Critique of Pure Reason

(Analytic of Concepts)

P 092
OUR knowledge springs from two fundamental sources of the
mind; the first is the capacity of receiving representations
(receptivity for impressions), the second is the power of know-
ing an object through these representations (spontaneity [in
the production] of concepts). Through the first an object is given
to us, through the second the object is thought in relation to
that [given] representation (which is a mere determination of
the mind). Intuition and concepts constitute, therefore, the ele-
ments of all our knowledge, so that neither concepts without an
intuition in some way corresponding to them, nor intuition with-
out concepts, can yield knowledge. Both may be either pure or
empirical. When they contain sensation (which presupposes the
actual presence of the object), they are empirical. When there is
no mingling of sensation with the representation,they are pure. 
Sensation may be entitled the material of sensible knowledge. 
Pure intuition, therefore, contains only the form under which
 something is intuited; the pure concept only the form of the
thought of an object in general. Pure intuitions or pure con-
cepts alone are possible a priori, empirical intuitions and
empirical concepts only a posteriori. 
P 093
If the receptivity of our mind, its power of receiving re-
presentations in so far as it is in any wise affected, is to be
entitled sensibility, then the mind's power of producing repre-
sentations from itself, the spontaneity of knowledge, should be
called the understanding. Our nature is so constituted that
our intuition can never be other than sensible; that is, it con-
tains only the mode in which we are affected by objects. The
faculty, on the other hand, which enables us to think the
object of sensible intuition is the understanding. To neither
of these powers may a preference be given over the other. 
Without sensibility no object would be given to us, without
understanding no object would be thought. Thoughts without
content are empty, intuitions without concepts are blind. It
is, therefore, just as necessary to make our concepts sensible,
that is, to add the object to them in intuition, as to make
our intuitions intelligible, that is, to bring them under con-
cepts. These two powers or capacities cannot exchange their
functions. The understanding can intuit nothing, the senses
can think nothing. Only through their union can know-
ledge arise. But that is no reason for confounding the
contribution of either with that of the other; rather is it
a strong reason for carefully separating and distinguishing
the one from the other. We therefore distinguish the science
of the rules of sensibility in general, that is, aesthetic, from
the science of the rules of the understanding in general, that
is, logic. 
Logic, again, can be treated in a twofold manner, either
as logic of the general or as logic of the special employment
of the understanding. The former contains the absolutely
necessary rules of thought without which there can be no
employment whatsoever of the understanding. It therefore
treats of understanding without any regard to difference in
the objects to which the understanding may be directed. The
logic of the special employment of the understanding contains
the rules of correct thinking as regards a certain kind of
objects. The former may be called the logic of elements, the
latter the organon of this or that science. The latter is com-
monly taught in the schools as a propaedeutic to the sciences,
though, according to the actual procedure of human reason,
it is what is obtained last of all, when the particular science
P 094
under question has been already brought to such completion
that it requires only a few finishing touches to correct and
perfect it. For the objects under consideration must already
be known fairly completely before it can be possible to pre-
scribe the rules according to which a science of them is to
be obtained. 
 General logic is either pure or applied. In the former we
abstract from all empirical conditions under which our under-
standing is exercised, i.e. from the influence of the senses, the
play of imagination, the laws of memory, the force of habit,
inclination, etc. , and so from all sources of prejudice, indeed
from all causes from which this or that knowledge may arise
or seem to arise. For they concern the understanding only in
so far as it is being employed under certain circumstances,
and to become acquainted with these circumstances experi-
ence is required. Pure general logic has to do, therefore, only
with principles a priori, and is a canon of understanding and
of reason, but only in respect of what is formal in their em-
ployment, be the content what it may, empirical or tran-
scendental. General logic is called applied, when it is directed
to the rules of the employment of understanding under the
subjective empirical conditions dealt with by psychology. 
Applied logic has therefore empirical principles, although it
is still indeed in so far general that it refers to the employ-
ment of the understanding without regard to difference in the
objects. Consequently it is neither a canon of the under-
standing in general nor an organon of special sciences, but
merely a cathartic of the common understanding. 
In general logic, therefore, that part which is to constitute
the pure doctrine of reason must be entirely separated from
that which constitutes applied (though always still general)
logic. The former alone is, properly speaking, a science,
though indeed concise and dry, as the methodical exposition
of a doctrine of the elements of the understanding is bound
to be. There are therefore two rules which logicians must
always bear in mind, in dealing with pure general logic:
1. As general logic, it abstracts from all content of the
knowledge of understanding and from all differences in its
objects, and deals with nothing but the mere form of
P 095
2. As pure logic, it has nothing to do with empirical prin-
ciples, and does not, as has sometimes been supposed, borrow
anything from psychology, which therefore has no influence
whatever on the canon of the understanding. Pure logic is a
body of demonstrated doctrine, and everything in it must be
certain entirely a priori. 
What I call applied logic (contrary to the usual meaning
of this title, according to which it should contain certain
exercises for which pure logic gives the rules) is a representa-
tion of the understanding and of the rules of its necessary
employment in concreto, that is, under the accidental sub-
jective conditions which may hinder or help its application,
and which are all given only empirically. It treats of attention,
its impediments and consequences, of the source of error, of
the state of doubt, hesitation, and conviction, etc. Pure general
logic stands to it in the same relation as pure ethics, which
contains only the necessary moral laws of a free will in general,
stands to the doctrine of the virtues strictly so called -- the
doctrine which considers these laws under the limitations of
the feelings, inclinations, and passions to which men are
more or less subject. Such a doctrine can never furnish a
true and demonstrated science, because, like applied logic,
it depends on empirical and psychological principles. 
General logic, as we have shown, abstracts from all con-
tent of knowledge, that is, from all relation of knowledge to
the object, and considers only the logical form in the relation of
any knowledge to other knowledge; that is, it treats of the form
of thought in general. But since, as the Transcendental Aes-
thetic has shown, there are pure as well as empirical intuitions,
a distinction might likewise be drawn between pure and em-
pirical thought of objects. In that case we should have a logic
in which we do not abstract from the entire content of know-
ledge. This other logic, which should contain solely the rules
of the pure thought of an object, would exclude only those
P 096
modes of knowledge which have empirical content. It would
also treat of the origin of the modes in which we know objects,
in so far as that origin cannot be attributed to the objects. 
General logic, on the other hand, has nothing to do with the
origin of knowledge, but only considers representations, be
they originally a priori in ourselves or only empirically given,
according to the laws which the understanding employs when,
in thinking, it relates them to one another. It deals therefore
only with that form which the understanding is able to impart
to the representations, from whatever source they may have
And here I make a remark which the reader must bear
well in mind, as it extends its influence over all that follows. 
