy in accounting a priori for those con-
sequences which are [de facto] given. If for this purpose we
have to call in auxiliary hypotheses, they give rise to the sus-
P 616
picion that they are mere fictions; for each of them requires the
same justification as is necessary in the case of the fundamental
hypothesis, and they are not, therefore, in a position to bear
reliable testimony. If we assume an absolutely perfect cause,
we need not be at a loss in explaining the purposiveness, order,
and vastness which are displayed in the world; but in view of
what, judged at least by our concepts, are the obvious devia-
tions and evils, other new hypotheses are required in order to
uphold the original hypothesis in face of the objections which
these suggest. If the simple self-sufficiency of the human soul
has been employed to account for its appearances, it is contro-
verted by certain difficulties, due to those phenomena which
are similar to the changes that take place in matter (growth
and decay), and we have therefore to seek the aid of new
hypotheses, which are not indeed without plausibility, but
which yet have no credentials save what is conferred upon
them by that opinion -- the fundamental hypothesis -- which
they have themselves been called in to support. 
If the instances here cited as examples of the assertions
made by reason -- the incorporeal unity of the soul and the
existence of a supreme being -- are propounded not as hypo-
theses, but as dogmas proved a priori, I am not at present
concerned with them, save to remark that in that case care
must be taken that the proof has the apodeictic certainty of a
demonstration. For to set out to show no more than that the
reality of such ideas is probable is as absurd as to think of
proving a proposition of geometry merely as a probability. 
Reason, when employed apart from all experience, can know
propositions entirely a priori, and as necessary, or it can know
nothing at all. Its judgments, therefore, are never opinions;
either it must abstain from all judgment, or must affirm with
apodeictic certainty. Opinions and probable judgments as to
what belongs to things can be propounded only in explana-
tion of what is actually given, or as consequences that follow
in accordance with empirical laws from what underlies the
actually given. They are therefore concerned only with the
series of the objects of experience. Outside this field, to form
opinions is merely to play with thoughts. For we should then
have to presuppose yet another opinion -- the opinion that we
may perhaps arrive at the truth by a road that is uncertain. 
P 617
But although, in dealing with the merely speculative ques-
tions of pure reason, hypotheses are not available for the
purposes of basing propositions upon them, they are yet entirely
permissible for the purposes of defending propositions; that is
to say, they may not be employed in any dogmatic, but only in
polemical fashion. By the defence of propositions I do not
mean the addition of fresh grounds for their assertion, but
merely the nullifying of the sophistical arguments by which
our opponent professes to invalidate this assertion. Now all
synthetic propositions of pure reason have this peculiarity, that
while in asserting the reality of this or that idea we can never
have knowledge sufficient to give certainty to our proposition,
our opponent is just as little able to assert the opposite. This
equality of fortune [in the ventures] of human reason does not,
in speculative modes of knowledge, favour either of the two
parties, and it is consequently the fitting battle-ground for
their never-ending feuds. But as will be shown, reason has, in
respect of its practical employment, the right to postulate what
in the field of mere speculation it can have no kind of right
to assume without sufficient proof. For while all such assump-
tions do violence to [the principle of] completeness of specu-
lation, that is a principle with which the practical interest is
not at all concerned. In the practical sphere reason has rights
of possession, of which it does not require to offer proof, and of
which, in fact, it could not supply proof. The burden of proof
accordingly rests upon the opponent. But since the latter knows
just as little of the object under question, in trying to prove its
non-existence, as does the former in maintaining its reality,
it is evident that the former, who is asserting something as a
practically necessary supposition, is at an advantage (melior
est conditio possidentis). For he is at liberty to employ, as it
were in self-defence, on behalf of his own good cause, the very
same weapons that his opponent employs against that cause,
that is, hypotheses. These are not intended to strengthen the
proof of his position, but only to show that the opposing party
has much too little understanding of the matter in dispute
to allow of his flattering himself that he has the advantage
in respect of speculative insight. 
Hypotheses are therefore, in the domain of pure reason,
permissible only as weapons of war, and only for the purpose
P 618
of defending a right, not in order to establish it. But the oppos-
ing party we must always look for in ourselves. For specula-
tive reason in its transcendental employment is in itself
dialectical; the objections which we have to fear lie in our-
selves. We must seek them out, just as we would do in the
case of claims that, while old, have never become superannu-
ated, in order that by annulling them we may establish a
permanent peace. External quiescence is merely specious. 
The root of these disturbances, which lies deep in the nature
of human reason, must be removed. But how can we do so,
unless we give it freedom, nay, nourishment, to send out
shoots so that it may discover itself to our eyes, and that it
may then be entirely destroyed? We must, therefore, bethink
ourselves of objections which have never yet occurred to any
opponent, and indeed lend him our weapons, and grant him
the most favourable position which he could possibly desire. 
We have nothing to fear in all this, but much to hope for;
namely, that we may gain for ourselves a possession which
can never again be contested. 
Thus for our complete equipment we require among other
things the hypotheses of pure reason. For although they are
but leaden weapons, since they are not steeled by any law of ex-
perience, they are yet as effective as those which our opponents
can employ against us. If, therefore, having assumed (in some
non-speculative connection) the nature of the soul to be im-
material and not subject to any corporeal change, we are met
by the difficulty that nevertheless experience seems to prove
that the exaltation and the derangement of our mental powers
are alike in being merely diverse modifications of our organs,
we can weaken the force of this proof by postulating that our
body may be nothing more than a fundamental appearance
which in this our present state (in this life) serves as a condition
of our whole faculty of sensibility, and therewith of all our
thought, and that separation from the body may therefore
be regarded as the end of this sensible employment of our
faculty of knowledge and the beginning of its intellectual
employment. Thus regarded, the body would not be the cause
of thought, but merely a restrictive condition of it, and there-
fore, while indeed furthering the sensible and animal life, it
would because of this very fact have to be considered a hind-
P 619
rance to the pure and spiritual life. The dependence of the
animal and sensible upon the bodily constitution would then
in nowise prove the dependence of our entire life upon the
state of our organs. We might go yet further, and discover
quite new objections, which either have never been suggested
or have never been sufficiently developed. 
Generation, in man as in non-rational creatures, is de-
pendent upon opportunity, often indeed upon sufficiency of
food, upon the moods and caprices of rulers, nay, even upon
vice. And this makes it very difficult to suppose that a creature
whose life has its first beginning in circumstances so trivial
and so entirely dependent upon our own choice, should have
an existence that extends to all eternity. As regards the con-
tinuance (here on earth) of the species as a whole, this diffi-
culty is negligible, since accident in the individual case is still
subject to a general law, but as regards each individual it
certainly seems highly questionable to expect so potent an
effect from causes so insignificant. But to meet these objec-
tions we can propound a transcendental hypothesis, namely,
that all life is, strictly speaking, intelligible only, is not sub-
ject to changes of time, and neither begins in birth nor ends
in death; that this life is an appearance only, that is, a sen-
sible representation of the purely spiritual life, and that the
whole sensible world is a mere picture which in our present
mode of knowledge hovers before us, and like a dream has
in itself no objective reality; that if we could intuit our-
selves and things as they are, we should see ourselves in
a world of spiritual beings, our sole and true community
with which has not begun through birth and will not cease
through bodily death -- both birth and death being mere
Now of all this we have not the least knowledge. We plead
it only in hypothetical fashion, to meet the attack; we are not
actually asserting it. For it is not even an idea of reason, but
is a concept devised merely for the purposes of self-defence. 
None the less we are here proceeding in entire conformity
with reason. Our opponent falsely represents the absence of
empirical conditions as itself amounting to proof of the total
P 620
impossibility of our belief, and is therefore proceeding on
the assumption that he has exhausted all the possibilities. 
What we are doing is merely to show that it is just as little
possible for him to comprehend the whole field of possible
things through mere laws of experience as it is for us to reach,
outside experience, any conclusions justifiable for our reason. 
Anyone who employs such hypothetical means of defence
against the rash and presumptuous negations of his opponent
must not be considered to intend the adoption of these opinions
as his own; he abandons them, as soon as he has disposed
of the dogmatic pretensions of his opponent. For though
a merely negative attitude to the assertions of others may
seem very modest and moderate, to proceed to represent
the objections to an assertion as proofs of the counter-asser-
tion is to make claims no less presumptuous and visionary
than if the positive position and its affirmations had been
It is evident, therefore, that in the speculative employment
of reason hypotheses, regarded as opinions, have no validity
in themselves, but only relatively to the transcendent pre-
tensions of the opposite party. For to make principles of pos-
sible experience conditions of the possibility of things in general
is just as transcendent a procedure as to assert the objective
reality of [transcendent] concepts, the objects of which can-
not be found anywhere save outside the limits of all possible
experience. What pure reason judges assertorically, must
(like everything that reason knows) be necessary; otherwise
nothing at all is asserted. Accordingly, pure reason does
not, in point of fact, contain any opinions whatsoever. The
hypotheses, above referred to, are merely problematic judg-
ments, which at least cannot be refuted, although they do
not indeed allow of any proof. They are therefore nothing
but private opinions. Nevertheless, we cannot properly dis-
pense with them as weapons against the misgivings which
are apt to occur; they are necessary even to secure our inner
tranquillity. We must preserve to them this character, care-
fully guarding against the assumption of their independent
authority or absolute validity, since otherwise they would
drown reason in fictions and delusions. 
P 621
Section 4
What distinguishes the proofs of transcendental synthetic
propositions from all other proofs which yield an a priori
synthetic knowledge is that, in the case of the former, reason
may not apply itself, by means of its concepts, directly to the
object, but must first establish the objective validity of the
concepts and the possibility of their a priori synthesis. This
rule is not made necessary merely by considerations of prud-
ence, but is essential to the very possibility of the proofs them-
selves. If I am to pass a priori beyond the concept of an object,
I can do so only with the help of some special guidance,
supplied from outside this concept. In mathematics it is a -
priori intuition which guides my synthesis; and thereby all
our conclusions can be drawn immediately from pure intuition. 
In transcendental knowledge, so long as we are concerned
only with concepts of the understanding, our guide is the
possibility of experience. Such proof does not show that the
given concept (for instance, of that which happens) leads
directly to another concept (that of a cause); for such a transi-
tion would be a saltus which could not be justified. The proof
proceeds by showing that experience itself, and therefore the
object of experience, would be impossible without a connec-
tion of this kind. Accordingly, the proof must also at the
same time show the possibility of arriving synthetically
and a priori at some knowledge of things which was not
contained in the concepts of them. Unless this requirement
be met, the proofs, like streams which break their banks,
run wildly at random, whithersoever the current of hidden
association may chance to lead them. The semblance of con-
viction which rests upon subjective causes of association,
and which is regarded as insight into a natural affinity, can-
not balance the misgivings to which so hazardous a course
must rightly give rise. On this account, all attempts to prove
the principle of sufficient reason have, by the universal ad-
P 622
mission of those concerned, been fruitless; and prior to our
own transcendental criticism it was considered better, since
that principle could not be surrendered, boldly to appeal to
the common sense of mankind -- an expedient which always
is a sign that the cause of reason is in desperate straits --
rather than to attempt new dogmatic proofs. 
