Critique of Pure Reason


P 063
P 065
IN whatever manner and by whatever means a mode of know-
ledge may relate to objects, intuition is that through which it
is in immediate relation to them, and to which all thought as a
means is directed. But intuition takes place only in so far as the
object is given to us. This again is only possible, to man at least,
in so far as the mind is affected in a certain way. The capacity
(receptivity) for receiving representations through the mode
in which we are affected by objects, is entitled sensibility. 
Objects are given to us by means of sensibility, and it alone
yields us intuitions; they are thought through the understand-
ing, and from the understanding arise concepts. But all thought
must, directly or indirectly, by way of certain characters
relate ultimately to intuitions, and therefore, with us, to sensi-
bility, because in no other way can an object be given to us. 
The effect of an object upon the faculty of representation,
so far as we are affected by it, is sensation. That intuition
which is in relation to the object through sensation, is entitled
empirical. The undetermined object of an empirical intuition
is entitled appearance. 
That in the appearance which corresponds to sensation
P 066
I term its matter; but that which so determines the manifold
of appearance that it allows of being ordered in certain re-
lations, I term the form of appearance. That in which alone
the sensations can be posited and ordered in a certain form,
cannot itself be sensation; and therefore, while the matter of
all appearance is given to us a posteriori only, its form must
lie ready for the sensations a priori in the mind, and so must
allow of being considered apart from all sensation. 
I term all representations pure (in the transcendental
sense) in which there is nothing that belongs to sensation. The
pure form of sensible intuitions in general, in which all the
manifold of intuition is intuited in certain relations, must be
found in the mind a priori. This pure form of sensibility may
also itself be called pure intuition. Thus, if I take away from
the representation of a body that which the understanding
thinks in regard to it, substance, force, divisibility, etc. , and
likewise what belongs to sensation, impenetrability, hardness,
colour, etc. , something still remains over from this empirical
intuition, namely, extension and figure. These belong to pure
intuition, which, even without any actual object of the senses
or of sensation, exists in the mind a priori as a mere form
of sensibility. 
The science of all principles of a priori sensibility I call
transcendental aesthetic. 
 The Germans are the only people who currently make use of
the word 'aesthetic' in order to signify what others call the critique
of taste. This usage originated in the abortive attempt made by
Baumgarten, that admirable analytical thinker, to bring the critical
treatment of the beautiful under rational principles, and so to raise its
rules to the rank of a science. But such endeavours are fruitless. 
The said rules or criteria are, as regards their chief sources, merely
empirical, and consequently can never serve as determinate a -
priori laws by which our judgment of taste must be directed. On
the contrary, our judgment is the proper test of the correctness
of the rules. For this reason it is advisable either to give up
using the name in this sense of critique of taste, and to reserve
it for that doctrine of sensibility which is true science -- thus
P 067n
approximating to the language and sense of the ancients, in their
far-famed division of knowledge into aisthyta kai noyta -- or else
to share the name with speculative philosophy, employing it partly
in the transcendental and partly in the psychological sense. 
P 066
There must be such a science, forming
P 067
the first part of the transcendental doctrine of elements,
in distinction from that part which deals with the principles
of pure thought, and which is called transcendental logic. 
In the transcendental aesthetic we shall, therefore, first
isolate sensibility, by taking away from it everything which the
understanding thinks through its concepts, so that nothing
may be left save empirical intuition. Secondly, we shall also
separate off from it everything which belongs to sensation, so
that nothing may remain save pure intuition and the mere
form of appearances, which is all that sensibility can supply
a priori. In the course of this investigation it will be found
that there are two pure forms of sensible intuition, serving as
principles of a priori knowledge, namely, space and time. To
the consideration of these we shall now proceed. 
Metaphysical Exposition of this Concept 
By means of outer sense, a property of our mind, we repre-
sent to ourselves objects as outside us, and all without excep-
tion in space. In space their shape, magnitude, and relation to
one another are determined or determinable. Inner sense,
by means of which the mind intuits itself or its inner state,
yields indeed no intuition of the soul itself as an object; but
there is nevertheless a determinate form [namely, time] in
which alone the intuition of inner states is possible, and every-
thing which belongs to inner determinations is therefore
P 068
represented in relations of time. Time cannot be outwardly
intuited, any more than space can be intuited as something
in us. What, then, are space and time? Are they real exist-
ences? Are they only determinations or relations of things, yet
such as would belong to things even if they were not intuited? 
Or are space and time such that they belong only to the form
of intuition, and therefore to the subjective constitution of our
mind, apart from which they could not be ascribed to anything
whatsoever? In order to obtain light upon these questions,
let us first give an exposition of the concept of space. By
exposition (expositio) I mean the clear, though not necessarily
exhaustive, representation of that which belongs to a concept:
the exposition is metaphysical when it contains that which
exhibits the concept as given a priori. 
1. Space is not an empirical concept which has been de-
rived from outer experiences. For in order that certain sensa-
tions be referred to something outside me (that is, to something
in another region of space from that in which I find myself),
and similarly in order that I may be able to represent them as
outside and alongside one another, and accordingly as not
only different but as in different places, the representation of
space must be presupposed. The representation of space can-
not, therefore, be empirically obtained from the relations of
outer appearance. On the contrary, this outer experience is
itself possible at all only through that representation. 