Not every kind of knowledge a priori should be called tran-
scendental, but that only by which we know that -- and how --
certain representations (intuitions or concepts) can be em-
ployed or are possible purely a priori. The term 'transcend-
ental', that is to say, signifies such knowledge as concerns the
a priori possibility of knowledge, or its a priori employment. 
Neither space nor any a priori geometrical determination of it
is a transcendental representation; what can alone be entitled
transcendental is the knowledge that these representations are
not of empirical origin, and the possibility that they can yet
relate a priori to objects of experience. The application of
space to objects in general would likewise be transcendental,
but, if restricted solely to objects of sense, it is empirical. 
The distinction between the transcendental and the empirical
belongs therefore only to the critique of knowledge; it does
not concern the relation of that knowledge to its objects. 
In the expectation, therefore, that there may perhaps be
concepts which relate a priori to objects, not as pure or sen-
sible intuitions, but solely as acts of pure thought -- that is, as
concepts which are neither of empirical nor of aesthetic
origin -- we form for ourselves by anticipation the idea of a
science of the knowledge which belongs to pure understanding
and reason, whereby we think objects entirely a priori. Such
a science, which should determine the origin, the scope, and
P 097
the objective validity of such knowledge, would have to be
called transcendental logic, because, unlike general logic,
which has to deal with both empirical and pure knowledge of
reason, it concerns itself with the laws of understanding and
of reason solely in so far as they relate a priori to objects. 
The question, famed of old, by which logicians were
supposed to be driven into a corner, obliged either to have
recourse to a pitiful sophism, or to confess their ignorance
and consequently the emptiness of their whole art, is the
question: What is truth? The nominal definition of truth,
that it is the agreement of knowledge with its object, is
assumed as granted; the question asked is as to what is
the general and sure criterion of the truth of any and every
To know what questions may reasonably be asked is
already a great and necessary proof of sagacity and insight. 
For if a question is absurd in itself and calls for an answer
where none is required, it not only brings shame on the pro-
pounder of the question, but may betray an incautious listener
into absurd answers, thus presenting, as the ancients said, the
ludicrous spectacle of one man milking a he-goat and the
other holding a sieve underneath. 
If truth consists in the agreement of knowledge with its
object, that object must thereby be distinguished from other
objects; for knowledge is false, if it does not agree with the
object to which it is related, even although it contains some-
thing which may be valid of other objects. Now a general
criterion of truth must be such as would be valid in each and
every instance of knowledge, however their objects may vary. It
is obvious, however, that such a criterion [being general] cannot
take account of the [varying] content of knowledge (relation
to its [specific] object). But since truth concerns just this very
content, it is quite impossible, and indeed absurd, to ask for a
P 098
general test of the truth of such content. A sufficient and at the
same time general criterion of truth cannot possibly be given. 
Since we have already entitled the content of knowledge its
matter, we must be prepared to recognise that of the truth
of knowledge, so far as its matter is concerned, no general
criterion can be demanded. Such a criterion would by its
very nature be self-contradictory. 
But, on the other hand, as regards knowledge in respect
of its mere form (leaving aside all content), it is evident that
logic, in so far as it expounds the universal and necessary
rules of the understanding, must in these rules furnish criteria
of truth. Whatever contradicts these rules is false. For the
understanding would thereby be made to contradict its own
general rules of thought, and so to contradict itself. These
criteria, however, concern only the form of truth, that is, of
thought in general; and in so far they are quite correct, but
are not by themselves sufficient. For although our knowledge
may be in complete accordance with logical demands, that is,
may not contradict itself, it is still possible that it may be in
contradiction with its object. The purely logical criterion of
truth, namely, the agreement of knowledge with the general
and formal laws of the understanding and reason, is a conditio
sine qua non, and is therefore the negative condition of all
truth. But further than this logic cannot go. It has no touch-
stone for the discovery of such error as concerns not the
form but the content. 
General logic resolves the whole formal procedure of the
understanding and reason into its elements, and exhibits them
as principles of all logical criticism of our knowledge. This
part of logic, which may therefore be entitled analytic, yields
what is at least the negative touchstone of truth. Its rules
must be applied in the examination and appraising of the
form of all knowledge before we proceed to determine whether
their content contains positive truth in respect to their object. 
But since the mere form of knowledge, however completely
it may be in agreement with logical laws, is far from being
sufficient to determine the material (objective) truth of know-
ledge, no one can venture with the help of logic alone to
judge regarding objects, or to make any assertion. We must
first, independently of logic, obtain reliable information; only
P 099
then are we in a position to enquire, in accordance with logical
laws, into the use of this information and its connection in a
coherent whole, or rather to test it by these laws. There is,
however, something so tempting in the possession of an art so
specious, through which we give to all our knowledge, how-
ever uninstructed we may be in regard to its content, the form
of understanding, that general logic, which is merely a canon
of judgment, has been employed as if it were an organon for
the actual production of at least the semblance of objective
assertions, and has thus been misapplied. General logic, when
thus treated as an organon, is called dialectic. 
However various were the significations in which the ancients
used 'dialectic' as the title for a science or art, we can safely
conclude from their actual employment of it that with them
it was never anything else than the logic of illusion. It was a
sophistical art of giving to ignorance, and indeed to intentional
sophistries, the appearance of truth, by the device of imitat-
ing the methodical thoroughness which logic prescribes, and
of using its 'topic' to conceal the emptiness of its pretensions. 
Now it may be noted as a sure and useful warning, that general
logic, if viewed as an organon, is always a logic of illusion,
that is, dialectical. For logic teaches us nothing whatsoever
regarding the content of knowledge, but lays down only the
formal conditions of agreement with the understanding; and
since these conditions can tell us nothing at all as to the
objects concerned, any attempt to use this logic as an instru-
ment (organon) that professes to extend and enlarge our
knowledge can end in nothing but mere talk -- in which, with
a certain plausibility, we maintain, or, if such be our choice,
attack, any and every possible assertion. 
Such instruction is quite unbecoming the dignity of philo-
sophy. The title 'dialectic' has therefore come to be otherwise
employed, and has been assigned to logic, as a critique of
dialectical illusion. This is the sense in which it is to be under-
stood in this work. 