But if the proposition to be proved is an assertion of pure
reason, and if I am therefore proposing to pass beyond my em-
pirical concepts by means of mere ideas, justification of such a
step in synthesis (supposing it to be possible) is all the more
necessary as a precondition of any attempt to prove the proposi-
tion itself. However plausible the alleged proof of the simple
nature of our thinking substance, derived from the unity of
apperception, may be, it is faced by the unavoidable difficulty,
that since the [notion of] absolute simplicity is not a concept
which can be immediately related to a perception, but, as an
idea, would have to be inferred, there can be no understanding
how the bare consciousness (which is, or at least can be,
contained in all thought), though it is indeed so far a simple
representation, should conduct us to the consciousness and the
knowledge of a thing in which thought alone can be contained. 
If I represent to myself the power of a body in motion, it is
so far for me absolute unity, and my representation of it is
simple; and I can therefore express this representation by the
motion of a point -- for the volume of the body is not here a
relevant consideration, and can be thought, without diminution
of the moving power, as small as we please, and therefore even
as existing in a point. But I may not therefore conclude that
if nothing be given to me but the moving power of a body, the
body can be thought as simple substance -- merely because its
representation abstracts from the magnitude of its volume
and is consequently simple. The simple arrived at by abstrac-
tion is entirely different from the simple as an object; though
the 'I', taken in abstraction, can contain in itself no manifold,
in its other meaning, as signifying the soul itself, it can be a
highly complex concept, as containing under itself, and as
denoting, what is very composite. I thus detect in these
arguments a paralogism. But in order to be armed against this
P 623
paralogism (for without some forewarning we should not
entertain any suspicion in regard to the proof), it is indis-
pensably necessary to have constantly at hand a criterion of
the possibility of those synthetic propositions which are in-
tended to prove more than experience yields. This criterion
consists in the requirement that proof should not proceed
directly to the desired predicate but only by means of a prin-
ciple that will demonstrate the possibility of extending our
given concept in an a priori manner to ideas, and of
realising the latter. If this precaution be always observed, if
before attempting any proof, we discreetly take thought as to
how, and with what ground for hope, we may expect such an
extension through pure reason, and whence, in such a case,
this insight, which is not developed from concepts, and
also cannot be anticipated in reference to any possible ex-
perience, is yet to be derived, we can by so doing spare our-
selves much difficult and yet fruitless labour, not expecting
from reason what obviously exceeds its power -- or rather, since
reason, when obsessed by passionate desire for the speculative
enlargement of its domain, is not easily to be restrained, by
subjecting it to the discipline of self-control. 
The first rule is, therefore, not to attempt any tran-
scendental proofs until we have considered, with a view to
obtaining justification for them, from what source we propose
to derive the principles on which the proofs are to be based,
and with what right we may expect success in our inferences. 
If they are principles of the understanding (for instance, that of
causality), it is useless to attempt, by means of them, to attain
to ideas of pure reason; such principles are valid only for
objects of possible experience. If they are principles of pure
reason, it is again labour lost. Reason has indeed principles
of its own; but regarded as objective principles, they are one
and all dialectical, and can have no validity save as regulative
principles for its employment in experience, with a view to
making experience systematically coherent. But if such pro-
fessed proofs are propounded, we must meet their deceptive
power of persuasion with the non liquet of our matured
judgment; and although we may not be able to detect the
illusion involved, we are yet entirely within our rights in
demanding a deduction of the principles employed in them;
P 624
and if these principles have their source in reason alone,
the demand is one which can never be met. And there is
thus no need for us to concern ourselves with the particular
nature and with the refutation of each and every ground-
less illusion; at the tribunal of a critical reason, which insists
upon laws, this entire dialectic, so inexhaustible in its artifices,
can be disposed of in bulk. 
The second peculiarity of transcendental proofs is that
only one proof can be found for each transcendental proposi-
tion. If I am inferring not from concepts but from the intuition
which corresponds to a concept, be it a pure intuition as in
mathematics, or an empirical intuition as in natural science,
the intuition which serves as the basis of the inference supplies
me with manifold material for synthetic propositions, material
which I can connect in more than one way, so that, as it is
permissible for me to start from more than one point, I can
arrive at the same proposition by different paths. 
In the case of transcendental propositions, however, we
start always from one concept only, and assert the synthetic
condition of the possibility of the object in accordance with
this concept. Since outside this concept there is nothing
further through which the object could be determined, there
can therefore be only one ground of proof. The proof can
contain nothing more than the determination of an object in
general in accordance with this one single concept. In the
Transcendental Analytic, for instance, we derived the prin-
ciple that everything which happens has a cause, from the
condition under which alone a concept of happening in general
is objectively possible -- namely, by showing that the determina-
tion of an event in time, and therefore the event as belonging
to experience, would be impossible save as standing under such
a dynamical rule. This is the sole possible ground of proof; for
the event, in being represented, has objective validity, that is,
truth, only in so far as an object is determined for the concept
by means of the law of causality. Other proofs of this principle
have, indeed, been attempted, for instance, from the con-
tingency [of that which happens]. But on examining this
argument, we can discover no mark of contingency save only
the happening, that is, the existence of the object preceded
by its non-existence, and thus are brought back to the same
P 625
ground of proof as before. Similarly, if the proposition, that
everything which thinks is simple, is to be proved, we leave
out of account the manifold of thought, and hold only to the
concept of the 'I', which is simple and to which all thought
is related. The same is true of the transcendental proof of the
existence of God; it is based solely on the coincidence of the
concepts of the most real being and of necessary being, and
is not to be looked for anywhere else. 
This caution reduces the criticism of the assertions of
reason to very small compass. When reason is conducting
its business through concepts only, there is but one possible
proof, if, that is to say, there be any possible proof at all. If,
therefore, we observe the dogmatist coming forward with ten
proofs, we can be quite sure that he really has none. For had
he one that yielded -- as must always be required in matters of
pure reason -- apodeictic proof, what need would he have of
the others? His purpose can only be that of the parliamentary
advocate, who intends his various arguments for different
groups, in order to take advantage of the weakness of those
before whom he is pleading -- hearers who, without entering
deeply into the matter, desire to be soon quit of it, and there-
fore seize upon whatever may first happen to attract their at-
tention, and decide accordingly. 
The third rule peculiar to pure reason, in so far as it is to
be subjected to a discipline in respect of transcendental proofs,
is that its proofs must never be apagogical, but always osten-
sive. The direct or ostensive proof, in every kind of knowledge,
is that which combines with the conviction of its truth insight
into the sources of its truth; the apagogical proof, on the other
hand, while it can indeed yield certainty, cannot enable us
to comprehend truth in its connection with the grounds of its
possibility. The latter is therefore to be regarded rather as a
last resort than as a mode of procedure which satisfies all the
requirements of reason. In respect of convincing power, it has,
however, this advantage over the direct proofs, that contradic-
tion always carries with it more clearness of representation than
the best connection, and so approximates to the intuitional
certainty of a demonstration. 
The real reason why apagogical proofs are employed in
P 626
various sciences would seem to be this. When the grounds
from which this or that knowledge has to be derived are too
numerous or too deeply concealed, we try whether we may not
arrive at the knowledge in question through its consequences. 
Now this modus ponens, that is, the inference to the truth of an
assertion from the truth of its consequences, is only permissible
when all its possible consequences are [known to be] true; for
in that case there is only one possible ground for this being
so, and that ground must also be true. But this procedure
is impracticable; to discover all possible consequences of
any given proposition exceeds our powers. None the less this
mode of reasoning is resorted to, although indeed with a cer-
tain special modification, when we endeavour to prove some-
thing merely as an hypothesis. The modification made is that
we admit the conclusion as holding according to analogy,
namely, on the ground that if all the many consequences
examined by us agree with an assumed ground, all other
possible consequences will also agree with it. But from the
nature of the argument, it is obvious that an hypothesis can
never, on such evidence, be transformed into demonstrated
truth. The modus tollens of reasoning, which proceeds from
consequences to their grounds, is not only a quite rigorous but
also an extremely easy mode of proof. For if even a single false
consequence can be drawn from a proposition, the proposition
is itself false. Instead, then, as in an ostensive proof, of re-
viewing the whole series of grounds that can lead us to the
truth of a proposition, by means of a complete insight into its
possibility, we require only to show that a single one of the
consequences resulting from its opposite is false, in order to
prove that this opposite is itself false, and that the proposition
which we had to prove is therefore true. 
The apagogic method of proof is, however, permissible
only in those sciences where it is impossible mistakenly to
substitute what is subjective in our representations for what is
objective, that is, for the knowledge of that which is in the
object. Where such substitution tends to occur, it must often
happen that the opposite of a given proposition contradicts
only the subjective conditions of thought, and not the object,
or that the two propositions contradict each other only under
a subjective condition which is falsely treated as being object-
P 627
ive; the condition being false, both can be false, without it
being possible to infer from the falsity of the one to the truth of
the other. 
In mathematics this subreption is impossible; and it is
there, therefore, that apagogical proofs have their true place. 
In natural science, where all our knowledge is based upon
empirical intuitions, the subreption can generally be guarded
against through repeated comparison of observations; but in
this field this mode of proof is for the most part of little im-
portance. The transcendental enterprises of pure reason,
however, are one and all carried on within the domain proper
to dialectical illusion, that is, within the domain of the sub-
jective, which in its premisses presents itself to reason, nay,
forces itself upon reason, as being objective. In this field, there-
fore, it can never be permissible, so far as synthetic propositions
are concerned, to justify assertions by disproving their opposite. 
For either this refutation is nothing but the mere representa-
tion of the conflict of the opposite opinion with the subjective
conditions under which alone anything can be conceived by
our reason, which does not in the least contribute to the dis-
proof of the thing itself-- just as, for instance, we must recog-
nise that while the unconditioned necessity of the existence of
a being is altogether inconceivable to us, and that every
speculative proof of a necessary supreme being is therefore
rightly to be opposed on subjective grounds, we have yet no
right to deny the possibility of such a primordial being in
itself -- or else both parties, those who adopt the affirmative
no less than those who adopt the negative position, have
been deceived by transcendental illusion, and base their asser-
tions upon an impossible concept of the object. In that case
we can apply the rule: non entis nulla sunt predicata; that
is, all that is asserted of the object, whether affirmatively or
negatively, is erroneous, and consequently we cannot arrive
apagogically at knowledge of the truth through refutation of
the opposite. If, for instance, it be assumed that the sensible
world is given in itself in its totality, it is false that it must be
either infinite in space or finite and limited. Both contentions
are false. For appearances (as mere representations) which yet
are to be given in themselves (as objects) are something impos-
sible; and though the infinitude of this imaginary whole would
P 628
indeed be unconditioned, it would contradict (since everything
in appearances is conditioned) the unconditioned determina-
tion of magnitude, [that is, of totality], which is presupposed
in the concept. 
The apagogic method of proof is the real deluding influ-
ence by which those who reason dogmatically have always held
their admirers. It may be compared to a champion who seeks
to uphold the honour and incontestable rights of his adopted
party by offering battle to all who would question them. Such
boasting proves nothing, however, in regard to the merits of the
issue but only in regard to the respective strength of the com-
batants, and this indeed only in respect of those who take the
offensive. The spectators, observing that each party is alter-
nately conqueror and conquered, are often led to have scep-
tical doubts in regard to the very object of the dispute. They
are not, however, justified in adopting such an attitude; it is
sufficient to declare to the combatants: non defensoribus istis
tempus eget. Everyone must defend his position directly, by a
legitimate proof that carries with it a transcendental deduction
of the grounds upon which it is itself made to rest. Only when
this has been done, are we in a position to decide how far its
claims allow of rational justification. If an opponent relies on
subjective grounds, it is an easy matter to refute him. The
dogmatist cannot, however, profit by this advantage. His own
judgments are, as a rule, no less dependent upon subjective
influences; and he can himself in turn be similarly cornered by
his opponent. But if both parties proceed by the direct method,
either they will soon discover the difficulty, nay, the impossi-
bility, of showing ground for their assertions, and will be left
with no resort save to appeal to some form of prescriptive
authority; or our criticism will easily discover the illusion to
which their dogmatic procedure is due, compelling pure
reason to relinquish its exaggerated pretensions in the realm
of speculation, and to withdraw within the limits of its proper
territory -- that of practical principles. 