 2. Space is a necessary a priori representation, which
underlies all outer intuitions. We can never represent to our-
selves the absence of space, though we can quite well think it
as empty of objects. It must therefore be regarded as the con-
dition of the possibility of appearances, and not as a determina-
tion dependent upon them. It is an a priori representation,
which necessarily underlies outer appearances. 
* 3. The apodeictic certainty of all geometrical propositions
and the possibility of their a priori construction is grounded
in this a priori necessity of space. 
P 069
3. Space is not a discursive or, as we say, general concept
of relations of things in general, but a pure intuition. For, in the
first place, we can represent to ourselves only one space; and
if we speak of diverse spaces, we mean thereby only parts of
one and the same unique space. Secondly, these parts cannot
precede the one all-embracing space, as being, as it were,
constituents out of which it can be composed; on the contrary,
they can be thought only as in it. Space is essentially one;
the manifold in it, and therefore the general concept of spaces,
depends solely on [the introduction of] limitations. Hence it
follows that an a priori, and not an empirical, intuition under-
lies all concepts of space. For kindred reasons, geometrical
propositions, that, for instance, in a triangle two sides
together are greater than the third, can never be derived
from the general concepts of line and triangle, but only
from intuition, and this indeed a priori, with apodeictic
4. Space is represented as an infinite given magnitude. 
P 068a
Were this representation of
P 069a
space a concept acquired a posteriori, and derived from outer
experience in general, the first principles of mathematical
determination would be nothing but perceptions. They would
therefore all share in the contingent character of perception;
that there should be only one straight line between two points
would not be necessary, but only what experience always
teaches. What is derived from experience has only compara-
tive universality, namely, that which is obtained through in-
duction. We should therefore only be able to say that, so far
as hitherto observed, no space has been found which has more
than three dimensions. 
 * 5. Space is represented as an infinite given magnitude. 
A general concept of space, which is found alike in a foot and
in an ell, cannot determine anything in regard to magnitude. 
If there were no limitlessness in the progression of intuition,
no concept of relations could yield a principle of their infini-
P 069
Now every concept must be thought as a representation
which is contained in an infinite number of different possible
P 070
representations (as their common character), and which
therefore contains these under itself; but no concept, as such,
can be thought as containing an infinite number of representa-
tions within itself. It is in this latter way, however, that space
is thought; for all the parts of space coexist ad infinitum. 
Consequently, the original representation of space is an a -
priori intuition, not a concept. 
The Transcendental Exposition of the Concept of Space 
I understand by a transcendental exposition the explana-
tion of a concept, as a principle from which the possibility
of other a priori synthetic knowledge can be understood. 
For this purpose it is required (1) that such knowledge does
really flow from the given concept, (2) that this knowledge is
possible only on the assumption of a given mode of explaining
the concept. 
Geometry is a science which determines the properties
of space synthetically, and yet a priori. What, then, must be
our representation of space, in order that such knowledge
of it may be possible? It must in its origin be intuition; for
from a mere concept no propositions can be obtained which
go beyond the concept -- as happens in geometry (Introduc-
tion, V). Further, this intuition must be a priori, that is,
it must be found in us prior to any perception of an object,
and must therefore be pure, not empirical, intuition. For
geometrical propositions are one and all apodeictic, that is,
are bound up with the consciousness of their necessity; for
instance, that space has only three dimensions. Such pro-
positions cannot be empirical or, in other words, judgments
of experience, nor can they be derived from any such judg-
ments (Introduction, II). 
How, then, can there exist in the mind an outer intui-
tion which precedes the objects themselves, and in which
the concept of these objects can be determined a priori? 
Manifestly, not otherwise than in so far as the intuition has
its seat in the subject only, as the formal character of the
P 071
subject, in virtue of which, in being affected by objects, it
obtains immediate representation, that is, intuition, of them;
and only in so far, therefore, as it is merely the form of outer
sense in general. 
Our explanation is thus the only explanation that makes
intelligible the possibility of geometry, as a body of a priori
synthetic knowledge. Any mode of explanation which fails to
do this, although it may otherwise seem to be somewhat
similar, can by this criterion be distinguished from it with
the greatest certainty. 
Conclusions from the above Concepts 
(a) Space does not represent any property of things in
themselves, nor does it represent them in their relation to
one another. That is to say, space does not represent any
determination that attaches to the objects themselves, and
which remains even when abstraction has been made of all
the subjective conditions of intuition. For no determina-
tions, whether absolute or relative, can be intuited prior to
the existence of the things to which they belong, and none,
therefore, can be intuited a priori. 
(b) Space is nothing but the form of all appearances
of outer sense. It is the subjective condition of sensibility,
under which alone outer intuition is possible for us. Since,
then, the receptivity of the subject, its capacity to be affected
by objects, must necessarily precede all intuitions of these
objects, it can readily be understood how the form of all
appearances can be given prior to all actual perceptions, and
so exist in the mind a priori, and how, as a pure intuition, in
which all objects must be determined, it can contain, prior
to all experience, principles which determine the relations
of these objects. 
It is, therefore, solely from the human standpoint that
we can speak of space, of extended things, etc. If we depart
from the subjective condition under which alone we can have
outer intuition, namely, liability to be affected by objects,
the representation of space stands for nothing whatsoever. 
P 072
 This predicate can be ascribed to things only in so far as they
appear to us, that is, only to objects of sensibility. The con-
stant form of this receptivity, which we term sensibility, is a
necessary condition of all the relations in which objects can
be intuited as outside us; and if we abstract from these
objects, it is a pure intuition, and bears the name of space. 