P 100
In a transcendental logic we isolate the understanding --
as above, in the Transcendental Aesthetic, the sensibility --
separating out from our knowledge that part of thought which
has its origin solely in the understanding. The employment of
this pure knowledge depends upon the condition that objects
to which it can be applied be given to us in intuition. In the
absence of intuition all our knowledge is without objects,
and therefore remains entirely empty. That part of transcen-
dental logic which deals with the elements of the pure know-
ledge yielded by understanding, and the principles without
which no object can be thought, is transcendental analytic. It
is a logic of truth. For no knowledge can contradict it without
at once losing all content, that is, all relation to any object, and
therefore all truth. But since it is very tempting to use these
pure modes of knowledge of the understanding and these prin-
ciples by themselves, and even beyond the limits of experience,
which alone can yield the matter (objects) to which those pure
concepts of understanding can be applied, the understanding is
led to incur the risk of making, with a mere show of rationality,
a material use of its pure and merely formal principles, and of
passing judgments upon objects without distinction -- upon
objects which are not given to us, nay, perhaps cannot in any
way be given. Since, properly, this transcendental analytic
should be used only as a canon for passing judgment upon the
empirical employment of the understanding, it is misapplied
if appealed to as an organon of its general and unlimited
application, and if consequently we venture, with the pure
understanding alone, to judge synthetically, to affirm, and to
decide regarding objects in general. The employment of the
pure understanding then becomes dialectical. The second part
of transcendental logic must therefore form a critique of this
dialectical illusion, and is called transcendental dialectic, not
as an art of producing such illusion dogmatically (an art un-
fortunately very commonly practised by metaphysical jugglers),
but as a critique of understanding and reason in respect of
P 101
their hyperphysical employment. It will expose the false, illu-
sory character of those groundless pretensions, and in place
of the high claims to discover and to extend knowledge merely
by means of transcendental principles, it will substitute what is
no more than a critical treatment of the pure understanding,
for the guarding of it against sophistical illusion. 
P 102
TRANSCENDENTAL analytic consists in the dissection of all
our a priori knowledge into the elements that pure under-
standing by itself yields. In so doing, the following are the
points of chief concern: (1) that the concepts be pure and
not empirical; (2) that they belong, not to intuition and
sensibility, but to thought and understanding; (3) that
they be fundamental and be carefully distinguished from
those which are derivative or composite; (4) that our table
of concepts be complete, covering the whole field of the pure
understanding. When a science is an aggregate brought into
existence in a merely experimental manner, such completeness
can never be guaranteed by any kind of mere estimate. It is
possible only by means of an idea of the totality of the a priori
knowledge yielded by the understanding; such an idea can
furnish an exact classification of the concepts which compose
that totality, exhibiting their interconnection in a system. 
Pure understanding distinguishes itself not merely from all
that is empirical but completely also from all sensibility. It
is a unity self-subsistent, self-sufficient, and not to be increased
by any additions from without. The sum of its knowledge thus
constitutes a system, comprehended and determined by one
idea. The completeness and articulation of this system can at
the same time yield a criterion of the correctness and genuine-
ness of all its components. This part of transcendental logic
requires, however, for its complete exposition, two books, the
one containing the concepts, the other the principles of pure
P 103
By 'analytic of concepts' I do not understand their ana-
lysis, or the procedure usual in philosophical investigations,
that of dissecting the content of such concepts as may present
themselves, and so of rendering them more distinct; but the
hitherto rarely attempted dissection of the faculty of the under-
standing itself, in order to investigate the possibility of con-
cepts a priori by looking for them in the understanding alone,
as their birthplace, and by analysing the pure use of this
faculty. This is the proper task of a transcendental philosophy;
anything beyond this belongs to the logical treatment of con-
cepts in philosophy in general. We shall therefore follow up
the pure concepts to their first seeds and dispositions in the
human understanding, in which they lie prepared, till at last,
on the occasion of experience, they are developed, and by the
same understanding are exhibited in their purity, freed from
the empirical conditions attaching to them. 
P 104
WHEN we call a faculty of knowledge into play, then,
as the occasioning circumstances differ, various concepts
stand forth and make the faculty known, and allow of
their being collected with more or less completeness, in
proportion as observation has been made of them over a longer
time or with greater acuteness. But when the enquiry is
carried on in this mechanical fashion, we can never be sure
whether it has been brought to completion. Further, the con-
cepts which we thus discover only as opportunity offers, ex-
hibit no order and systematic unity, but are in the end merely
arranged in pairs according to similarities, and in series accord-
ing to the amount of their contents, from the simple on to the
more composite -- an arrangement which is anything but sys-
tematic, although to a certain extent methodically instituted. 
Transcendental philosophy, in seeking for its concepts, has
the advantage and also the duty of proceeding according to a
single principle. For these concepts spring, pure and unmixed,
out of the understanding which is an absolute unity; and must
therefore be connected with each other according to one con-
cept or idea. Such a connection supplies us with a rule, by
which we are enabled to assign its proper place to each pure
concept of the understanding, and by which we can determine
in an a priori manner their systematic completeness. Other-
wise we should be dependent in these matters on our own
discretionary judgment or merely on chance. 
P 105
Section I
The understanding has thus far been explained merely
negatively, as a non-sensible faculty of knowledge. Now since
without sensibility we cannot have any intuition, understand-
ing cannot be a faculty of intuition. But besides intuition there
is no other mode of knowledge except by means of concepts. 
The knowledge yielded by understanding, or at least by the
human understanding, must therefore be by means of concepts,
and so is not intuitive, but discursive. Whereas all intuitions,
as sensible, rest on affections, concepts rest on functions. By
'function' I mean the unity of the act of bringing various repre-
sentations under one common representation. Concepts are
based on the spontaneity of thought, sensible intuitions on the
receptivity of impressions. Now the only use which the under-
standing can make of these concepts is to judge by means of
them. Since no representation, save when it is an intuition,
is in immediate relation to an object, no concept is ever
related to an object immediately, but to some other representa-
tion of it, be that other representation an intuition, or itself
a concept. Judgment is therefore the mediate knowledge of an
object, that is, the representation of a representation of it. In
every judgment there is a concept which holds of many repre-
sentations, and among them of a given representation that is
immediately related to an object. Thus in the judgment, 'all
bodies are divisible', the concept of the divisible applies to
various other concepts, but is here applied in particular to
the concept of body, and this concept again to certain appear-
ances that present themselves to us. These objects, therefore,
are mediately represented through the concept of divisibility. 
Accordingly, all judgments are functions of unity among our
P 106
representations; instead of an immediate representation, a
higher representation, which comprises the immediate repre-
sentation and various others, is used in knowing the object,
and thereby much possible knowledge is collected into one. 
Now we can reduce all acts of the understanding to judg-
ments, and the understanding may therefore be represented
as a faculty of judgment. For, as stated above, the under-
standing is a faculty of thought. Thought is knowledge by
means of concepts. But concepts, as predicates of possible
judgments, relate to some representation of a not yet deter-
mined object. Thus the concept of body means something, for
instance, metal, which can be known by means of that con-
cept. It is therefore a concept solely in virtue of its com-
prehending other representations, by means of which it can
relate to objects. It is therefore the predicate of a possible
judgment, for instance, 'every metal is a body'. The functions
of the understanding can, therefore, be discovered if we can
give an exhaustive statement of the functions of unity in
judgments. That this can quite easily be done will be shown
in the next section. 