P 629
IT is humiliating to human reason that it achieves nothing in
its pure employment, and indeed stands in need of a discipline
to check its extravagances, and to guard it against the decep-
tions which arise therefrom. But, on the other hand, reason
is reassured and gains self-confidence, on finding that it itself
can and must apply this discipline, and that it is not called
upon to submit to any outside censorship; and, moreover, that
the limits which it is compelled to set to its speculative employ-
ment likewise limit the pseudo-rational pretensions of all its
opponents, and that it can secure against all attacks whatever
may remain over from its former exaggerated claims. The
greatest and perhaps the sole use of all philosophy of pure
reason is therefore only negative; since it serves not as an
organon for the extension but as a discipline for the limitation
of pure reason, and, instead of discovering truth, has only the
modest merit of guarding against error. 
There must, however, be some source of positive modes of
knowledge which belong to the domain of pure reason, and
which, it may be, give occasion to error solely owing to mis-
understanding, while yet in actual fact they form the goal to-
wards which reason is directing its efforts. How else can we
account for our inextinguishable desire to find firm footing
somewhere beyond the limits of experience? Reason has a pre-
sentiment of objects which possess a great interest for it. But
when it follows the path of pure speculation, in order to ap-
proach them, they fly before it. Presumably it may look for
better fortune in the only other path which still remains open
to it, that of its practical employment. 
P 630
I understand by a canon the sum-total of the a priori prin-
ciples of the correct employment of certain faculties of know-
ledge. Thus general logic, in its analytic portion, is a canon
for understanding and reason in general; but only in regard
to their form; it abstracts from all content. The transcendental
analytic has similarly been shown to be the canon of the pure
understanding; for understanding alone is capable of true syn-
thetic modes of knowledge a priori. But when no correct em-
ployment of a faculty of knowledge is possible there is no
canon. Now all synthetic knowledge through pure reason in
its speculative employment is, as has been shown by the proofs
given, completely impossible. There is therefore no canon of
its speculative employment; such employment is entirely dia-
lectical. All transcendental logic is, in this respect, simply a
discipline. Consequently, if there be any correct employment
of pure reason, in which case there must be a canon of its
employment, the canon will deal not with the speculative but
with the practical employment of reason. This practical em-
ployment of reason we shall now proceed to investigate. 
Section 1
Reason is impelled by a tendency of its nature to go out
beyond the field of its empirical employment, and to venture
in a pure employment, by means of ideas alone, to the utmost
limits of all knowledge, and not to be satisfied save through
the completion of its course in [the apprehension of] a self-
subsistent systematic whole. Is this endeavour the outcome
merely of the speculative interests of reason? Must we not
rather regard it as having its source exclusively in the prac-
tical interests of reason? 
I shall, for the moment, leave aside all question as to the
success which attends pure reason in its speculative exercise,
and enquire only as to the problems the solution of which
P 631
constitutes its ultimate aim, whether reached or not, and in
respect of which all other aims are to be regarded only as
means. These highest aims must, from the nature of reason,
have a certain unity, in order that they may, as thus unified,
further that interest of humanity which is subordinate to no
higher interest. 
The ultimate aim to which the speculation of reason in its
transcendental employment is directed concerns three objects:
the freedom of the will, the immortality of the soul, and the
existence of God. In respect of all three the merely speculative
interest of reason is very small; and for its sake alone we should
hardly have undertaken the labour of transcendental investiga-
tion -- a labour so fatiguing in its endless wrestling with in-
superable difficulties -- since whatever discoveries might be
made in regard to these matters, we should not be able to make
use of them in any helpful manner in concreto, that is, in the
study or nature. If the will be free, this can have a bearing only
on the intelligible cause of our volition. For as regards the phe-
nomena of its outward expressions, that is, of our actions, we
must account for them -- in accordance with a maxim which
is inviolable, and which is so fundamental that without it we
should not be able to employ reason in any empirical manner
whatsoever -- in the same manner as all other appearances of
nature, namely, in conformity with unchangeable laws. If,
again, we should be able to obtain insight into the spiritual
nature of the soul, and therewith of its immortality, we could
make no use of such insight in explaining either the appear-
ances of this present life or the specific nature of a future
state. For our concept of an incorporeal nature is merely nega-
tive, and does not in the least extend our knowledge, yielding
no sufficient material for inferences, save only such as are
merely fictitious and cannot be sanctioned by philosophy. If,
thirdly, the existence of a supreme intelligence be proved, by
its means we might indeed render what is purposive in the
constitution and ordering of the world comprehensible in a
general sort or way, but we should not be in the least war-
ranted in deriving from it any particular arrangement or dis-
position, or in boldly inferring any such, where it is not per-
ceived. For it is a necessary rule of the speculative employment
of reason, not to pass over natural causes, and, abandoning
P 632
that in regard to which we can be instructed by experience, to
deduce something which we know from something which en-
tirely transcends all our [possible] knowledge. In short, these
three propositions are for speculative reason always tran-
scendent, and allow of no immanent employment -- that is,
employment in reference to objects of experience, and so in
some manner really of service to us -- but are in themselves,
notwithstanding the very heavy labours which they impose
upon our reason, entirely useless. 
If, then, these three cardinal propositions are not in any
way necessary for knowledge, and are yet strongly recom-
mended by our reason, their importance, properly regarded,
must concern only the practical. 
By 'the practical' I mean everything that is possible
through freedom. When, however, the conditions of the exer-
cise of our free will are empirical, reason can have no other
than a regulative employment in regard to it, and can serve
only to effect unity in its empirical laws. Thus, for instance,
in the precepts of prudence, the whole business of reason
consists in uniting all the ends which are prescribed to us by
our desires in the one single end, happiness, and in co-
ordinating the means for attaining it. In this field, therefore,
reason can supply none but pragmatic laws of free action, for
the attainment of those ends which are commended to us by
the senses; it cannot yield us laws that are pure and deter-
mined completely a priori. Laws of this latter type, pure prac-
tical laws, whose end is given through reason completely a -
priori, and which are prescribed to us not in an empirically
conditioned but in an absolute manner, would be products of
pure reason. Such are the moral laws; and these alone, there-
fore, belong to the practical employment of reason, and allow
of a canon. 
The whole equipment of reason, in the discipline which
may be entitled pure philosophy, is in fact determined with
a view to the three above-mentioned problems. These, how-
ever, themselves in turn refer us yet further, namely, to the
problem what we ought to do, if the will is free, if there is
a God and a future world. As this concerns our attitude to
the supreme end, it is evident that the ultimate intention
of nature in her wise provision for us has indeed, in the
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constitution of our reason, been directed to moral interests
But we must be careful, in turning our attention to an
object which is foreign to transcendental philosophy, that we
do not indulge in digressions to the detriment of the unity of
the system, nor on the other hand, by saying too little on this
new topic, fail in producing conviction through lack of clear-
ness. I hope to avoid both dangers, by keeping as close as
possible to the transcendental, and by leaving entirely aside
any psychological, that is, empirical, factors that may per-
chance accompany it. 
I must first remark that for the present I shall employ the
concept of freedom in this practical sense only, leaving aside
that other transcendental meaning which cannot be empiric-
ally made use of in explanation of appearances, but is itself
a problem for reason, as has been already shown. A will is
purely animal (arbitrium brutum), which cannot be deter-
mined save through sensuous impulses, that is, pathologically. 
A will which can be determined independently of sensuous
impulses, and therefore through motives which are repre-
sented only by reason, is entitled free will (arbitrium liberum),
and everything which is bound up with this will, whether as
ground or as consequence, is entitled practical. [The fact of]
practical freedom can be proved through experience. For the
human will is not determined by that alone which stimulates,
that is, immediately affects the senses; we have the power to
overcome the impressions on our faculty of sensuous desire, by
calling up representations of what, in a more indirect manner,
is useful or injurious. But these considerations, as to what is
desirable in respect of our whole state, that is, as to what is
good and useful, are based on reason. 
++ All practical concepts relate to objects of satisfaction or dis-
satisfaction, that is, of pleasure and pain, and therefore, at least
indirectly, to the objects of our feelings. But as feeling is not a faculty
whereby we represent things, but lies outside our whole faculty of
knowledge, the elements of our judgments so far as they relate to
pleasure or pain, that is, the elements of practical judgments, do not
belong to transcendental philosophy, which is exclusively concerned
with pure a priori modes of knowledge. 
P 633
Reason therefore provides
P 634
laws which are imperatives, that is, objective laws of freedom,
which tell us what ought to happen -- although perhaps it never
does happen -- therein differing from laws of nature, which
relate only to that which happens. These laws are therefore to
be entitled practical laws. 
 Whether reason is not, in the actions through which it
prescribes laws, itself again determined by other influences,
and whether that which, in relation to sensuous impulses, is
entitled freedom, may not, in relation to higher and more
remote operating causes, be nature again, is a question which
in the practical field does not concern us, since we are de-
manding of reason nothing but the rule of conduct; it is a
merely speculative question, which we can leave aside so long
as we are considering what ought or ought not to be done. 
While we thus through experience know practical freedom to
be one of the causes in nature, namely, to be a causality of
reason in the determination of the will, transcendental free-
dom demands the independence of this reason -- in respect of
its causality, in beginning a series of appearances -- from all
determining causes of the sensible world. Transcendental
freedom is thus, as it would seem, contrary to the law of
nature, and therefore to all possible experience; and so re-
mains a problem. But this problem does not come within the
province of reason in its practical employment; and we have
therefore in a canon of pure reason to deal with only two
questions, which relate to the practical interest of pure reason,
and in regard to which a canon of its employment must be
possible -- Is there a God? and, Is there a future life? The
question of transcendental freedom is a matter for speculative
knowledge only, and when we are dealing with the practical
we can leave it aside as being an issue with which we have
no concern. Moreover, a quite sufficient discussion of it is to
be found in the antinomy of pure reason. 
P 635
Section 2
Reason, in its speculative employment, conducted us
through the field of experience, and since it could not find
complete satisfaction there, from thence to speculative
ideas, which, however, in the end brought us back to experi-
ence. In so doing the ideas fulfilled their purpose, but in a
manner which, though useful, is not in accordance with our
expectation. One other line of enquiry still remains open to
us: namely, whether pure reason may not also be met with
in the practical sphere, and whether it may not there conduct
us to ideas which reach to those highest ends of pure reason
that we have just stated, and whether, therefore, reason may
not be able to supply to us from the standpoint of its practical
interest what it altogether refuses to supply in respect of its
speculative interest. 
All the interests of my reason, speculative as well as
practical, combine in the three following questions:
1. What can I know?
2. What ought I to do?
3. What may I hope?
The first question is merely speculative. We have, as I
flatter myself, exhausted all the possible answers to it, and at
last have found the answer with which reason must perforce
content itself, and with which, so long as it takes no account of
the practical, it has also good cause to be satisfied. But from
the two great ends to which the whole endeavour of pure
reason was really directed, we have remained just as far re-
moved as if through love of ease we had declined this labour
of enquiry at the very outset. So far, then, as knowledge is
concerned, this much, at least, is certain and definitively
established, that in respect of these two latter problems, know-
ledge is unattainable by us. 