Since we cannot treat the special conditions of sensibility as
conditions of the possibility of things, but only of their appear-
ances, we can indeed say that space comprehends all things
that appear to us as external, but not all things in themselves,
by whatever subject they are intuited, or whether they be
intuited or not. For we cannot judge in regard to the intui-
tions of other thinking beings, whether they are bound by
the same conditions as those which limit our intuition and
which for us are universally valid. If we add to the concept of
the subject of a judgment the limitation under which the judg-
ment is made, the judgment is then unconditionally valid. 
The proposition, that all things are side by side in space, is
valid under the limitation that these things are viewed as
objects of our sensible intuition. If, now, I add the condition
to the concept, and say that all things, as outer appearances,
are side by side in space, the rule is valid universally and
without limitation. Our exposition therefore establishes the
reality, that is, the objective validity, of space in respect of
whatever can be presented to us outwardly as object, but also
at the same time the ideality of space in respect of things when
they are considered in themselves through reason, that is,
without regard to the constitution of our sensibility. We
assert, then, the empirical reality of space, as regards all
possible outer experience; and yet at the same time we
assert its transcendental ideality -- in other words, that it
is nothing at all, immediately we withdraw the above con-
dition, namely, its limitation to possible experience, and so
look upon it as something that underlies things in them-
With the sole exception of space there is no subjective
representation, referring to something outer, which could be
P 073
entitled [at once] objective [and] a priori. For there is no other
subjective representation from which we can derive a priori
synthetic propositions, as we can from intuition in space ($3). 
Strictly speaking, therefore, these other representations have no
ideality, although they agree with the representation of space in
this respect, that they belong merely to the subjective constitu-
tion of our manner of sensibility, for instance, of sight, hearing,
touch, as in the case of the sensations of colours, sounds, and
heat, which, since they are mere sensations and not intuitions,
do not of themselves yield knowledge of any object, least of
all any a priori knowledge. 
The above remark is intended only to guard anyone from
supposing that the ideality of space as here asserted can be
illustrated by examples so altogether insufficient as colours,
taste, etc. For these cannot rightly be regarded as properties
of things, but only as changes in the subject, changes which
may, indeed, be different for different men. In such examples
as these, that which originally is itself only appearance, for
instance, a rose, is being treated by the empirical understand-
ing as a thing in itself, which, nevertheless, in respect of its
colour, can appear differently to every observer. 
* This subjective condition of all outer appearances cannot,
therefore, be compared to any other. The taste of a wine does
not belong to the objective determinations of the wine, not
even if by the wine as an object we mean the wine as appear-
ance, but to the special constitution of sense in the subject that
tastes it. Colours are not properties of the bodies to the in-
tuition of which they are attached, but only modifications of
the sense of sight, which is affected in a certain manner by
light. Space, on the other hand, as condition of outer objects,
necessarily belongs to their appearance or intuition. Taste and
colours are not necessary conditions under which alone objects
can be for us objects of the senses. 
P 073
The tran-
scendental concept of appearances in space, on the other hand,
is a critical reminder that nothing intuited in space is a thing
in itself, that space is not a form inhering in things in themselves
P 074
as their intrinsic property, that objects in themselves are
quite unknown to us, and that what we call outer objects are
nothing but mere representations of our sensibility, the form
of which is space. The true correlate of sensibility, the thing
in itself, is not known, and cannot be known, through these
representations; and in experience no question is ever asked
in regard to it. 
Metaphysical exposition of the Concept of Time 
1. Time is not an empirical concept that has been
derived from any experience. For neither coexistence nor
succession would ever come within our perception, if the repre-
sentation of time were not presupposed as underlying them
a priori. Only on the presupposition of time can we represent
to ourselves a number of things as existing at one and the
same time (simultaneously) or at different times (successively). 
P 073a
They are connected with
P 074a
the appearances only as effects accidentally added by the par-
ticular constitution of the sense organs. Accordingly, they are
not a priori representations, but are grounded in sensation,
and, indeed, in the case of taste, even upon feeling (pleasure
and pain), as an effect of sensation. Further, no one can have
a priori a representation of a colour or of any taste; whereas,
since space concerns only the pure form of intuition, and
therefore involves no sensation whatsoever, and nothing em-
pirical, all kinds and determinations of space can and must be
represented a priori, if concepts of figures and of their rela-
tions are to arise. Through space alone is it possible that
things should be outer objects to us. 
P 074
2. Time is a necessary representation that underlies all
P 075
intuitions. We cannot, in respect of appearances in general,
remove time itself, though we can quite well think time as void
of appearances. Time is, therefore, given a priori. In it alone
is actuality of appearances possible at all. Appearances may,
one and all, vanish; but time (as the universal condition of
their possibility) cannot itself be removed. 
3. The possibility of apodeictic principles concerning the
relations of time, or of axioms of time in general, is also
grounded upon this a priori necessity. Time has only one
dimension; different times are not simultaneous but successive
(just as different spaces are not successive but simultaneous). 
These principles cannot be derived from experience, for ex-
perience would give neither strict universality nor apodeictic
certainty. We should only be able to say that common experi-
ence teaches us that it is so; not that it must be so. These
principles are valid as rules under which alone experiences are
possible; and they instruct us in regard to the experiences,
not by means of them. 
4. Time is not a discursive, or what is called a general con-
cept, but a pure form of sensible intuition. Different times are
but parts of one and the same time; and the representation
which can be given only through a single object is intuition. 