Section 2
If we abstract from all content of a judgment, and con-
sider only the mere form of understanding, we find that the
function of thought in judgment can be brought under four
heads, each of which contains three moments. They may be
conveniently represented in the following table:
P 107
Quantity of Judgments
Singular II III
Quality Relation
Affirmative Categorical
Negative Hypothetical
Infinite Disjunctive 
As this division appears to depart in some, though not in
any essential respects, from the technical distinctions ordin-
arily recognised by logicians, the following observations may
serve to guard against any possible misunderstanding. 
1. Logicians are justified in saying that, in the employ-
ment of judgments in syllogisms, singular judgments can
be treated like those that are universal. For, since they
have no extension at all, the predicate cannot relate to part
only of that which is contained in the concept of the subject,
and be excluded from the rest. The predicate is valid of that
concept, without any such exception, just as if it were a
general concept and had an extension to the whole of which
the predicate applied. If, on the other hand, we compare a
singular with a universal judgment, merely as knowledge,
in respect of quantity, the singular stands to the universal as
unity to infinity, and is therefore in itself essentially different
from the universal. If, therefore, we estimate a singular judg-
ment (judicium singulare), not only according to its own inner
validity, but as knowledge in general, according to its quantity
in comparison with other knowledge, it is certainly different
from general judgments (judicia communia), and in a com-
plete table of the moments of thought in general deserves a
separate place -- though not, indeed, in a logic limited to the
use of judgments in reference to each other. 
P 108
2. In like manner infinite judgments must, in trans-
cendental logic, be distinguished from those that are affirm-
ative, although in general logic they are rightly classed with
them, and do not constitute a separate member of the division. 
General logic abstracts from all content of the predicate (even
though it be negative); it enquires only whether the predicate
be ascribed to the subject or opposed to it. But transcendental
logic also considers what may be the worth or content of a
logical affirmation that is thus made by means of a merely
negative predicate, and what is thereby achieved in the way
of addition to our total knowledge. If I should say of the soul,
'It is not mortal', by this negative judgment I should at least
have warded off error. Now by the proposition, 'The soul
is non-mortal', I have, so far as the logical form is concerned,
really made an affirmation. I locate the soul in the unlimited
sphere of non-mortal beings. Since the mortal constitutes
one part of the whole extension of possible beings, and the
non-mortal the other, nothing more is said by my proposition
than that the soul is one of the infinite number of things which
remain over when I take away all that is mortal. The infinite
sphere of all that is possible is thereby only so far limited that
the mortal is excluded from it, and that the soul is located
in the remaining part of its extension. But, even allowing
for such exclusion, this extension still remains infinite, and
several more parts of it may be taken away without the con-
cept of the soul being thereby in the least increased, or de-
termined in an affirmative manner. These judgments, though
infinite in respect of their logical extension, are thus, in respect
of the content of their knowledge, limitative only, and cannot
therefore be passed over in a transcendental table of all
moments of thought in judgments, since the function of the
understanding thereby expressed may perhaps be of import-
ance in the field of its pure a priori knowledge. 
3. All relations of thought in judgments are (a) of the
predicate to the subject, (b) of the ground to its consequence,
(c) of the divided knowledge and of the members of the
division, taken together, to each other. In the first kind of
P 109
judgments we consider only two concepts, in the second
two judgments, in the third several judgments in their relation
to each other. The hypothetical proposition, 'If there is a
perfect justice, the obstinately wicked are punished', really
contains the relation of two propositions, namely, 'There is
a perfect justice', and 'The obstinately wicked are punished'. 
Whether both these propositions are in themselves true, here
remains undetermined. It is only the logical sequence which
is thought by this judgment. Finally, the disjunctive judgment
contains a relation of two or more propositions to each other,
a relation not, however, of logical sequence, but of logical
opposition, in so far as the sphere of the one excludes the
sphere of the other, and yet at the same time of community,
in so far as the propositions taken together occupy the whole
sphere of the knowledge in question. The disjunctive judg-
ment expresses, therefore, a relation of the parts of the sphere
of such knowledge, since the sphere of each part is a com-
plement of the sphere of the others, yielding together the
sum-total of the divided knowledge. Take, for instance, the
judgment, 'The world exists either through blind chance,
or through inner necessity, or through an external cause'. 
Each of these propositions occupies a part of the sphere of
the possible knowledge concerning the existence of a world in
general; all of them together occupy the whole sphere. To
take the knowledge out of one of these spheres means placing
it in one of the other spheres, and to place it in one sphere
means taking it out of the others. There is, therefore, in a
disjunctive judging a certain community of the known
constitutes, such that they mutually exclude each other,
and yet thereby determine in their totality the true know-
ledge. For, when taken together, they constitute the whole
content of one given knowledge. This is all that need here
be considered, so far as concerns what follows. 
4. The modality of judgments is a quite peculiar function. 
Its distinguishing characteristic is that it contributes nothing
to the content of the judgment (for, besides quantity, quality,
and relation, there is nothing that constitutes the content of
a judgment), but concerns only the value of the copula in
relation to thought in general. Problematic judgments are
those in which affirmation or negation is taken as merely
P 110
possible (optional). In assertoric judgments affirmation or
negation is viewed as real (true), and in apodeictic judgments
as necessary. Thus the two judgments, the relation of which
constitutes the hypothetical judgment (antecedens et con-
sequens), and likewise the judgments the reciprocal relation
of which forms the disjunctive judgment (members of the
division), are one and all problematic only. In the above
example, the proposition, 'There is a perfect justice', is not
stated assertorically, but is thought only as an optional judg-
ment, which it is possible to assume; it is only the logical
sequence which is assertoric. Such judgments may therefore
be obviously false, and yet, taken problematically, may be con-
ditions of the knowledge of truth. Thus the judgment 'The
world exists by blind chance', has in the disjunctive judgment
only problematic meaning, namely, as a proposition that may
for a moment be assumed. At the same time, like the indica-
tion of a false road among the number of all those roads that
can be taken, it aids in the discovery of the true proposition. 