The second question is purely practical. As such it can
P 636
indeed come within the scope of pure reason, but even so is not
transcendental but moral, and cannot, therefore, in and by
itself, form a proper subject for treatment in this Critique. 
The third question -- If I do what I ought to do, what may
I then hope? -- is at once practical and theoretical, in such
fashion that the practical serves only as a clue that leads us to
the answer to the theoretical question, and when this is followed
out, to the speculative question. For all hoping is directed to
happiness, and stands in the same relation to the practical and
the law of morality as knowing and the law of nature to the
theoretical knowledge of things. The former arrives finally
at the conclusion that something is (which determines the
ultimate possible end) because something ought to happen;
the latter, that something is (which operates as the supreme
cause) because something happens. 
Happiness is the satisfaction of all our desires, extensively,
in respect of their manifoldness, intensively, in respect of
their degree, and protensively, in respect of their duration. 
The practical law, derived from the motive of happiness, I
term pragmatic (rule of prudence), and that law, if there is
such a law, which has no other motive than worthiness of
being happy, I term moral (law of morality). The former
advises us what we have to do if we wish to achieve happiness;
the latter dictates to us how we must behave in order to de-
serve happiness. The former is based on empirical principles;
for only by means of experience can I know what desires there
are which call for satisfaction; or what those natural causes
are which are capable of satisfying them. The latter takes no
account of desires, and the natural means of satisfying them,
and considers only the freedom of a rational being in general,
and the necessary conditions under which alone this freedom
can harmonise with a distribution of happiness that is made
in accordance with principles. This latter law can therefore be
based on mere ideas of pure reason, and known a priori. 
 I assume that there really are pure moral laws which de-
termine completely a priori (without regard to empirical
motives, that is, to happiness) what is and is not to be done,
that is, which determine the employment of the freedom of a
rational being in general; and that these laws command in an
absolute manner (not merely hypothetically, on the supposi-
P 637
tion of other empirical ends), and are therefore in every respect
necessary. I am justified in making this assumption, in that I
can appeal not only to the proofs employed by the most en-
lightened moralists, but to the moral judgment of every man,
in so far as he makes the effort to think such a law clearly. 
Pure reason, then, contains, not indeed in its speculative
employment, but in that practical employment which is also
moral, principles of the possibility of experience, namely, of
such actions as, in accordance with moral precepts, might be
met with in the history of mankind. For since reason com-
mands that such actions should take place, it must be possible
for them to take place. Consequently, a special kind of system-
atic unity, namely the moral, must likewise be possible. 
We have indeed found that the systematic unity of nature
cannot be proved in accordance with speculative principles
of reason. For although reason does indeed have causality in
respect of freedom in general, it does not have causality in
respect of nature as a whole; and although moral principles
of reason can indeed give rise to free actions, they cannot give
rise to laws of nature. Accordingly it is in their practical,
meaning thereby their moral, employment, that the principles
of pure reason have objective reality. 
I entitle the world a moral world, in so far as it may be in
accordance with all moral laws; and this is what by means of
the freedom of the rational being it can be, and what according
to the necessary laws of morality it ought to be. Owing to our
here leaving out of account all conditions (ends) and even all
the special difficulties to which morality is exposed (weakness
or depravity of human nature), this world is so far thought as
an intelligible world only. To this extent, therefore, it is a
mere idea, though at the same time a practical idea, which
really can have, as it also ought to have, an influence upon the
sensible world, to bring that world, so far as may be possible,
into conformity with the idea. The idea of a moral world has,
therefore, objective reality, not as referring to an object of an
intelligible intuition (we are quite unable to think any such
object), but as referring to the sensible world, viewed, however,
as being an object of pure reason in its practical employ-
ment, that is, as a corpus mysticum of the rational beings in it,
so far as the free will of each being is, under moral laws, in
P 638
complete systematic unity with itself and with the freedom
of every other. 
This is the answer to the first of the two questions of pure
reason that concern its practical interest: -- Do that through
which thou becomest worthy to be happy. The second question
is: -- If I so behave as not to be unworthy of happiness, may I
hope thereby to obtain happiness? In answering this question
we have to consider whether the principles of pure reason,
which prescribe the law a priori, likewise connect this hope
necessarily with it. 
I maintain that just as the moral principles are necessary
according to reason in its practical employment, it is in the
view of reason, in the field of its theoretical employment, no
less necessary to assume that everyone has ground to hope
for happiness in the measure in which he has rendered himself
by his conduct worthy of it, and that the system of morality
is therefore inseparably -- though only in the idea of pure
reason -- bound up with that of happiness. 
Now in an intelligible world, that is, in the moral world, in
the concept of which we leave out of account all the hindrances
to morality (the desires), such a system, in which happiness is
bound up with and proportioned to morality, can be con-
ceived as necessary, inasmuch as freedom, partly inspired and
partly restricted by moral laws, would itself be the cause of
general happiness, since rational beings, under the guidance
of such principles, would themselves be the authors both of
their own enduring well-being and of that of others. But such
a system of self-rewarding morality is only an idea, the carry-
ing out of which rests on the condition that everyone does
what he ought, that is, that all the actions of rational beings
take place just as if they had proceeded from a supreme will
that comprehends in itself, or under itself, all private wills. 
But since the moral law remains binding for every one in the
use of his freedom, even although others do not act in con-
formity with the law, neither the nature of the things of the
world nor the causality of the actions themselves and their
relation to morality determine how the consequences of these
actions will be related to happiness. The alleged necessary
connection of the hope of happiness with the necessary en-
deavour to render the self worthy of happiness cannot there-
P 639
fore be known through reason. It can be counted upon only if
a Supreme Reason, that governs according to moral rules, be
likewise posited as underlying nature as its cause. 
The idea of such an intelligence in which the most perfect
moral will, united with supreme blessedness, is the cause of all
happiness in the world -- so far as happiness stands in exact re-
lation with morality, that is, with worthiness to be happy -- I
entitle the ideal of the supreme good. It is, therefore, only in the
ideal of the supreme original good that pure reason can find
the ground of this connection, which is necessary from the prac-
tical point of view, between the two elements of the supreme
derivative good -- the ground, namely, of an intelligible, that is,
moral world. Now since we are necessarily constrained by reason
to represent ourselves as belonging to such a world, while the
senses present to us nothing but a world of appearances, we
must assume that moral world to be a consequence of our con-
duct in the world of sense (in which no such connection be-
tween worthiness and happiness is exhibited), and therefore to
be for us a future world. Thus God and a future life are two
postulates which, according to the principles of pure reason,
are inseparable from the obligation which that same reason
imposes upon us. 
Morality, by itself, constitutes a system. Happiness, how-
ever, does not do so, save in so far as it is distributed in exact
proportion to morality. But this is possible only in the intel-
ligible world, under a wise Author and Ruler. Such a Ruler,
together with life in such a world, which we must regard as a
future world, reason finds itself constrained to assume; other-
wise it would have to regard the moral laws as empty figments
of the brain, since without this postulate the necessary conse-
quence which it itself connects with these laws could not
follow. Hence also everyone regards the moral laws as com-
mands; and this the moral laws could not be if they did not
connect a priori suitable consequences with their rules, and
thus carry with them promises and threats. But this again they
could not do, if they did not reside in a necessary being, as the
supreme good, which alone can make such a purposive unit
Leibniz entitled the world, in so far as we take account
only of the rational beings in it, and of their connection ac-
P 640
cording to moral laws under the government of the supreme
good, the kingdom of grace, distinguishing it from the king-
dom of nature, in which these rational beings do indeed stand
under moral laws, but expect no other consequences from
their actions than such as follow in accordance with the course
of nature in our world of sense. To view ourselves, therefore, as
in the world of grace, where all happiness awaits us, except in so
far as we ourselves limit our share in it through being unworthy
of happiness, is, from the practical standpoint, a necessary idea
of reason. 
Practical laws, in so far as they are subjective grounds of
actions, that is, subjective principles, are entitled maxims. The
estimation of morality, in regard to its purity and consequences,
is effected in accordance with ideas, the observance of its laws
in accordance with maxims. 
It is necessary that the whole course of our life be sub-
ject to moral maxims; but it is impossible that this should
happen unless reason connects with the moral law, which is a
mere idea, an operative cause which determines for such con-
duct as is in accordance with the moral law an outcome, either
in this or in another life, that is in exact conformity with our
supreme ends. Thus without a God and without a world in-
visible to us now but hoped for, the glorious ideas of morality
are indeed objects of approval and admiration, but not springs
of purpose and action. For they do not fulfil in its complete-
ness that end which is natural to every rational being and
which is determined a priori, and rendered necessary, by that
same pure reason. 
Happiness, taken by itself, is, for our reason, far from
being the complete good. Reason does not approve happiness
(however inclination may desire it) except in so far as it is united
with worthiness to be happy, that is, with moral conduct. 
Morality, taken by itself, and with it, the mere worthiness to
be happy, is also far from being the complete good. To make
the good complete, he who behaves in such a manner as not to
be unworthy of happiness must be able to hope that he will
participate in happiness. Even the reason that is free from all
private purposes, should it put itself in the place of a being that
had to distribute all happiness to others, cannot judge other-
wise; for in the practical idea both elements are essentially
P 641
connected, though in such a manner that it is the moral dis-
position which conditions and makes possible the participation
in happiness, and not conversely the prospect of happiness
that makes possible the moral disposition. For in the latter
case the disposition would not be moral, and therefore would
not be worthy of complete happiness -- happiness which in
the view of reason allows of no limitation save that which
arises from our own immoral conduct. 
Happiness, therefore, in exact proportion with the morality
of the rational beings who are thereby rendered worthy of it,
alone constitutes the supreme good of that world wherein, in
accordance with the commands of a pure but practical reason,
we are under obligation to place ourselves. This world is in-
deed an intelligible world only, since the sensible world holds
out no promise that any such systematic unity of ends can
arise from the nature of things. Nor is the reality of this unity
based on anything else than the postulate of a supreme ori-
ginal good. In a supreme good, thus conceived, self-subsistent
reason, equipped with all the sufficiency of a supreme cause,
establishes, maintains, and completes the universal order of
things, according to the most perfect design -- an order which
in the world of sense is in large part concealed from us. 
This moral theology has the peculiar advantage over
speculative theology that it inevitably leads to the concept of
a sole, all-perfect, and rational primordial being, to which
speculative theology does not, on objective grounds, even so
much as point the way, and as to the existence of which it is
still less capable of yielding any conviction. For neither in
transcendental nor in natural theology, however far reason
may carry us, do we find any considerable ground for assum-
ing only some one single being which we should be justi-
fied in placing prior to all natural causes, and upon which
we might make them in all respects dependent. On the
other hand, if we consider from the point of view of moral
unity, as a necessary law of the world, what the cause must
be that can alone give to this law its appropriate effect, and
so for us obligatory force, we conclude that there must be
one sole supreme will, which comprehends all these laws in
itself. For how, under different wills, should we find complete
P 642
unity of ends. This Divine Being must be omnipotent, in
order that the whole of nature and its relation to morality
in the world may be subject to his will; omniscient, that
He may know our innermost sentiments and their moral
worth; omnipresent, that He may be immediately at hand for
the satisfying of every need which the highest good demands;
eternal, that this harmony of nature and freedom may never
fail, etc. 