Moreover, the proposition that different times cannot be
simultaneous is not to be derived from a general concept. 
The proposition is synthetic, and cannot have its origin in
concepts alone. It is immediately contained in the intuition
and representation of time. 
5. The infinitude of time signifies nothing more than that
every determinate magnitude of time is possible only through
limitations of one single time that underlies it. The original
representation, time, must therefore be given as unlimited. 
But when an object is so given that its parts, and every quan-
tity of it, can be determinately represented only through
limitation, the whole representation cannot be given through
concepts, since they contain only partial representations; on
the contrary, such concepts must themselves rest on immediate
P 076
The Transcendental exposition of the Concept of Time 
I may here refer to No. 3, where, for the sake of brevity,
I have placed under the title of metaphysical exposition what
is properly transcendental. Here I may add that the concept
of alteration, and with it the concept of motion, as alteration
of place, is possible only through and in the representation
of time; and that if this representation were not an a priori
(inner) intuition, no concept, no matter what it might be, could
render comprehensible the possibility of an alteration, that is,
of a combination of contradictorily opposed predicates in one
and the same object, for instance, the being and the not-being
of one and the same thing in one and the same place. Only in
time can two contradictorily opposed predicates meet in one
and the same object, namely, one after the other. Thus our
concept of time explains the possibility of that body of a priori
synthetic knowledge which is exhibited in the general doc-
trine of motion, and which is by no means unfruitful. 
Conclusions from these Concepts 
(a) Time is not something which exists of itself, or which
inheres in things as an objective determination, and it does
not, therefore, remain when abstraction is made of all sub-
jective conditions of its intuition. Were it self-subsistent, it
would be something which would be actual and yet not an
actual object. Were it a determination or order inhering in
things themselves, it could not precede the objects as their
condition, and be known and intuited a priori by means of
synthetic propositions. But this last is quite possible if time
is nothing but the subjective condition under which alone
intuition can take place in us. For that being so, this form
of inner intuition can be represented prior to the objects, and
therefore a priori. 
P 077
(b) Time is nothing but the form of inner sense, that is, of
the intuition of ourselves and of our inner state. It cannot be a
determination of outer appearances; it has to do neither with
shape nor position, but with the relation of representations in
our inner state. And just because this inner intuition yields no
shape, we endeavour to make up for this want by analogies. 
We represent the time-sequence by a line progressing to in-
finity, in which the manifold constitutes a series of one dimen-
sion only; and we reason from the properties of this line to all
the properties of time, with this one exception, that while the
parts of the line are simultaneous the parts of time are always
successive. From this fact also, that all the relations of time
allow of being expressed in an outer intuition, it is evident that
the representation is itself an intuition. 
(c) Time is the formal a priori condition of all appearances
whatsoever. Space, as the pure form of all outer intuition, is so
far limited; it serves as the a priori condition only of outer
appearances. But since all representations, whether they have
for their objects outer things or not, belong, in themselves, as
determinations of the mind, to our inner state; and since this
inner state stands under the formal condition of inner intui-
tion, and so belongs to time, time is an a priori condition of
all appearance whatsoever. It is the immediate condition of
inner appearances (of our souls), and thereby the mediate con-
dition of outer appearances. Just as I can say a priori that
all outer appearances are in space, and are determined a priori
in conformity with the relations of space, I can also say, from
the principle of inner sense, that all appearances whatsoever,
that is, all objects of the senses, are in time, and necessarily
stand in time-relations. 
If we abstract from our mode of inwardly intuiting our-
selves -- the mode of intuition in terms of which we likewise
take up into our faculty of representation all outer intuitions --
and so take objects as they may be in themselves, then time is
nothing. It has objective validity only in respect of appear-
ances, these being things which we take as objects of our
senses. It is no longer objective, if we abstract from the sensi-
bility of our intuition, that is, from that mode of representation
which is peculiar to us, and speak of things in general. Time is
P 078
therefore a purely subjective condition of our (human) intuition
(which is always sensible, that is, so far as we are affected by
objects), and in itself, apart from the subject, is nothing. 
Nevertheless, in respect of all appearances, and therefore of
all the things which can enter into our experience, it is neces-
sarily objective. We cannot say that all things are in time, be-
cause in this concept of things in general we are abstracting
from every mode of their intuition and therefore from that
condition under which alone objects can be represented as
being in time. If, however, the condition be added to the
concept, and we say that all things as appearances, that is, as
objects of sensible intuition, are in time, then the proposition
has legitimate objective validity and universality a priori. 
What we are maintaining is, therefore, the empirical
reality of time, that is, its objective validity in respect of all
objects which allow of ever being given to our senses. And
since our intuition is always sensible, no object can ever be
given to us in experience which does not conform to the
condition of time. On the other hand, we deny to time all
claim to absolute reality; that is to say, we deny that it belongs
to things absolutely, as their condition or property, independ-
ently of any reference to the form of our sensible intuition;
properties that belong to things in themselves can never be
given to us through the senses. This, then, is what constitutes
the transcendental ideality of time. What we mean by this
phrase is that if we abstract from the subjective conditions of
sensible intuition, time is nothing, and cannot be ascribed to
the objects in themselves (apart from their relation to our in-
tuition) in the way either of subsistence or of inherence. This
ideality, like that of space, must not, however, be illustrated
by false analogies with sensation, because it is then assumed
that the appearance, in which the sensible predicates inhere,
itself has objective reality. In the case of time, such objective
reality falls entirely away, save in so far as it is merely empir-
ical, that is, save in so far as we regard the object itself merely
as appearance. On this subject, the reader may refer to what
has been said at the close of the preceding section. 