The problematic proposition is therefore that which expresses
only logical (which is not objective) possibility -- a free choice
of admitting such a proposition, and a purely optional
admission of it into the understanding. The assertoric pro-
position deals with logical reality or truth. Thus, for instance,
in a hypothetical syllogism the antecedent is in the major
premiss problematic, in the minor assertoric, and what the
syllogism shows is that the consequence follows in accordance
with the laws of the understanding. The apodeictic proposi-
tion thinks the assertoric as determined by these laws of the
understanding, and therefore as affirming a priori; and in
this manner it expresses logical necessity. Since everything
is thus incorporated in the understanding step by step -- inas-
much as we first judge something problematically, then
maintain its truth assertorically, and finally affirm it as in-
separably united with the understanding, that is, as necessary
and apodeictic -- we are justified in regarding these three
functions of modality as so many moments of thought. 
 Just as if thought were in the problematic a function of the
understanding; in the assertoric, of the faculty of judgment; in
the apodeictic, of reason. This is a remark which will be explained
in the sequel. 
P 111
Section 3
General logic, as has been repeatedly said, abstracts from
all content of knowledge, and looks to some other source,
whatever that may be, for the representations which it is
to transform into concepts by process of analysis. Tran-
scendental logic, on the other hand, has lying before it a mani-
fold of a priori sensibility, presented by transcendental aes-
thetic, as material for the concepts of pure understanding. 
In the absence of this material those concepts would be with-
out any content, therefore entirely empty. Space and time
contain a manifold of pure a priori intuition, but at the same
time are conditions of the receptivity of our mind -- conditions
under which alone it can receive representations of objects, and
which therefore must also always affect the concept of these
objects. But if this manifold is to be known, the spontaneity
of our thought requires that it be gone through in a certain
way, taken up, and connected. This act I name synthesis. 
By synthesis, in its most general sense, I understand the
act of putting different representations together, and of grasp-
ing what is manifold in them in one [act of] knowledge. Such
a synthesis is pure, if the manifold is not empirical but is given
a priori, as is the manifold in space and time. Before we can
analyse our representations, the representations must them-
selves be given, and therefore as regards content no concepts
can first arise by way of analysis. Synthesis of a manifold (be
it given empirically or a priori) is what first gives rise to know-
ledge. This knowledge may, indeed, at first, be crude and con-
fused, and therefore in need of analysis. Still the synthesis is
that which gathers the elements for knowledge, and unites
them to [form] a certain content. It is to synthesis, therefore,
P 112
that we must first direct our attention, if we would determine
the first origin of our knowledge. 
Synthesis in general, as we shall hereafter see, is the mere
result of the power of imagination, a blind but indispensable
function of the soul, without which we should have no know-
ledge whatsoever, but of which we are scarcely ever conscious. 
To bring this synthesis to concepts is a function which belongs
to the understanding, and it is through this function of the
understanding that we first obtain knowledge properly so
Pure synthesis, represented in its most general aspect, gives
the pure concept of the understanding. By this pure syn-
thesis I understand that which rests upon a basis of a priori
synthetic unity. Thus our counting, as is easily seen in the case
of larger numbers, is a synthesis according to concepts, be-
cause it is executed according to a common ground of unity,
as, for instance, the decade. In terms of this concept, the unity
of the synthesis of the manifold is rendered necessary. 
By means of analysis different representations are brought
under one concept -- a procedure treated of in general logic. 
What transcendental logic, on the other hand, teaches, is how
we bring to concepts, not representations, but the pure syn-
thesis of representations. What must first be given -- with a
view to the a priori knowledge of all objects -- is the manifold
of pure intuition; the second factor involved is the synthesis of
this manifold by means of the imagination. But even this does
not yet yield knowledge. The concepts which give unity to this
pure synthesis, and which consist solely in the representation
of this necessary synthetic unity, furnish the third requisite for
the knowledge of an object; and they rest on the under-
The same function which gives unity to the various repre-
sentations in a judgment also gives unity to the mere syn-
thesis of various representations in an intuition; and this
unity, in its most general expression, we entitle the pure con-
cept of the understanding. The same understanding, through
the same operations by which in concepts, by means of ana-
lytical unity, it produced the logical form of a judgment,
also introduces a transcendental content into its representa-
tions, by means of the synthetic unity of the manifold in intui-
P 113
tion in general. On this account we are entitled to call these
representations pure concepts of the understanding, and to
regard them as applying a priori to objects -- a conclusion
which general logic is not in a position to establish. 
In this manner there arise precisely the same number of
pure concepts of the understanding which apply a priori to
objects of intuition in general, as, in the preceding table, there
have been found to be logical functions in all possible judg-
ments. For these functions specify the understanding com-
pletely, and yield an exhaustive inventory of its powers. These
concepts we shall, with Aristotle, call categories, for our
primary purpose is the same as his, although widely diverging
from it in manner of execution. 
Of Quantity
Of Quality Of Relation
Reality Of Inherence and Subsistence
Negation (substantia et accidens)
Limitation Of Causality and Dependence
(cause and effect)
Of Community (reciprocity
between agent and patient) 
Of Modality
Possibility -- Impossibility
Existence -- Non-existence
Necessity -- Contingency 
This then is the list of all original pure concepts of syn-
thesis that the understanding contains within itself a priori. 
P 114
Indeed, it is because it contains these concepts that it is
called pure understanding; for by them alone can it under-
stand anything in the manifold of intuition, that is, think an
object of intuition. This division is developed systematically
from a common principle, namely, the faculty of judgment
(which is the same as the faculty of thought). It has not arisen
rhapsodically, as the result of a haphazard search after pure
concepts, the complete enumeration of which as based on
induction only, could never be guaranteed. Nor could we, if
this were our procedure, discover why just these concepts, and
no others, have their seat in the pure understanding. It was
an enterprise worthy of an acute thinker like Aristotle to make
search for these fundamental concepts. But as he did so on no
principle, he merely picked them up as they came his way,
and at first procured ten of them, which he called categories
(predicaments). Afterwards he believed that he had discovered
five others, which he added under the name of post-predica-
ments. But his table still remained defective. Besides, there
are to be found in it some modes of pure sensibility (quando,
ubi, situs, also prius, simul), and an empirical concept (motus),
none of which have any place in a table of the concepts that
trace their origin to the understanding. Aristotle's list also
enumerates among the original concepts some derivative con-
cepts (actio, passio); and of the original concepts some are
entirely lacking. 
In this connection, it is to be remarked that the categories,
as the true primary concepts of the pure understanding, have
also their pure derivative concepts. These could not be passed
over in a complete system of transcendental philosophy, but
in a merely critical essay the simple mention of the fact may
 I beg permission to entitle these pure but derivative con-
cepts of the understanding the predicables of the pure under-
standing -- to distinguish them from the predicaments [i.e. the
categories]. If we have the original and primitive concepts, it
is easy to add the derivative and subsidiary, and so to give a
complete picture of the family tree of the [concepts of] pure
understanding. Since at present we are concerned not with the
completeness of the system, but only with the principles to be
followed in its construction, I reserve this supplementary work
P 115
for another occasion. It can easily be carried out, with the
aid of the ontological manuals -- for instance, by placing under
the category of causality the predicables of force, action,
passion; under the category of community the predicables
of presence, resistance; under the predicaments of modality
the predicables of coming to be, ceasing to be, change, etc. 