But this systematic unity of ends in this world of intelli-
gences -- a world which is indeed, as mere nature, a sensible
world only, but which, as a system of freedom, can be entitled
an intelligible, that is, a moral world (regnum gratiae) -- leads in-
evitably also to the purposive unity of all things, which constitute
this great whole, in accordance with universal laws of nature (just
as the former unity is in accordance with universal and neces-
sary laws of morality), and thus unites the practical with the
speculative reason. The world must be represented as having
originated from an idea if it is to be in harmony with that em-
ployment of reason without which we should indeed hold our-
selves to be unworthy of reason, namely, with the moral em-
ployment -- which is founded entirely on the idea of the supreme
good. In this way all investigation of nature tends to take the
form of a system of ends, and in its widest extension becomes a
physico-theology. But this, as it has its source in the moral order,
as a unity grounded in freedom's own essential nature, and not
accidentally instituted through external commands, connects
the purposiveness of nature with grounds which must be
inseparably connected a priori with the inner possibility of
things, and so leads to a transcendental theology -- a theology
which takes the ideal of supreme ontological perfection as a
principle of systematic unity. And since all things have their
origin in the absolute necessity of the one primordial being,
that principle connects them in accordance with universal and
necessary laws of nature. 
What use can we make of our understanding, even in re-
spect of experience, if we do not propose ends to ourselves? 
But the highest ends are those of morality, and these we can
know only as they are given us by pure reason. But though
provided with these, and employing them as a clue, we cannot
make use of the knowledge of nature in any serviceable manner
P 643
in the building up of knowledge, unless nature has itself
shown unity of design. For without this unity we should our-
selves have no reason, inasmuch as there would be no school
for reason, and no fertilisation through objects such as might
afford materials for the necessary concepts. But the former
purposive unity is necessary, and founded on the will's own
essential nature, and this latter unity [of design in nature]
which contains the condition of its application in concreto,
must be so likewise. And thus the transcendental enlargement
of our knowledge, as secured through reason, is not to be
regarded as the cause, but merely as the effect of the practical
purposiveness which pure reason imposes upon us. 
Accordingly we find, in the history of human reason, that
until the moral concepts were sufficiently purified and deter-
mined, and until the systematic unity of their ends was under-
stood in accordance with these concepts and from necessary
principles, the knowledge of nature, and even a quite con-
siderable development of reason in many other sciences, could
give rise only to crude and incoherent concepts of the Deity,
or as sometimes happened resulted in an astonishing in-
difference in regard to all such matters. A greater preoccupa-
tion with moral ideas, which was rendered necessary by the
extraordinarily pure moral law of our religion, made reason
more acutely aware of its object, through the interest which it
was compelled to take in it. And this came about, independ-
ently of any influence exercised by more extended views of
nature or by correct and reliable transcendental insight (for
that has always been lacking). It was the moral ideas that gave
rise to that concept of the Divine Being which we now hold
to be correct -- and we so regard it not because speculative
reason convinces us of its correctness, but because it com-
pletely harmonises with the moral principles of reason. Thus it
is always only to pure reason, though only in its practical
employment, that we must finally ascribe the merit of having
connected with our highest interest a knowledge which reason
can think only, and cannot establish, and of having thereby
shown it to be, not indeed a demonstrated dogma, but a
postulate which is absolutely necessary in view of what are
reason's own most essential ends. 
P 644
But when practical reason has reached this goal, namely,
the concept of a sole primordial being as the supreme good,
it must not presume to think that it has raised itself above all
empirical conditions of its application, and has attained to an
immediate knowledge of new objects, and can therefore start
from this concept, and can deduce from it the moral laws
themselves. For it is these very laws that have led us, in virtue
of their inner practical necessity, to the postulate of a self-
sufficient cause, or of a wise Ruler of the world, in order that
through such agency effect may be given to them. We may
not, therefore, in reversal of such procedure, regard them as
accidental and as derived from the mere will of the Ruler,
especially as we have no conception of such a will, except as
formed in accordance with these laws. So far, then, as prac-
tical reason has the right to serve as our guide, we shall not
look upon actions as obligatory because they are the commands
of God, but shall regard them as divine commands because
we have an inward obligation to them. We shall study freedom
according to the purposive unity that is determined in accord-
ance with the principles of reason, and shall believe ourselves
to be acting in conformity with the divine will in so far only
as we hold sacred the moral law which reason teaches us from
the nature of the actions themselves; and we shall believe that
we can serve that will only by furthering what is best in the
world, alike in ourselves and in others. Moral theology is thus
of immanent use only. It enables us to fulfil our vocation in
this present world by showing us how to adapt ourselves to the
system of all ends, and by warning us against the fanaticism,
and indeed the impiety, of abandoning the guidance of a
morally legislative reason in the right conduct of our lives, in
order to derive guidance directly from the idea of the Supreme
Being. For we should then be making a transcendent em-
ployment of moral theology; and that, like a transcendent use
of pure speculation, must pervert and frustrate the ultimate
ends of reason. 
P 645
Section 3
The holding of a thing to be true is an occurrence in our
understanding which, though it may rest on objective grounds,
also requires subjective causes in the mind of the individual
who makes the judgment. If the judgment is valid for everyone,
provided only he is in possession of reason, its ground is ob-
jectively sufficient, and the holding of it to be true is entitled
conviction. If it has its ground only in the special character of
the subject, it is entitled persuasion. 
Persuasion is a mere illusion, because the ground of the
judgment, which lies solely in the subject, is regarded as objec-
tive. Such a judgment has only private validity, and the hold-
ing of it to be true does not allow of being communicated. 
But truth depends upon agreement with the object, and in re-
spect of it the judgments of each and every understanding
must therefore be in agreement with each other (consentientia
uni tertio, consentiunt inter se). The touchstone whereby we
decide whether our holding a thing to be true is conviction
or mere persuasion is therefore external, namely, the possi-
bility of communicating it and of finding it to be valid for all
human reason. For there is then at least a presumption that
the ground of the agreement of all judgments with each other,
notwithstanding the differing characters of individuals, rests
upon the common ground, namely, upon the object, and that
it is for this reason that they are all in agreement with the
object -- the truth of the judgment being thereby proved. 
So long, therefore, as the subject views the judgment merely
as an appearance of his mind, persuasion cannot be subject-
ively distinguished from conviction. The experiment, how-
ever, whereby we test upon the understanding of others
whether those grounds of the judgment which are valid for us
have the same effect on the reason of others as on our own, is
a means, although only a subjective means, not indeed of pro-
ducing conviction, but of detecting any merely private validity
P 646
in the judgment, that is, anything in it which is mere per-
If, in addition, we can specify the subjective causes of the
judgment, which we have taken as being its objective grounds,
and can thus explain the deceptive judgment as an event in
our mind, and can do so without having to take account of the
character of the object, we expose the illusion and are no longer
deceived by it, although always still in some degree liable to
come under its influence, in so far as the subjective cause of
the illusion is inherent in our nature. 
I cannot assert anything, that is, declare it to be a judg-
ment necessarily valid for everyone, save as it gives rise to
conviction. Persuasion I can hold to on my own account, if it
so pleases me, but I cannot, and ought not, to profess to
impose it as binding on anyone but myself. 
The holding of a thing to be true, or the subjective validity
of the judgment, in its relation to conviction (which is at the
same time objectively valid), has the following three degrees:
opining, believing, and knowing. Opining is such holding of a
judgment as is consciously insufficient, not only objectively,
but also subjectively. If our holding of the judgment be only
subjectively sufficient, and is at the same time taken as being
objectively insufficient, we have what is termed believing. 
Lastly, when the holding of a thing to be true is sufficient
both subjectively and objectively, it is knowledge. The sub-
jective sufficiency is termed conviction (for myself), the
objective sufficiency is termed certainty (for everyone). 
There is no call for me to spend further time on the ex-
planation of such easily understood terms. 
I must never presume to opine, without knowing at least
something by means of which the judgment, in itself merely
problematic, secures connection with truth, a connection
which, although not complete, is yet more than arbitrary
fiction. Moreover, the law of such a connection must be cer-
tain. For if, in respect of this law also, I have nothing but
opinion, it is all merely a play of the imagination, without the
least relation to truth. Again, opining is not in any way per-
missible in judging by means of pure reason. For since such
judging is not based on grounds of experience, but being in
P 647
every case necessary has all to be arrived at a priori, the prin-
ciple of the connection requires universality and necessity, and
therefore complete certainty; otherwise we should have no
guidance as to truth. Hence it is absurd to have an opinion
in pure mathematics; either we must know, or we must
abstain from all acts of judgment. It is so likewise in the case
of the principles of morality, since we must not venture upon
an action on the mere opinion that it is allowed, but must
know it to be so. 
In the transcendental employment of reason, on the other
hand, while opining is doubtless too weak a term to be ap-
plicable, the term knowing is too strong. In the merely specu-
lative sphere we cannot therefore make any judgments what-
soever. For the subjective grounds upon which we may hold
something to be true, such as those which are able to produce
belief, are not permissible in speculative questions, inasmuch
as they do not hold independently of all empirical support,
and do not allow of being communicated in equal measure to
But it is only from a practical point of view that the theo-
retically insufficient holding of a thing to be true can be
termed believing. This practical point of view is either in
reference to skill or in reference to morality, the former being
concerned with optional and contingent ends, the latter with
ends that are absolutely necessary. 
Once an end is accepted, the conditions of its attainment
are hypothetically necessary. This necessity is subjectively,
but still only comparatively, sufficient, if I know of no other
conditions under which the end can be attained. On the other
hand, it is sufficient, absolutely and for everyone, if I know
with certainty that no one can have knowledge of any other
conditions which lead to the proposed end. In the former case
my assumption and the holding of certain conditions to be
true is a merely contingent belief; in the latter case it is a
necessary belief. The physician must do something for a
patient in danger, but does not know the nature of his illness. 
He observes the symptoms, and if he can find no more likely
alternative, judges it to be a case of phthisis. Now even in his
own estimation his belief is contingent only; another observer
P 648
might perhaps come to a sounder conclusion. Such contingent
belief, which yet forms the ground for the actual employment
of means to certain actions, I entitle pragmatic belief. 
The usual touchstone, whether that which someone asserts
is merely his persuasion -- or at least his subjective conviction,
that is, his firm belief -- is betting. It often happens that some-
one propounds his views with such positive and uncompromis-
ing assurance that he seems to have entirely set aside all
thought of possible error. A bet disconcerts him. Sometimes
it turns out that he has a conviction which can be estimated at
a value of one ducat, but not of ten. For he is very willing to
venture one ducat, but when it is a question of ten he becomes
aware, as he had not previously been, that it may very well be
that he is in error. If, in a given case, we represent ourselves
as staking the happiness of our whole life, the triumphant
tone of our judgment is greatly abated; we become extremely
diffident, and discover for the first time that our belief does not
reach so far. Thus pragmatic belief always exists in some
specific degree, which, according to differences in the interests
at stake, may be large or may be small. 
But in many cases, when we are dealing with an object
about which nothing can be done by us, and in regard to which
our judgment is therefore purely theoretical, we can conceive
and picture to ourselves an attitude for which we regard
ourselves as having sufficient grounds, while yet there is no
existing means of arriving at certainty in the matter. Thus
even in purely theoretical judgments there is an analogon
of practical judgments, to the mental entertaining of which
the term 'belief' is appropriate, and which we may entitle
doctrinal belief. I should be ready to stake my all on the con-
tention -- were it possible by means of any experience to settle
the question -- that at least one of the planets which we see is
inhabited. Hence I say that it is not merely opinion, but a
strong belief, on the correctness of which I should be prepared
to run great risks, that other worlds are inhabited. 