P 079
Against this theory, which admits the empirical reality of
time, but denies its absolute and transcendental reality, I have
heard men of intelligence so unanimously voicing an objection,
that I must suppose it to occur spontaneously to every reader
to whom this way of thinking is unfamiliar. The objection is
this. Alterations are real, this being proved by change of our
own representations -- even if all outer appearances, together
with their alterations, be denied. Now alterations are possible
only in time, and time is therefore something real. There is no
difficulty in meeting this objection. I grant the whole argument. 
Certainly time is something real, namely, the real form of inner
intuition. It has therefore subjective reality in respect of inner
experience; that is, I really have the representation of time and
of my determinations in it. Time is therefore to be regarded
as real, not indeed as object but as the mode of representation
of myself as object. If without this condition of sensibility I
could intuit myself, or be intuited by another being, the very
same determinations which we now represent to ourselves as
alterations would yield knowledge into which the representa-
tion of time, and therefore also of alteration, would in no
way enter. Thus empirical reality has to be allowed to time, as
the condition of all our experiences; on our theory, it is only
its absolute reality that has to be denied. It is nothing but the
form of our inner intuition. If we take away from our inner
intuition the peculiar condition of our sensibility, the concept
of time likewise vanishes; it does not inhere in the objects, but
merely in the subject which intuits them. 
 I can indeed say that my representations follow one another;
but this is only to say that we are conscious of them as in a time-
sequence, that is, in conformity with the form of inner sense. Time
is not, therefore, something in itself, nor is it an objective determina-
tion inherent in things. 
P 079
But the reason why this objection is so unanimously urged,
P 080
and that too by those who have nothing very convincing to say
against the doctrine of the ideality of space, is this. They have
no expectation of being able to prove apodeictically the abso-
lute reality of space; for they are confronted by idealism,
which teaches that the reality of outer objects does not allow
of strict proof. On the other hand, the reality of the object of
our inner sense (the reality of myself and my state) is, [they
argue,] immediately evident through consciousness. The
former may be merely an illusion; the latter is, on their view,
undeniably something real. What they have failed, how-
ever, to recognise is that both are in the same position; in
neither case can their reality as representations be questioned,
and in both cases they belong only to appearance, which
always has two sides, the one by which the object is viewed in
and by itself (without regard to the mode of intuiting it -- its
nature therefore remaining always problematic), the other
by which the form of the intuition of this object is taken into
account. This form is not to be looked for in the object in it-
self, but in the subject to which the object appears; neverthe-
less, it belongs really and necessarily to the appearance of this
Time and space are, therefore, two sources of knowledge,
from which bodies of a priori synthetic knowledge can be
derived. (Pure mathematics is a brilliant example of such
knowledge, especially as regards space and its relations. )
Time and space, taken together, are the pure forms of all
sensible intuition, and so are what make a priori synthetic
propositions possible. But these a priori sources of know-
ledge, being merely conditions of our sensibility, just by
this very fact determine their own limits, namely, that they
apply to objects only in so far as objects are viewed as appear-
ances, and do not present things as they are in themselves. This
is the sole field of their validity; should we pass beyond it, no
objective use can be made of them. This ideality of space
and time leaves, however, the certainty of empirical know-
ledge unaffected, for we are equally sure of it, whether these
forms necessarily inhere in things in themselves or only
in our intuition of them. Those, on the other hand, who
maintain the absolute reality of space and time, whether as
P 081
subsistent or only as inherent, must come into conflict with
the principles of experience itself. For if they decide for the
former alternative (which is generally the view taken by
mathematical students of nature), they have to admit two
eternal and infinite self-subsistent non-entities (space and
time), which are there (yet without there being anything real)
only in order to contain in themselves all that is real. If they
adopt the latter alternative (as advocated by certain meta-
physical students of nature), and regard space and time as
relations of appearances, alongside or in succession to one
another -- relations abstracted from experience, and in this
isolation confusedly represented -- they are obliged to deny
that a priori mathematical doctrines have any validity in
respect of real things (for instance, in space), or at least to
deny their apodeictic certainty. For such certainty is not to
be found in the a posteriori. On this view, indeed, the a priori
concepts of space and time are merely creatures of the im-
agination, whose source must really be sought in experience,
the imagination framing out of the relations abstracted from
experience something that does indeed contain what is
general in these relations, but which cannot exist without
the restrictions which nature has attached to them. The
former thinkers obtain at least this advantage, that they keep
the field of appearances open for mathematical propositions. 
On the other hand, they have greatly embarrassed them-
selves by those very conditions [space and time, eternal,
infinite, and self-subsistent], when with the understanding
they endeavour to go out beyond this field. The latter have
indeed an advantage, in that the representations of space
and time do not stand in their way if they seek to judge
of objects, not as appearances but merely in their relation
to the understanding. But since they are unable to appeal to
a true and objectively valid a priori intuition, they can neither
account for the possibility of a priori mathematical know-
ledge, nor bring the propositions of experience into necessary
agreement with it. On our theory of the true character of
these two original forms of sensibility, both difficulties are
Lastly, transcendental aesthetic cannot contain more than
P 082
these two elements, space and time. This is evident from the
fact that all other concepts belonging to sensibility, even
that of motion, in which both elements are united, presuppose
something empirical. Motion presupposes the perception of
something movable. But in space, considered in itself, there
is nothing movable; consequently the movable must be
something that is found in space only through experience,
and must therefore be an empirical datum. For the same
reason, transcendental aesthetic cannot count the concept
of alteration among its a priori data. Time itself does not
alter, but only something which is in time. The concept of
time thus presupposes the perception of something existing
and of the succession of its determinations; that is to say, it
presupposes experience. 