The categories, when combined with the modes of pure sen-
sibility, or with one another, yield a large number of derivative
a priori concepts. To note, and, where possible, to give a com-
plete inventory of these concepts, would be a useful and not
unpleasant task, but it is a task from which we can here be
In this treatise, I purposely omit the definitions of the cate-
gories, although I may be in possession of them. I shall pro-
ceed to analyse these concepts only so far as is necessary in
connection with the doctrine of method which I am propound-
ing. In a system of pure reason, definitions of the categories
would rightly be demanded, but in this treatise they would
merely divert attention from the main object of the enquiry,
arousing doubts and objections which, without detriment to
what is essential to our purposes, can very well be reserved for
another occasion. Meanwhile, from the little that I have said,
it will be obvious that a complete glossary, with all the requisite
explanations, is not only a possible, but an easy task. The divi-
sions are provided; all that is required is to fill them; and a
systematic 'topic', such as that here given, affords sufficient
guidance as to the proper location of each concept, while at
the same time indicating which divisions are still empty. 
This table of categories suggests some nice points, which
may perhaps have important consequences in regard to the
scientific form of all modes of knowledge obtainable by reason. 
For that this table is extremely useful in the theoretical part of
philosophy, and indeed is indispensable as supplying the com-
plete plan of a whole science, so far as that science rests on a -
priori concepts, and as dividing it systematically according to
P 116
determinate principles, is already evident from the fact that
the table contains all the elementary concepts of the under-
standing in their completeness, nay, even the form of a system
of them in the human understanding, and accordingly indi-
cates all the momenta of a projected speculative science, and
even their order, as I have elsewhere shown. 
P 116n
* Metaphysical First Principles of Natural Science. 
P 116
The first of the considerations suggested by the table is
that while it contains four classes of the concepts of under-
standing, it may, in the first instance, be divided into two
groups; those in the first group being concerned with objects
of intuition, pure as well as empirical, those in the second
group with the existence of these objects, in their relation
either to each other or to the understanding. 
The categories in the first group I would entitle the mathe-
matical, those in the second group the dynamical. The former
have no correlates; these are to be met with only in the second
group. This distinction must have some ground in the nature
of the understanding. 
Secondly, in view of the fact that all a priori division of
concepts must be by dichotomy, it is significant that in each
class the number of the categories is always the same, namely,
three. Further, it may be observed that the third category in
each class always arises from the combination of the second
category with the first. 
 Thus allness or totality is just plurality considered as unity;
limitation is simply reality combined with negation; commun-
ity is the causality of substances reciprocally determining one
another; lastly, necessity is just the existence which is given
through possibility itself. It must not be supposed, however,
that the third category is therefore merely a derivative, and
not a primary, concept of the pure understanding. For the com-
bination of the first and second concepts, in order that the third
may be produced, requires a special act of the understand-
ing, which is not identical with that which is exercised in the
case of the first and the second. Thus the concept of a number
(which belongs to the category of totality) is not always possible
simply upon the presence of concepts of plurality and unity
P 117
(for instance, in the representation of the infinite); nor can I,
by simply combining the concept of a cause and that of a sub-
stance, at once have understanding of influence, that is, how a
substance can be the cause of something in another substance. 
Obviously in these cases, a separate act of the understanding
is demanded; and similarly in the others. 
Thirdly, in the case of one category, namely, that of com-
munity, which is found in the third group, its accordance with
the form of a disjunctive judgment -- the form which corre-
sponds to it in the table of logical functions -- is not as evident
as in the case of the others. 
To gain assurance that they do actually accord, we must
observe that in all disjunctive judgments the sphere (that is,
the multiplicity which is contained in any one judgment) is
represented as a whole divided into parts (the subordinate con-
cepts), and that since no one of them can be contained under
any other, they are thought as co-ordinated with, not sub-
ordinated to, each other, and so as determining each other,
not in one direction only, as in a series, but reciprocally, as in
an aggregate -- if one member of the division is posited, all
the rest are excluded, and conversely. 
Now in a whole which is made up of things, a similar com-
bination is being thought; for one thing is not subordinated,
as effect, to another, as cause of its existence, but, simultane-
ously and reciprocally, is co-ordinated with it, as cause of the
determination of the other (as, for instance, in a body the
parts of which reciprocally attract and repel each other). This
is a quite different kind of connection from that which is found
in the mere relation of cause to effect (of ground to conse-
quence), for in the latter relation the consequence does not in
its turn reciprocally determine the ground, and therefore does
not constitute with it a whole -- thus the world, for instance,
does not with its Creator serve to constitute a whole. The
procedure which the understanding follows in representing to
itself the sphere of a divided concept it likewise follows when
it thinks a thing as divisible; and just as, in the former case,
the members of a division exclude each other, and yet are com-
P 118
bined in one sphere, so the understanding represents to itself
the parts of the latter as existing (as substances) in such a way
that, while each exists independently of the others, they are
yet combined together in one whole. 