 Now we must admit that the doctrine of the existence of
God belongs to doctrinal belief. For as regards theoretical
knowledge of the world, I can cite nothing which necessarily
presupposes this thought as the condition of my explanations
P 649
of the appearances exhibited by the world, but rather am
bound so to employ my reason as if everything were mere
nature. Purposive unity is, however, so important a condition
of the application of reason to nature that I cannot ignore it,
especially as experience supplies me so richly with examples of
it. But I know no other condition under which this unity can sup-
ply me with guidance in the investigation of nature, save only
the postulate that a supreme intelligence has ordered all things
in accordance with the wisest ends. Consequently, as a condi-
tion of what is indeed a contingent, but still not unimportant
purpose, namely, to have guidance in the investigation of
nature, we must postulate a wise Author of the world. More-
over, the outcome of my attempts [in explanation of nature]
so frequently confirms the usefulness of this postulate, while
nothing decisive can be cited against it, that I am saying much
too little if I proceed to declare that I hold it merely as an
opinion. Even in this theoretical relation it can be said that I
firmly believe in God. This belief is not, therefore, strictly
speaking, practical; it must be entitled a doctrinal belief to
which the theology of nature (physico-theology) must always
necessarily give rise. In view of the magnificent equipment of
our human nature, and the shortness of life so ill-suited to the
full exercise of our powers, we can find in this same divine
wisdom a no less sufficient ground for a doctrinal belief in
the future life of the human soul. 
In such cases the expression of belief is, from the objective
point of view, an expression of modesty, and yet at the same
time, from the subjective point of view, an expression of the
firmness of our confidence. Were I even to go the length of
describing the merely theoretical holding of the belief as an
hypothesis which I am justified in assuming, I should thereby
be pledging myself to have a more adequate concept of the
character of a cause of the world and of the character of
another world than I am really in a position to supply. For
if I assume anything, even merely as an hypothesis, I must
at least know so much of its properties that I require to
assume, not its concept, but only its existence. The term
'belief' refers only to the guidance which an idea gives me,
and to its subjective influence in that furthering of the activi-
ties of my reason which confirms me in the idea, and which
P 650
yet does so without my being in a position to give a specu-
lative account of it. 
But the merely doctrinal belief is somewhat lacking in
stability; we often lose hold of it, owing to the speculative
difficulties which we encounter, although in the end we
always inevitably return to it. 
It is quite otherwise with moral belief. For here it is abso-
lutely necessary that something must happen, namely, that I
must in all points conform to the moral law. The end is here
irrefragably established, and according to such insight as I
can have, there is only one possible condition under which this
end can connect with all other ends, and thereby have prac-
tical validity, namely, that there be a God and a future world. 
I also know with complete certainty that no one can be ac-
quainted with any other conditions which lead to the same
unity of ends under the moral law. Since, therefore, the moral
precept is at the same time my maxim (reason prescribing that
it should be so), I inevitably believe in the existence of God
and in a future life, and I am certain that nothing can shake
this belief, since my moral principles would thereby be them-
selves overthrown, and I cannot disclaim them without be-
coming abhorrent in my own eyes. 
Thus even after reason has failed in all its ambitious at-
tempts to pass beyond the limits of all experience, there is
still enough left to satisfy us, so far as our practical stand-
point is concerned. No one, indeed, will be able to boast
that he knows that there is a God, and a future life; if he
knows this, he is the very man for whom I have long [and
vainly] sought. All knowledge, if it concerns an object of
mere reason, can be communicated; and I might therefore
hope that under his instruction my own knowledge would be
extended in this wonderful fashion. No, my conviction is not
logical, but moral certainty; and since it rests on subjective
grounds (of the moral sentiment), I must not even say, 'It is
morally certain that there is a God, etc. ', but 'I am morally
certain, etc. ' In other words, belief in a God and in another
world is so interwoven with my moral sentiment that as there
is little danger of my losing the latter, there is equally little
cause for fear that the former can ever be taken from me. 
P 651
The only point that may seem questionable is the basing
of this rational belief on the assumption of moral sentiments. 
If we leave these aside, and take a man who is completely
indifferent with regard to moral laws, the question propounded
by reason then becomes merely a problem for speculation,
and can, indeed, be supported by strong grounds of analogy,
but not by such as must compel the most stubborn scepticism
to give way. But in these questions no man is free from all
interest. For although, through lack of good sentiments, he
may be cut off from moral interest, still even in this case
enough remains to make him fear the existence of a God
and a future life. Nothing more is required for this than that
he at least cannot pretend that there is any certainty that
there is no such being and no such life. Since that would have
to be proved by mere reason, and therefore apodeictically, he
would have to prove the impossibility of both, which assuredly
no one can reasonably undertake to do. This may therefore
serve as negative belief, which may not, indeed, give rise to
morality and good sentiments, but may still give rise to an
analogon of these, namely, a powerful check upon the out-
break of evil sentiments. 
 But, it will be said, is this all that pure reason acheives
in opening up prospects beyond the limits of experience? 
Nothing more than two articles of belief? Surely the common
understanding could have achieved as much, without appeal-
ing to philosophers for counsel in the matter. 
I shall not here dwell upon the service which philosophy
has done to human reason through the laborious efforts of its
criticism, granting even that in the end it should turn out to
be merely negative; something more will be said on this point
in the next section.
++ The human mind (as, I likewise believe, must necessarily be the
case with every rational being) takes a natural interest in morality,
although this interest is not undivided and practically preponderant. 
If we confirm and increase this interest, we shall find reason very
teachable and in itself more enlightened as regards the uniting of the
speculative with the practical interest. But if we do not take care that
we first make men good, at least in some measure good, we shall never
make honest believers of them. 
P 651
But I may at once reply: Do you really
require that a mode of knowledge which concerns all men
P 652
should transcend the common understanding, and should only
be revealed to you by philosophers? Precisely what you find
fault with is the best confirmation of the correctness of the
above assertions. For we have thereby revealed to us, what
could not at the start have been foreseen, namely, that in
matters which concern all men without distinction nature is
not guilty of any partial distribution of her gifts, and that in
regard to the essential ends of human nature the highest
philosophy cannot advance further than is possible under the
guidance which nature has bestowed even upon the most
ordinary understanding. 
P 653
BY an architectonic I understand the art of constructing sys-
tems. As systematic unity is what first raises ordinary know-
ledge to the rank of science, that is, makes a system out of a
mere aggregate of knowledge, architectonic is the doctrine of
the scientific in our knowledge, and therefore necessarily
forms part of the doctrine of method. 
In accordance with reason's legislative prescriptions, our
diverse modes of knowledge must not be permitted to be a
mere rhapsody, but must form a system. Only so can they
further the essential ends of reason. By a system I understand
the unity of the manifold modes of knowledge under one idea. 
This idea is the concept provided by reason -- of the form of a
whole -- in so far as the concept determines a priori not only
the scope of its manifold content, but also the positions which
the parts occupy relatively to one another. The scientific con-
cept of reason contains, therefore, the end and the form of that
whole which is congruent with this requirement. The unity of
the end to which all the parts relate and in the idea of which
they all stand in relation to one another, makes it possible for
us to determine from our knowledge of the other parts whether
any part be missing, and to prevent any arbitrary addition, or
in respect of its completeness any indeterminateness that does
not conform to the limits which are thus determined a priori. 
The whole is thus an organised unity (articulatio), and not an
aggregate (coacervatio). It may grow from within (per intus-
susceptionem), but not by external addition (per appositionem). 
It is thus like an animal body, the growth of which is not by
P 654
the addition of a new member, but by the rendering of each
member, without change of proportion, stronger and more
effective for its purposes. 
The idea requires for its realisation a schema, that is, a
constituent manifold and an order of its parts, both of which
must be determined a priori from the principle defined by its
end. The schema, which is not devised in accordance with an
idea, that is, in terms of the ultimate aim of reason, but em-
pirically in accordance with purposes that are contingently
occasioned (the number of which cannot be foreseen) yields
technical unity; whereas the schema which originates from an
idea (in which reason propounds the ends a priori, and does
not wait for them to be empirically given) serves as the basis
of architectonic unity. Now that which we call science, the
schema of which must contain the outline (monogramma) and
the division of the whole into parts, in conformity with the
idea, that is, a priori, and in so doing must distinguish it with
certainty and according to principles from all other wholes, is
not formed in technical fashion, in view of the similarity of
its manifold constituents or of the contingent use of our know-
ledge in concreto for all sorts of optional external ends, but in
architectonic fashion, in view of the affinity of its parts and of
their derivation from a single supreme and inner end, through
which the whole is first made possible. 
No one attempts to establish a science unless he has an
idea upon which to base it. But in the working out of the
science the schema, nay even the definition which, at the start,
he first gave of the science, is very seldom adequate to his idea. 
For this idea lies hidden in reason, like a germ in which the
parts are still undeveloped and barely recognisable even under
microscopic observation. Consequently, since sciences are de-
vised from the point of view of a certain universal interest,
we must not explain and determine them according to the
description which their founder gives of them, but in con-
formity with the idea which, out of the natural unity of the
parts that we have assembled, we find to be grounded in
reason itself. For we shall then find that its founder, and often
even his latest successors, are groping for an idea which they
have never succeeded in making clear to themselves, and that
P 655
consequently they have not been in a position to determine the
proper content, the articulation (systematic unity), and limits
of the science. 
It is unfortunate that only after we have spent much time
in the collection of materials in somewhat random fashion at
the suggestion of an idea lying hidden in our minds, and after
we have, indeed, over a long period assembled the materials in
a merely technical manner, does it first become possible for
us to discern the idea in a clearer light, and to devise a whole
architectonically in accordance with the ends of reason. 
Systems seem to be formed in the manner of lowly organisms
through a generatio aequivoca from the mere confluence of
assembled concepts, at first imperfect, and only gradually
attaining to completeness, although they one and all have had
their schema, as the original germ, in the sheer self-develop-
ment of reason. Hence, not only is each system articulated in
accordance with an idea, but they are one and all organically
united in a system of human knowledge, as members of one
whole, and so as admitting of an architectonic of all human
knowledge, which, at the present time, in view of the great
amount of material that has been collected, or which can be
obtained from the ruins of ancient systems, is not only pos-
sible, but would not indeed be difficult. We shall content our-
selves here with the completion of our task, namely, merely to
outline the architectonic of all knowledge arising from pure
reason; and in doing so we shall begin from the point at which
the common root of our faculty of knowledge divides and
throws out two stems, one of which is reason. By reason I here
understand the whole higher faculty of knowledge, and am
therefore contrasting the rational with the empirical. 
If I abstract from all the content of knowledge, objectively
regarded, then all knowledge, subjectively regarded, is either
historical or rational. Historical knowledge is cognitio ex datis;
rational knowledge is cognitio ex principiis. However a mode
of knowledge may originally be given, it is still, in relation to
the individual who possesses it, simply historical, if he knows
only so much of it as has been given to him from outside (and
this in the form in which it has been given to him), whether
through immediate experience or narration, or (as in the case
P 656
of general knowledge) through instruction. Anyone, therefore,
who has learnt (in the strict sense of that term) a system of
philosophy, such as that of Wolff, although he may have all
its principles, explanations, and proofs, together with the
formal divisions of the whole body of doctrine, in his head,
and, so to speak, at his fingers' ends, has no more than a
complete historical knowledge of the Wolffian philosophy. 