General Observations on Transcendental Aesthetic 
I. To avoid all misapprehension, it is necessary to ex-
plain, as clearly as possible, what our view is regarding the
fundamental constitution of sensible knowledge in general. 
What we have meant to say is that all our intuition is
nothing but the representation of appearance; that the things
which we intuit are not in themselves what we intuit them
as being, nor their relations so constituted in themselves as
they appear to us, and that if the subject, or even only the
subjective constitution of the senses in general, be removed,
the whole constitution and all the relations of objects in
space and time, nay space and time themselves, would vanish. 
As appearances, they cannot exist in themselves, but only
in us. What objects may be in themselves, and apart from
all this receptivity of our sensibility, remains completely
unknown to us. We know nothing but our mode of perceiving
them -- a mode which is peculiar to us, and not necessarily
shared in by every being, though, certainly, by every human
being. With this alone have we any concern. Space and time
are its pure forms, and sensation in general its matter. The
former alone can we know a priori, that is, prior to all actual
perception; and such knowledge is therefore called pure
P 083
intuition. The latter is that in our knowledge which leads to
its being called a posteriori knowledge, that is, empirical
intuition. The former inhere in our sensibility with absolute
necessity, no matter of what kind our sensations may be; the
latter can exist in varying modes. Even if we could bring our
intuition to the highest degree of clearness, we should not
thereby come any nearer to the constitution of objects in
themselves. We should still know only our mode of intuition,
that is, our sensibility. We should, indeed, know it completely,
but always only under the conditions of space and time --
conditions which are originally inherent in the subject. 
What the objects may be in themselves would never be-
come known to us even through the most enlightened
knowledge of that which is alone given us, namely, their
The concept of sensibility and of appearance would be
falsified, and our whole teaching in regard to them would be
rendered empty and useless, if we were to accept the view that
our entire sensibility is nothing but a confused representation
of things, containing only what belongs to them in themselves,
but doing so under an aggregation of characters and partial
representations that we do not consciously distinguish. For
the difference between a confused and a clear representation
is merely logical, and does not concern the content. No doubt
the concept of 'right', in its common-sense usage, contains all
that the subtlest speculation can develop out of it, though in
its ordinary and practical use we are not conscious of the
manifold representations comprised in this thought But we
cannot say that the common concept is therefore sensible, con-
taining a mere appearance. For 'right' can never be an appear-
ance; it is a concept in the understanding, and represents a
property (the moral property) of actions, which belongs to
them in themselves. The representation of a body in intuition,
on the other hand, contains nothing that can belong to an
object in itself, but merely the appearance of something, and
the mode in which we are affected by that something; and this
receptivity of our faculty of knowledge is termed sensibility. 
Even if that appearance could become completely transparent
P 084
to us, such knowledge would remain toto coelo different from
knowledge of the object in itself. 
The philosophy of Leibniz and Wolff, in thus treating the
difference between the sensible and the intelligible as merely
logical, has given a completely wrong direction to all in-
vestigations into the nature and origin of our knowledge. This
difference is quite evidently transcendental. It does not merely
concern their [logical] form, as being either clear or confused. 
It concerns their origin and content. It is not that by our
sensibility we cannot know the nature of things in themselves
in any save a confused fashion; we do not apprehend them in
any fashion whatsoever. If our subjective constitution be re-
moved, the represented object, with the qualities which sen-
sible intuition bestows upon it, is nowhere to be found, and
cannot possibly be found. For it is this subjective constitution
which determines its form as appearance. 
 We commonly distinguish in appearances that which is
essentially inherent in their intuition and holds for sense in all
human beings, from that which belongs to their intuition
accidentally only, and is valid not in relation to sensibility in
general but only in relation to a particular standpoint or to a
peculiarity of structure in this or that sense. The former kind
of knowledge is then declared to represent the object in itself,
the latter its appearance only. But this distinction is merely
empirical. If, as generally happens, we stop short at this point,
and do not proceed, as we ought, to treat the empirical in-
tuition as itself mere appearance, in which nothing that belongs
to a thing in itself can be found, our transcendental distinction
is lost. We then believe that we know things in themselves,
and this in spite of the fact that in the world of sense, how-
ever deeply we enquire into its objects, we have to do with
nothing but appearances. The rainbow in a sunny shower may
be called a mere appearance, and the rain the thing in itself. 
This is correct, if the latter concept be taken in a merely
physical sense. Rain will then be viewed only as that which,
in all experience and in all its various positions relative to the
senses, is determined thus, and not otherwise, in our intuition. 
But if we take this empirical object in its general character,
and ask, without considering whether or not it is the same
for all human sense, whether it represents an object in
P 085
itself (and by that we cannot mean the drops of rain, for these
are already, as appearances, empirical objects), the question
as to the relation of the representation to the object at once
becomes transcendental. We then realise that not only are the
drops of rain mere appearances, but that even their round
shape, nay even the space in which they fall, are nothing in
themselves, but merely modifications or fundamental forms of
our sensible intuition, and that the transcendental object
remains unknown to us. 