In the transcendental philosophy of the ancients there is
included yet another chapter containing pure concepts of the
understanding which, though not enumerated among the cate-
gories, must, on their view, be ranked as a priori concepts of
objects. This, however, would amount to an increase in the
number of the categories, and is therefore not feasible. They
are propounded in the proposition, so famous among the
Schoolmen, quodlibet ens est unum, verum, bonum. Now,
although the application of this principle has proved very
meagre in consequences, and has indeed yielded only proposi-
tions that are tautological, and therefore in recent times has
retained its place in metaphysics almost by courtesy only, yet,
on the other hand, it represents a view which, however empty
it may seem to be, has maintained itself over this very long
period. It therefore deserves to be investigated in respect of
its origin, and we are justified in conjecturing that it has its
ground in some rule of the understanding which, as often
happens, has only been wrongly interpreted. These supposedly
transcendental predicates of things are, in fact, nothing but
logical requirements and criteria of all knowledge of things in
general, and prescribe for such knowledge the categories of
quantity, namely, unity, plurality, and totality. But these
categories, which, properly regarded, must be taken as material,
belonging to the possibility of the things themselves [empirical
objects], have, in this further application, been used only in
their formal meaning, as being of the nature of logical requis-
ites of all knowledge, and yet at the same time have been
incautiously converted from being criteria of thought to be pro-
perties of things in themselves. In all knowledge of an object
there is unity of concept, which may be entitled qualitative
unity, so far as we think by it only the unity in the combination
of the manifold of our knowledge: as, for example, the unity
of the theme in a play, a speech, or a story. Secondly, there is
P 119
truth, in respect of its consequences. The greater the number
of true consequences that follow from a given concept, the
more criteria are there of its objective reality. This might be
entitled the qualitative plurality of characters, which belong to
a concept as to a common ground (but are not thought in it, as
quantity). Thirdly, and lastly, there is perfection, which con-
sists in this, that the plurality together leads back to the unity
of the concept, and accords completely with this and with no
other concept. This may be entitled the qualitative complete-
ness (totality). Hence it is evident that these logical criteria of
the possibility of knowledge in general are the three categories
of quantity, in which the unity in the production of the quantum
has to be taken as homogeneous throughout; and that these
categories are here being transformed so as also to yield con-
nection of heterogeneous knowledge in one consciousness, by
means of the quality of the knowledge as the principle of the
connection. Thus the criterion of the possibility of a concept
(not of an object) is the definition of it, in which the unity of
the concept, the truth of all that may be immediately deduced
from it, and finally, the completeness of what has been thus de-
duced from it, yield all that is required for the construction of
the whole concept. Similarly, the criterion of an hypothesis
consists in the intelligibility of the assumed ground of explana-
tion, that is, in its unity (without any auxiliary hypothesis);
in the truth of the consequences that can be deduced from it
(their accordance with themselves and with experience); and
finally, in the completeness of the ground of explanation of
these consequences, which carry us back to neither more nor
less than was assumed in the hypothesis, and so in an a pos-
teriori analytic manner give us back and accord with what
has previously been thought in a synthetic a priori manner. 
We have not, therefore, in the concepts of unity, truth, and per-
fection, made any addition to the transcendental table of the
categories, as if it were in any respect imperfect. All that we
have done is to bring the employment of these concepts under
general logical rules, for the agreement of knowledge with
itself -- the question of their relation to objects not being in any
way under discussion. 
P 120
Section 1
JURISTS, when speaking of rights and claims, distinguish in a
legal action the question of right (quid juris) from the question
of fact (quid facti); and they demand that both be proved. 
Proof of the former, which has to state the right or the legal
claim, they entitle the deduction. Many empirical concepts are
employed without question from anyone. Since experience is
always available for the proof of their objective reality, we be-
lieve ourselves, even without a deduction, to be justified in ap-
propriating to them a meaning, an ascribed significance. But
there are also usurpatory concepts, such as fortune, fate,
which, though allowed to circulate by almost universal indul-
gence, are yet from time to time challenged by the question:
quid juris. This demand for a deduction involves us in con-
siderable perplexity, no clear legal title, sufficient to justify
their employment, being obtainable either from experience or
from reason. 
Now among the manifold concepts which form the highly
P 121
complicated web of human knowledge, there are some which
are marked out for pure a priori employment, in complete in-
dependence of all experience; and their right to be so em-
ployed always demands a deduction. For since empirical proofs
do not suffice to justify this kind of employment, we are faced
by the problem how these concepts can relate to objects which
they yet do not obtain from any experience. The explanation
of the manner in which concepts can thus relate a priori to
objects I entitle their transcendental deduction; and from it I
distinguish empirical deduction, which shows the manner in
which a concept is acquired through experience and through
reflection upon experience, and which therefore concerns, not
its legitimacy, but only its de facto mode of origination. 
We are already in possession of concepts which are of two
quite different kinds, and which yet agree in that they relate
to objects in a completely a priori manner, namely, the con-
cepts of space and time as forms of sensibility, and the cate-
gories as concepts of understanding. To seek an empirical de-
duction of either of these types of concept would be labour
entirely lost. For their distinguishing feature consists just in
this, that they relate to their objects without having borrowed
from experience anything that can serve in the representation
of these objects. If, therefore, a deduction of such concepts is
indispensable, it must in any case be transcendental. 
We can, however, with regard to these concepts, as with
regard to all knowledge, seek to discover in experience, if
not the principle of their possibility, at least the occasioning
causes of their production. The impressions of the senses
supplying the first stimulus, the whole faculty of knowledge
opens out to them, and experience is brought into exist-
ence. That experience contains two very dissimilar elements,
namely, the matter of knowledge [obtained] from the senses,
and a certain form for the ordering of this matter, [obtained]
from the inner source of the pure intuition and thought
which, on occasion of the sense-impressions, are first brought
into action and yield concepts. Such an investigation of the
first strivings of our faculty of knowledge, whereby it advances
from particular perceptions to universal concepts, is un-
doubtedly of great service. We are indebted to the celebrated
P 122
Locke for opening out this new line of enquiry. But a deduc-
tion of the pure a priori concepts can never be obtained in
this manner; it is not to be looked for in any such direction. 
For in view of their subsequent employment, which has to be
entirely independent of experience, they must be in a position
to show a certificate of birth quite other than that of descent
from experiences. Since this attempted physiological deriva-
tion concerns a quaestio facti, it cannot strictly be called
deduction; and I shall therefore entitle it the explanation of
the possession of pure knowledge. Plainly the only deduction
that can be given of this knowledge is one that is transcen-
dental, not empirical. In respect to pure a priori concepts
the latter type of deduction is an utterly useless enterprise
which can be engaged in only by those who have failed to
grasp the quite peculiar nature of these modes of know-
But although it may be admitted that the only kind of
deduction of pure a priori knowledge which is possible is on
transcendental lines, it is not at once obvious that a deduc-
tion is indispensably necessary. We have already, by means of
a transcendental deduction, traced the concepts of space and
time to their sources, and have explained and determined
their a priori objective validity. Geometry, however, proceeds
with security in knowledge that is completely a priori, and has
no need to beseech philosophy for any certificate of the pure
and legitimate descent of its fundamental concept of space. 
But the concept is employed in this science only in its reference
to the outer sensible world -- of the intuition of which space
is the pure form -- where all geometrical knowledge, grounded
as it is in a priori intuition, possesses immediate evidence. 