He knows and judges only what has been given him. If we
dispute a definition, he does not know whence to obtain
another. He has formed his mind on another's, and the imi-
tative faculty is not itself productive. In other words, his
knowledge has not in him arisen out of reason, and although,
objectively considered, it is indeed knowledge due to reason,
it is yet, in its subjective character, merely historical. He has
grasped and kept; that is, he has learnt well, and is merely
a plaster-cast of a living man. Modes of rational knowledge
which are rational objectively (that is, which can have their
first origin solely in human reason) can be so entitled sub-
jectively also, only when they have been derived from uni-
versal sources of reason, that is, from principles -- the sources
from which there can also arise criticism, nay, even the rejec-
tion of what has been learnt. 
All knowledge arising out of reason is derived either from
concepts or from the construction of concepts. The former is
called philosophical, the latter mathematical. I have already
treated of the fundamental difference between these two modes
of knowledge in the first chapter [of this Transcendental Doc-
trine of Method]. Knowledge [as we have just noted] can be
objectively philosophical, and yet subjectively historical, as is
the case with most novices, and with all those who have never
looked beyond their School, and who remain novices all their
lives. But it is noteworthy that mathematical knowledge, in its
subjective character, and precisely as it has been learned, can
also be regarded as knowledge arising out of reason, and that
there is therefore in regard to mathematical knowledge no such
distinction as we have drawn in the case of philosophical know-
ledge. This is due to the fact that the sources of knowledge,
from which alone the teacher can derive his knowledge, lie no-
where but in the essential and genuine principles of reason, and
consequently cannot be acquired by the novice from any other
P 657
source, and cannot be disputed; and this, in turn, is owing to
the fact that the employment of reason is here in concreto only,
although likewise a priori, namely, in intuition which is pure,
and which precisely on that account is infallible, excluding
all illusion and error. Mathematics, therefore, alone of all the
sciences (a priori) arising from reason, can be learned; philo-
sophy can never be learned, save only in historical fashion;
as regards what concerns reason, we can at most learn to
Philosophy is the system of all philosophical knowledge. 
If we are to understand by it the archetype for the estimation
of all attempts at philosophising, and if this archetype is to
serve for the estimation of each subjective philosophy, the struc-
ture of which is often so diverse and liable to alteration, it must
be taken objectively. Thus regarded, philosophy is a mere idea
of a possible science which nowhere exists in concreto, but to
which, by many different paths, we endeavour to approximate,
until the one true path, overgrown by the products of sen-
sibility, has at last been discovered, and the image, hitherto
so abortive, has achieved likeness to the archetype, so far as
this is granted to [mortal] man. Till then we cannot learn
philosophy; for where is it, who is in possession of it, and how
shall we recognise it? We can only learn to philosophise, that
is, to exercise the talent of reason, in accordance with its
universal principles, on certain actually existing attempts at
philosophy, always, however, reserving the right of reason to
investigate, to confirm, or to reject these principles in their
very sources. 
Hitherto the concept of philosophy has been a merely schol-
astic concept -- a concept of a system of knowledge which is
sought solely in its character as a science, and which has there-
fore in view only the systematic unity appropriate to science,
and consequently no more than the logical perfection of know-
ledge. But there is likewise another concept of philosophy, a
conceptus cosmicus, which has always formed the real basis of
the term 'philosophy', especially when it has been as it were
personified and its archetype represented in the ideal philo-
sopher. On this view, philosophy is the science of the relation
of all knowledge to the essential ends of human reason
P 658
(teleologia rationis humanae), and the philosopher is not an
artificer in the field of reason, but himself the lawgiver of
human reason. In this sense of the term it would be very
vainglorious to entitle oneself a philosopher, and to pretend
to have equalled the pattern which exists in the idea alone. 
The mathematician, the natural philosopher, and the
logician, however successful the two former may have been in
their advances in the field of rational knowledge, and the two
latter more especially in philosophical knowledge, are yet only
artificers in the field of reason. There is a teacher, [conceived]
in the ideal, who sets them their tasks, and employs them as
instruments, to further the essential ends of human reason. 
Him alone we must call philosopher; but as he nowhere exists,
while the idea of his legislation is to be found in that reason
with which every human being is endowed, we shall keep
entirely to the latter, determining more precisely what philo-
sophy prescribes as regards systematic unity, in accordance
with this cosmical concept, from the standpoint of its essential
Essential ends are not as such the highest ends; in view
of the demand of reason for complete systematic unity, only
one of them can be so described. Essential ends are therefore
either the ultimate end or subordinate ends which are neces-
sarily connected with the former as means. The former is no
other than the whole vocation of man, and the philosophy
which deals with it is entitled moral philosophy. On account
of this superiority which moral philosophy has over all other
occupations of reason, the ancients in their use of the term
'philosopher' always meant, more especially, the moralist; and
even at the present day we are led by a certain analogy to
entitle anyone a philosopher who appears to exhibit self-control
under the guidance of reason, however limited his knowledge
may be. 
++ By 'cosmical concept' [Weltbegriff] is here meant the concept
which relates to that in which everyone necessarily has an interest;
and accordingly if a science is to be regarded merely as one of the
disciplines designed in view of certain optionally chosen ends, I must
determine it in conformity with scholastic concepts. 
P 658
The legislation of human reason (philosophy) has two
objects, nature and freedom, and therefore contains not only
P 659
the law of nature, but also the moral law, presenting them
at first in two distinct systems, but ultimately in one single
philosophical system. The philosophy of nature deals with all
that is, the philosophy of morals with that which ought to be. 
All philosophy is either knowledge arising out of pure
reason, or knowledge obtained by reason from empirical
principles. The former is termed pure, the latter empirical
The philosophy of pure reason is either a propaedeutic
(preparation), which investigates the faculty of reason in
respect of all its pure a priori knowledge, and is entitled
the science which exhibits in systematic connection the whole
body (true as well as illusory) of philosophical knowledge
arising out of pure reason, and which is entitled metaphysics. 
The title 'metaphysics' may also, however, be given to the
whole of pure philosophy, inclusive of criticism, and so as com-
prehending the investigation of all that can ever be known
a priori as well as the exposition of that which constitutes a
system of the pure philosophical modes of knowledge of this
type -- in distinction, therefore, from all empirical and from
all mathematical employment of reason. 
Metaphysics is divided into that of the speculative and that
of the practical employment of pure reason, and is there-
fore either metaphysics of nature or metaphysics of morals. 
The former contains all the principles of pure reason that
are derived from mere concepts (therefore excluding mathe-
matics), and employed in the theoretical knowledge of all
things; the latter, the principles which in a priori fashion
determine and make necessary all our actions. Now morality
is the only code of laws applying to our actions which can
be derived completely a priori from principles. Accordingly,
the metaphysics of morals is really pure moral philosophy,
with no underlying basis of anthropology or of other empirical
conditions. The term 'metaphysics', in its strict sense, is com-
monly reserved for the metaphysics of speculative reason. 
But as pure moral philosophy really forms part of this special
P 660
branch of human and philosophical knowledge derived from
pure reason, we shall retain for it the title 'metaphysics'. We
are not, however, at present concerned with it, and may there-
fore leave it aside. 
It is of the utmost importance to isolate the various modes
of knowledge according as they differ in kind and in origin,
and to secure that they be not confounded owing to the fact
that usually, in our employment of them, they are combined. 
What the chemist does in the analysis of substances, and
the mathematician in his special disciplines, is in still greater
degree incumbent upon the philosopher, that he may be able
to determine with certainty the part which belongs to each
special kind of knowledge in the diversified employment of the
understanding and its special value and influence. Human
reason, since it first began to think, or rather to reflect, has never
been able to dispense with a metaphysics; but also has never
been able to obtain it in a form sufficiently free from all foreign
elements. The idea of such a science is as old as speculative
human reason; and what rational being does not speculate,
either in scholastic or in popular fashion? It must be admitted,
however, that the two elements of our knowledge -- that
which is in our power completely a priori, and that which is
obtainable only a posteriori from experience -- have never been
very clearly distinguished, not even by professional thinkers,
and that they have therefore failed to bring about the delimita-
tion of a special kind of knowledge, and thereby the true idea
of the science which has preoccupied human reason so long and
so greatly. When metaphysics was declared to be the science
of the first principles of human knowledge, the intention was
not to mark out a quite special kind of knowledge, but only
a certain precedence in respect of generality, which was not
sufficient to distinguish such knowledge from the empirical. 
For among empirical principles we can distinguish some that
are more general, and so higher in rank than others; but
where in such a series of subordinated members -- a series in
which we do not distinguish what is completely a priori from
what is known only a posteriori -- are we to draw the line
which distinguishes the highest or first members from the
lower subordinate members? What should we say, if in the
P 661
reckoning of time we could distinguish the epochs of the
world only by dividing them into the first centuries and those
that follow? We should ask: Does the fifth, the tenth century,
etc. , belong with the first centuries? So in like manner I ask:
Does the concept of the extended belong to metaphysics? 
You answer, Yes. Then, that of body too? Yes. And that of
fluid body? You now become perplexed; for at this rate every-
thing will belong to metaphysics. It is evident, therefore, that
the mere degree of subordination (of the particular under
the general) cannot determine the limits of a science; in the
case under consideration, only complete difference of kind and
of origin will suffice. But the fundamental idea of metaphysics
was obscured on yet another side, owing to its exhibiting, as
a priori knowledge, a certain similarity to mathematics. 
Certainly they are related, in so far as they both have an
a priori origin; but when we bear in mind the difference
between philosophical and mathematical knowledge, namely,
that the one is derived from concepts, whereas in the other
we arrive at a priori judgments only through the construction
which has indeed always been in a manner felt but could
never be defined by means of any clear criteria. Thus it
has come about that since philosophers failed in the task of
developing even the idea of their science, they could have
no determinate end or secure guidance in the elaboration
of it, and, accordingly, in this arbitrarily conceived enter-
prise, ignorant as they were of the path to be taken, they have
always been at odds with one another as regards the dis-
coveries which each claimed to have made on his own separate
path, with the result that their science has been brought into
contempt, first among outsiders, and finally even among
All pure a priori knowledge, owing to the special faculty
of knowledge in which alone it can originate, has in itself a
peculiar unity; and metaphysics is the philosophy which has
as its task the statement of that knowledge in this systematic
unity. Its speculative part, which has especially appropriated
this name, namely, what we entitle metaphysics of nature, and
which considers everything in so far as it is (not that which
P 662
ought to be) by means of a priori concepts, is divided in the
following manner. 
Metaphysics, in the narrower meaning of the term, con-
sists of transcendental philosophy and physiology of pure
reason. The former treats only of the understanding and of
reason, in a system of concepts and principles which relate to
objects in general but take no account of objects that may be
given (Ontologia); the latter treats of nature, that is, of the
sum of given objects (whether given to the senses, or, if we will,
to some other kind of intuition) and is therefore physiology --
although only rationalis. The employment of reason in this
rational study of nature is either physical or hyperphysical,
or, in more adequate terms, is either immanent or transcen-
dent. The former is concerned with such knowledge of nature
as can be applied in experience (in concreto), the latter with
that connection of objects of experience which transcends
all experience. This transcendent physiology has as its object
either an inner connection or an outer connection, both, how-
ever, transcending possible experience. As dealing with an
inner connection it is the physiology of nature as a whole,
that is, the transcendental knowledge of the world; as dealing
with an outer connection, it is the physiology of the relation
of nature as a whole to a being above nature, that is to say,
it is the transcendental knowledge of God. 