The second important concern of our Transcendental Aes-
thetic is that it should not obtain favour merely as a plausible
hypothesis, but should have that certainty and freedom from
doubt which is required of any theory that is to serve as an
organon. To make this certainty completely convincing, we
shall select a case by which the validity of the position adopted
will be rendered obvious, and which will serve to set what has
been said in $3 in a clearer light. 
Let us suppose that space and time are in themselves
objective, and are conditions of the possibility of things in
themselves. In the first place, it is evident that in regard to
both there is a large number of a priori apodeictic and syn-
thetic propositions. This is especially true of space, to which
our chief attention will therefore be directed in this enquiry. 
Since the propositions of geometry are synthetic a priori, and
are known with apodeictic certainty, I raise the question,
whence do you obtain such propositions, and upon what does
the understanding rely in its endeavour to achieve such abso-
lutely necessary and universally valid truths? There is no
other way than through concepts or through intuitions; and
these are given either a priori or a posteriori. In their latter
form, namely, as empirical concepts, and also as that upon
which these are grounded, the empirical intuition, neither the
concepts nor the intuitions can yield any synthetic proposition
except such as is itself also merely empirical (that is, a pro-
position of experience), and which for that very reason can
never possess the necessity and absolute universality which are
characteristic of all geometrical propositions. As regards the
first and sole means of arriving at such knowledge, namely,
in a priori fashion through mere concepts or through in-
tuitions, it is evident that from mere concepts only analytic
P 086
knowledge, not synthetic knowledge, is to be obtained. Take,
for instance, the proposition, "Two straight lines cannot en-
close a space, and with them alone no figure is possible",
and try to derive it from the concept of straight lines and of
the number two. Or take the proposition, "Given three straight
lines, a figure is possible", and try, in like manner, to derive
it from the concepts involved. All your labour is vain; and you
find that you are constrained to have recourse to intuition, as is
always done in geometry. You therefore give yourself an object
in intuition. But of what kind is this intuition? Is it a pure a -
priori intuition or an empirical intuition? Were it the latter,
no universally valid proposition could ever arise out of it --
still less an apodeictic proposition -- for experience can never
yield such. You must therefore give yourself an object a priori
in intuition, and ground upon this your synthetic proposition. 
If there did not exist in you a power of a priori intuition; and
if that subjective condition were not also at the same time, as
regards its form, the universal a priori condition under which
alone the object of this outer intuition is itself possible; if the
object (the triangle) were something in itself, apart from any
relation to you, the subject, how could you say that what
necessarily exist in you as subjective conditions for the con-
struction of a triangle, must of necessity belong to the triangle
itself? You could not then add anything new (the figure) to
your concepts (of three lines) as something which must neces-
sarily be met with in the object, since this object is [on that
view] given antecedently to your knowledge, and not by means
of it. If, therefore, space (and the same is true of time) were
not merely a form of your intuition, containing conditions a -
priori, under which alone things can be outer objects to you,
and without which subjective conditions outer objects are in
themselves nothing, you could not in regard to outer objects
determine anything whatsoever in an a priori and synthetic
manner. It is, therefore, not merely possible or probable, but
indubitably certain, that space and time, as the necessary
conditions of all outer and inner experience, are merely sub-
jective conditions of all our intuition, and that in relation to
these conditions all objects are therefore mere appearances,
and not given us as things in themselves which exist in this
P 087
manner. For this reason also, while much can be said a priori
as regards the form of appearances, nothing whatsoever can
be asserted of the thing in itself, which may underlie these
II. In confirmation of this theory of the ideality of both
outer and inner sense, and therefore of all objects of the senses,
as mere appearances, it is especially relevant to observe that
everything in our knowledge which belongs to intuition --
feeling of pleasure and pain, and the will, not being know-
ledge, are excluded -- contains nothing but mere relations;
namely, of locations in an intuition (extension), of change
of location (motion), and of laws according to which this
change is determined (moving forces). What it is that is
present in this or that location, or what it is that is operative
in the things themselves apart from change of location, is not
given through intuition. Now a thing in itself cannot be
known through mere relations; and we may therefore conclude
that since outer sense gives us nothing but mere relations, this
sense can contain in its representation only the relation of an
object to the subject, and not the inner properties of the object
in itself. This also holds true of inner sense, not only because
the representations of the outer senses constitute the proper
material with which we occupy our mind, but because the
time in which we set these representations, which is itself ante-
cedent to the consciousness of them in experience, and which
underlies them as the formal condition of the mode in which
we posit them in the mind, itself contains [only] relations of
succession, coexistence, and of that which is coexistent with
succession, the enduring. Now that which, as representation,
can be antecedent to any and every act of thinking any-
thing, is intuition; and if it contains nothing but relations, it
is the form of intuition. Since this form does not represent
anything save in so far as something is posited in the mind, it
can be nothing but the mode in which the mind is affected
through its own activity (namely, through this positing of its
representation), and so is affected by itself; in other words, it is
P 088
nothing but an inner sense in respect of the form of that sense. 
Everything that is represented through a sense is so far always
appearance, and consequently we must either refuse to admit
that there is an inner sense, or we must recognise that the sub-
ject, which is the object of the sense, can be represented through
it only as appearance, not as that subject would judge of itself
if its intuition were self-activity only, that is, were intellectual. 
The whole difficulty is as to how a subject can inwardly intuit
itself; and this is a difficulty common to every theory. The con-
sciousness of self (apperception) is the simple representation
of the 'I', and if all that is manifold in the subject were given
by the activity of the self, the inner intuition would be intel-
lectual. In man this consciousness demands inner perception
of the manifold which is antecedently given in the subject,
and the mode in which this manifold is given in the mind
must, as non-spontaneous, be entitled sensibility. If the
faculty of coming to consciousness of oneself is to seek out (to
apprehend) that which lies in the mind, it must affect the mind,
and only in this way can it give rise to an intuition of itself. 
But the form of this intuition, which exists antecedently in the
mind, determines, in the representation of time, the mode in
which the manifold is together in the mind, since it then in-
tuits itself not as it would represent itself if immediately self-
active, but as it is affected by itself, and therefore as it appears
to itself, not as it is. 
III. When I say that the intuition of outer objects and the
self-intuition of the mind alike represent the objects and the
mind, in space and in time, as they affect our senses, that is, as
they appear, I do not mean to say that these objects are a mere
illusion. For in an appearance the objects, nay even the pro-
perties that we ascribe to them, are always regarded as some-
thing actually given. Since, however, in the relation of the
given object to the subject, such properties depend upon the
mode of intuition of the subject, this object as appearance is to
be distinguished from itself as object in itself. Thus when I
maintain that the quality of space and of time, in conformity
with which, as a condition of their existence, I posit both bodies
and my own soul, lies in my mode of intuition and not in those
objects in themselves, I am not saying that bodies merely seem
P 089
to be outside me, or that my soul only seems to be given in my self-
consciousness. It would be my own fault, if out of that which
I ought to reckon as appearance, I made mere illusion. That
does not follow as a consequence of our principle of the ideality
of all our sensible intuitions -- quite the contrary. It is only if we
ascribe objective reality to these forms of representation, that
it becomes impossible for us to prevent everything being
thereby transformed into mere illusion. For if we regard space
and time as properties which, if they are to be possible at all,
must be found in things in themselves, and if we reflect on the
absurdities in which we are then involved, in that two infinite
things, which are not substances, nor anything actually in-
hering in substances, must yet have existence, nay, must
be the necessary condition of the existence of all things, and
moreover must continue to exist, even although all existing
things be removed, -- we cannot blame the good Berkeley
for degrading bodies to mere illusion. Nay, even our own
existence, in being made thus dependent upon the self-sub-
sistent reality of a non-entity, such as time, would necessarily
be changed with it into sheer illusion -- an absurdity of which
no one has yet been guilty. 
 The predicates of the appearance can be ascribed to the object
itself, in relation to our sense, for instance, the red colour or the
scent to the rose. But what is illusory can never be ascribed as
predicate to an object (for the sufficient reason that we then attribute
to the object, taken by itself, what belongs to it only in relation to
the senses, or in general to the subject), for instance, the two handles
which were formerly ascribed to Saturn. That which, while in-
separable from the representation of the object, is not to be met
with in the object in itself, but always in its relation to the subject,
is appearance. Accordingly the predicates of space and time are
rightly ascribed to the objects of the senses, as such; and in this there
is no illusion. On the other hand, if I describe redness to the rose in
itself [handles to Satum], or extension to all outer objects in them-
selves, without paying regard to the determinate relation of these
objects to the subject, and without limiting my judgment to that
relation, illusion then first arises. 
P 089
 IV. In natural theology, in thinking an object [God],
who not only can never be an object of intuition to us but
P 090
cannot be an object of sensible intuition even to himself, we
are careful to remove the conditions of time and space from
his intuition -- for all his knowledge must be intuition, and not
thought, which always involves limitations. But with what
right can we do this if we have previously made time and space
forms of things in themselves, and such as would remain, as
a priori conditions of the existence of things, even though the
things themselves were removed? As conditions of all existence
in general, they must also be conditions of the existence of
God. If we do not thus treat them as objective forms of all
things, the only alternative is to view them as subjective forms
of our inner and outer intuition, which is termed sensible, for
the very reason that it is not original, that is, is not such as can
itself give us the existence of its object -- a mode of intuition
which, so far as we can judge, can belong only to the prim-
ordial being. Our mode of intuition is dependent upon the
existence of the object, and is therefore possible only if the
subject's faculty of representation is affected by that object. 
This mode of intuiting in space and time need not be
limited to human sensibility. It may be that all finite, thinking
beings necessarily agree with man in this respect, although
we are not in a position to judge whether this is actually so. But
however universal this mode of sensibility may be, it does
not therefore cease to be sensibility. It is derivative (intuitus
derivativus), not original (intuitus originarius), and therefore
not an intellectual intuition. For the reason stated above, such
intellectual intuition seems to belong solely to the primordial
being, and can never be ascribed to a dependent being,
dependent in its existence as well as in its intuition, and
which through that intuition determines its existence solely
in relation to given objects. This latter remark, however,
must be taken only as an illustration of our aesthetic theory,
not as forming part of the proof. 
 Conclusion of the Transcendental Aesthetic 
Here, then, in pure a priori intuitions, space and time,
we have one of the factors required for solution of the general
P 091
problem of transcendental philosophy: how are synthetic
a priori judgments possible?  When in a priori judgment
we seek to go out beyond the given concept, we come in the
a priori intuitions upon that which cannot be discovered in
the concept but which is certainly found a priori in the in-
tuition corresponding to the concept, and can be connected
with it synthetically. Such judgments, however, thus based
on intuition, can never extend beyond objects of the senses;
they are valid only for objects of possible experience.