Immanent physiology, on the other hand, views nature as
the sum of all objects of the senses, and therefore just as it is
given us, but solely in accordance with a priori conditions,
under which alone it can ever be given us. There are only two
kinds of such objects. Those of the outer senses, and so
their sum, corporeal nature. The object of inner sense,
the soul, and in accordance with our fundamental concepts of
it, thinking nature. The metaphysics of corporeal nature is
entitled physics; and as it must contain only the principles of
an a priori knowledge of it, rational physics. The metaphysics
of thinking nature is entitled psychology, and on the same
ground is to be understood as being only the rational know-
ledge of it. 
The whole system of metaphysics thus consists of four
main parts: (1) ontology; (2) rational physiology; (3) rational
cosmology; (4) rational theology. The second part, namely,
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the doctrine of nature as developed by pure reason, contains
two divisions physica rationalis and psychologia rationalis. 
The originative idea of a philosophy of pure reason itself
prescribes this division, which is therefore architectonic, in
accordance with the essential ends of reason, and not merely
technical, in accordance with accidentally observed simil-
arities, and so instituted as it were at haphazard. Accordingly
the division is also unchangeable and of legislative authority. 
There are, however, some points which may well seem doubt-
ful, and may weaken our conviction as to the legitimacy of
its claims. 
First of all, how can I expect to have knowledge a priori
(and therefore a metaphysics) of objects in so far as they are
given to our senses, that is, given in an a posteriori manner? 
And how is it possible to know the nature of things and
to arrive at a rational physiology according to principles
a priori?  The answer is this: we take nothing more from experi-
ence than is required to give us an object of outer or of inner
sense. The object of outer sense we obtain through the mere
concept of matter (impenetrable, lifeless extension), the object
of inner sense through the concept of a thinking being (in the
empirical inner representation, 'I think'). As to the rest, in the
whole metaphysical treatment of these objects, we must en-
tirely dispense with all empirical principles which profess to
add to these concepts any other more special experience, with
a view to our passing further judgments upon the objects. 
++ I must not be taken as meaning thereby what is commonly
called physica generalis; the latter is rather mathematics than phil-
osophy of nature. The metaphysics of nature is quite distinct from
mathematics. It is very far from enlarging our knowledge in the
fruitful manner of mathematics, but still is very important as yield-
ing a criticism of the pure knowledge of understanding in its
application to nature. For lack of it, even mathematicians, holding
to certain common concepts, which though common are yet in
fact metaphysical, have unconsciously encumbered their doctrine
of nature with hypotheses which vanish upon criticism of the prin-
ciples involved, without, however, doing the least injury to the
employment of mathematics -- employment which is quite indis-
pensable in this field. 
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Secondly, how are we to regard empirical psychology,
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which has always claimed its place in metaphysics, and from
which in our times such great things have been expected for
the advancement of metaphysics, the hope of succeeding by
a priori methods having been abandoned. I answer that it be-
longs where the proper (empirical) doctrine of nature belongs,
namely, by the side of applied philosophy, the a priori prin-
ciples of which are contained in pure philosophy; it is therefore
so far connected with applied philosophy, though not to be
confounded with it. Empirical psychology is thus completely
banished from the domain of metaphysics; it is indeed already
completely excluded by the very idea of the latter science. In
conformity, however, with scholastic usage we must allow it
some sort of a place (although as an episode only) in meta-
physics and this from economical motives, because it is not yet
so rich as to be able to form a subject of study by itself, and yet
is too important to be entirely excluded and forced to settle
elsewhere, in a neighbourhood that might well prove much
less congenial than that of metaphysics. Though it is but a
stranger it has long been accepted as a member of the house-
hold, and we allow it to stay for some time longer, until it is in
a position to set up an establishment of its own in a complete
anthropology, the pendant to the empirical doctrine of nature. 
Such, then, in general, is the idea of metaphysics. At first
more was expected from metaphysics than could reasonably be
demanded, and for some time it diverted itself with pleasant
anticipations. But these hopes having proved deceptive, it
has now fallen into general disrepute. The argument of our
Critique, taken as a whole, must have sufficiently convinced
the reader that although metaphysics cannot be the foundation
of religion, it must always continue to be a bulwark of it, and
that human reason, being by its very nature dialectical, can
never dispense with such a science, which curbs it, and by a
scientific and completely convincing self-knowledge, prevents
the devastations of which a lawless speculative reason would
otherwise quite inevitably be guilty in the field of morals as
well as in that of religion. We can therefore be sure that how-
ever cold or contemptuously critical may be the attitude of
those who judge a science not by its nature but by its acci-
dental effects, we shall always return to metaphysics as to a be-
loved one with whom we have had a quarrel. For here we are
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concerned with essential ends -- ends with which metaphysics
must ceaselessly occupy itself, either in striving for genuine
insight into them, or in refuting those who profess already to
have attained it. 
Metaphysics, alike of nature and of morals, and especially
that criticism of our adventurous and self-reliant reason which
serves as an introduction or propaedeutic to metaphysics,
alone properly constitutes what may be entitled philosophy,
in the strict sense of the term. Its sole preoccupation is wisdom;
and it seeks it by the path of science, which, once it has been
trodden, can never be overgrown, and permits of no wander-
ing. Mathematics, natural science, even our empirical know-
ledge, have a high value as means, for the most part, to con-
tingent ends, but also, in the ultimate outcome, to ends that
are necessary and essential to humanity. This latter service,
however, they can discharge only as they are aided by a know-
ledge through reason from pure concepts, which, however we
may choose to entitle it, is really nothing but metaphysics. 
For the same reason metaphysics is also the full and com-
plete development of human reason. Quite apart from its
influence, as science, in connection with certain specific ends
it is an indispensable discipline. For in dealing with reason it
treats of those elements and highest maxims which must form
the basis of the very possibility of some sciences, and of the
use of all. That, as mere speculation, it serves rather to prevent
errors than to extend knowledge, does not detract from its
value. On the contrary this gives it dignity and authority,
through that censorship which secures general order and har-
mony, and indeed the well-being of the scientific common-
wealth, preventing those who labour courageously and fruit-
fully on its behalf from losing sight of the supreme end, the
happiness of all mankind. 
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THIS title stands here only in order to indicate one remaining
division of the system, which future workers must complete. 
I content myself with casting a cursory glance, from a purely
transcendental point of view, namely, that of the nature of
pure reason, on the works of those who have laboured in this
field -- a glance which reveals [many stately] structures, but in
ruins only. 
It is a very notable fact, although it could not have been
otherwise, that in the infancy of philosophy men began where
we should incline to end, namely, with the knowledge of God,
occupying themselves with the hope, or rather indeed with
the specific nature, of another world. However gross the
religious concepts generated by the ancient practices which
still persisted in each community from an earlier more
barbarous state, this did not prevent the more enlightened
members from devoting themselves to free investigation of
these matters; and they easily discerned that there could be
no better ground or more dependable way of pleasing the in-
visible power that governs the world, and so of being happy
in another world at least, than by living the good life. Ac-
cordingly theology and morals were the two motives, or rather
the two points of reference, in all those abstract enquiries of
reason to which men came to devote themselves. It was chiefly,
however, the former that step by step committed the purely
speculative reason to those labours which afterwards became
so renowned under the name of metaphysics. 
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I shall not here attempt to distinguish the periods of his-
tory in which this or that change in metaphysics came about,
but shall only give a cursory sketch of the various ideas which
gave rise to the chief revolutions [in metaphysical theory]. 
And here I find that there are three issues in regard to
which the most noteworthy changes have taken place in the
course of the resulting controversies. 
1. In respect of the object of all our 'knowledge through
reason', some have been mere sensualists, others mere intel-
lectualists. Epicurus may be regarded as the outstanding
philosopher among the former, and Plato among the latter. 
The distinction between the two schools, subtle as it is,
dates from the earliest times; and the two positions have
ever since been maintained in unbroken continuity. Those
of the former school maintained that reality is to be found
solely in the objects of the senses, and that all else is fiction;
those of the latter school, on the other hand, declared that
in the senses there is nothing but illusion, and that only
the understanding knows what is true. The former did not
indeed deny reality to the concepts of the understanding; but
this reality was for them merely logical, whereas for the others
it was mystical. The former conceded intellectual concepts, but
admitted sensible objects only. The latter required that true
objects should be purely intelligible, and maintained that by
means of the pure understanding we have an intuition that
is unaccompanied by the senses -- the senses, in their view,
serving only to confuse the understanding. 
2. In respect of the origin of the modes of 'knowledge
through pure reason', the question is as to whether they are
derived from experience, or whether in independence of ex-
perience they have their origin in reason. Aristotle may be
regarded as the chief of the empiricists, and Plato as the
chief of the noologists. Locke, who in modern times followed
Aristotle, and Leibniz, who followed Plato (although in con-
siderable disagreement with his mystical system), have not
been able to bring this conflict to any definitive conclusion. 
However we may regard Epicurus, he was at least much more
consistent in this sensual system than Aristotle and Locke,
inasmuch as he never sought to pass by inference beyond the
limits of experience. This is especially true as regards Locke,
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who, after having derived all concepts and principles from
experience, goes so far in the use of them as to assert that we
can prove the existence of God and the immortality of the
soul with the same conclusiveness as any mathematical pro-
position -- though both lie entirely outside the limits of
possible experience. 
3. In respect of method. -- If anything is to receive the
title of method, it must be a procedure in accordance with
principles. We may divide the methods now prevailing in this
field of enquiry into the naturalistic and the scientific. The
naturalist of pure reason adopts as his principle that through
common reason, without science, that is, through what he
calls sound reason, he is able, in regard to those most sublime
questions which form the problem of metaphysics, to achieve
more than is possible through speculation. Thus he is virtu-
ally asserting that we can determine the size and distance of
the moon with greater certainty by the naked eye than by
mathematical devices. This is mere misology, reduced to
principles; and what is most absurd of all, the neglect of all
artificial means is eulogised as a special method of extending
our knowledge. For as regards those who are naturalists from
lack of more insight, they cannot rightly be blamed. They
follow common reason, without boasting of their ignorance
as a method which contains the secret how we are to fetch
truth from the deep well of Democritus. Quod sapio, satis
est mihi, non ego curo, esse quod Arcesilas aerumnosique
Solones is the motto with which they may lead a cheerful
and praiseworthy life, not troubling themselves about science,
nor by their interference bringing it into confusion. 
As regards those who adopt a scientific method, they have
the choice of proceeding either dogmatically or sceptically;
but in any case they are under obligation to proceed system-
atically. I may cite the celebrated Wolff as a representative
of the former mode of procedure, and David Hume as a repre-
sentative of the latter, and may then, conformably with my
present purpose, leave all others unnamed. The critical path
alone is still open. If the reader has had the courtesy and
patience to accompany me along this path, he may now judge
for himself whether, if he cares to lend his aid in making this
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path into a high-road, it may not be possible to achieve be-
fore the end of the present century what many centuries have
not been able to accomplish; namely, to secure for human
reason complete satisfaction in regard to that with which it
has all along so eagerly occupied itself, though hitherto
in vain. 
P 668n
++ Persius.