The objects, so far as their form is concerned, are given,
through the very knowledge of them, a priori in intuition. 
otherwise; it is with them that the unavoidable demand for a
transcendental deduction, not only of themselves, but also
of the concept of space, first originates. For since they speak
of objects through predicates not of intuition and sensibility
but of pure a priori thought, they relate to objects universally,
P 123
that is, apart from all conditions of sensibility. Also, not being
grounded in experience, they cannot, in a priori intuition,
exhibit any object such as might, prior to all experience,
serve as ground for their synthesis. For these reasons, they
arouse suspicion not merely in regard to the objective
validity and the limits of their own employment, but owing
to their tendency to employ the concept of space beyond the
conditions of sensible intuition, that concept also they render
ambiguous; and this, indeed, is why we have already found
a transcendental deduction of it necessary. The reader must
therefore be convinced of the unavoidable necessity of such
a transcendental deduction before he has taken a single step
in the field of pure reason. Otherwise he proceeds blindly,
and after manifold wanderings must come back to the same
ignorance from which he started. At the same time, if he is
not to lament over obscurity in matters which are by their
very nature deeply veiled, or to be too easily discouraged in
the removal of obstacles, he must have a clear foreknowledge
of the inevitable difficulty of the undertaking. For we must
either completely surrender all claims to make judgments of
pure reason in the most highly esteemed of all fields, that
which transcends the limits of all possible experience, or else
bring this critical enquiry to completion. 
We have already been able with but little difficulty to
explain how the concepts of space and time, although a priori
modes of knowledge, must necessarily relate to objects, and
how independently of all experience they make possible a
synthetic knowledge of objects. For since only by means of
such pure forms of sensibility can an object appear to us,
and so be an object of empirical intuition, space and time
are pure intuitions which contain a priori the condition of the
possibility of objects as appearances, and the synthesis which
takes place in them has objective validity. 
The categories of understanding, on the other hand, do
not represent the conditions under which objects are given
in intuition. Objects may, therefore, appear to us without
P 124
their being under the necessity of being related to the functions
of understanding; and understanding need not, therefore,
contain their a priori conditions. Thus a difficulty such as
we did not meet with in the field of sensibility is here
presented, namely, how subjective conditions of thought can
have objective validity, that is, can furnish conditions of the
possibility of all knowledge of objects. For appearances can
certainly be given in intuition independently of functions of
the understanding. Let us take, for instance, the concept of
cause, which signifies a special kind of synthesis, whereby
upon something, A, there is posited something quite different,
B, according to a rule. It is not manifest a priori why appear-
ances should contain anything of this kind (experiences
cannot be cited in its proof, for what has to be established
is the objective validity of a concept that is a priori); and it
is therefore a priori doubtful whether such a concept be
not perhaps altogether empty, and have no object anywhere
among appearances. That objects of sensible intuition must
conform to the formal conditions of sensibility which lie
a priori in the mind is evident, because otherwise they would
not be objects for us. But that they must likewise conform
to the conditions which the understanding requires for the
synthetic unity of thought, is a conclusion the grounds of
which are by no means so obvious. Appearances might very
well be so constituted that the understanding should not find
them to be in accordance with the Conditions of its unity. 
Everything might be in such confusion that, for instance,
in the series of appearances nothing presented itself which
might yield a rule of synthesis and so answer to the concept
of cause and effect. This concept would then be altogether
empty, null, and meaningless. But since intuition stands in
no need whatsoever of the functions of thought, appearances
would none the less present objects to our intuition. 
If we thought to escape these toilsome enquiries by saying
that experience continually presents examples of such regu-
larity among appearances and so affords abundant oppor-
tunity of abstracting the concept of cause, and at the same
time of verifying the objective validity of such a concept, we
should be overlooking the fact that the concept of cause can
P 125
never arise in this manner. It must either be grounded com-
pletely a priori in the understanding, or must be entirely given
up as a mere phantom of the brain. For this concept makes
strict demand that something, A, should be such that some-
thing else, B, follows from it necessarily and in accordance
with an absolutely universal rule. Appearances do indeed pre-
sent cases from which a rule can be obtained according to
which something usually happens, but they never prove the
sequence to be necessary. To the synthesis of cause and
effect there belongs a dignity which cannot be empirically
expressed, namely that the effect not only succeeds upon the
cause, but that it is posited through it and arises out of it. 
This strict universality of the rule is never a characteristic of
empirical rules; they can acquire through induction only com-
parative universality, that is, extensive applicability. If we
were to treat pure concepts of understanding as merely em-
pirical products, we should be making a complete change in
[the manner of] their employment. 
Transition to the Transcendental Deduction of the
There are only two possible ways in which synthetic re-
presentations and their objects can establish connection,
obtain necessary relation to one another, and, as it were, meet
one another. Either the object alone must make the repre-
sentation possible, or the representation alone must make the
object possible. In the former case, this relation is only em-
pirical, and the representation is never possible a priori. This
is true of appearances, as regards that [element] in them
which belongs to sensation. In the latter case, representation
in itself does not produce its object in so far as existence is
concerned, for we are not here speaking of its causality by
means of the will. None the less the representation is a priori
determinant of the object, if it be the case that only through
P 126
the representation is it possible to know anything as an object. 
Now there are two conditions under which alone the know-
ledge of an object is possible, first, intuition, through which
it is given, though only as appearance; secondly, concept,
through which an object is thought corresponding to this in-
tuition. It is evident from the above that the first condition,
namely, that under which alone objects can be intuited, does
actually lie a priori in the mind as the formal ground of the
objects. All appearances necessarily agree with this formal
condition of sensibility, since only through it can they appear,
that is, be empirically intuited and given. The question now
arises whether a priori concepts do not also serve as ante-
cedent conditions under which alone anything can be, if not
intuited, yet thought as object in general. In that case all em-
pirical knowledge of objects would necessarily conform to such
concepts, because only as thus presupposing them is anything
possible as object of experience. Now all experience does indeed
contain, in addition to the intuition of the senses through
which something is given, a concept of an object as being
thereby given, that is to say, as appearing. Concepts of objects
in general thus underlie all empirical knowledge as its a priori
conditions. The objective validity of the categories as a priori
concepts rests, therefore, on the fact that, so far as the form
of thought is concerned, through them alone does experience
become possible. They relate of necessity and a priori to
objects of experience, for the reason that only by means of
them can any object whatsoever of experience be thought. 
 The transcendental deduction of all a priori concepts has
thus a principle according to which the whole enquiry must
be directed, namely, that they must be recognised as a priori
conditions of the possibility of experience, whether of the
intuition which is to be met with in it or of the thought. Con-
cepts which yield the objective ground of the possibility of
experience are for this very reason necessary. But the unfold-
ing of the experience wherein they are encountered is not
their deduction; it is only their illustration. For on any such
P 127
exposition they would be merely accidental. Save through
their original relation to possible experience, in which all
objects of knowledge are found, their relation to any one
object would be quite incomprehensible. 
 The illustrious Locke, failing to take account of these con-
siderations, and meeting with pure concepts of the understand-
ing in experience, deduced them also from experience, and
yet proceeded so inconsequently that he attempted with their
aid to obtain knowledge which far transcends all limits of ex-
perience. David Hume recognised that, in order to be able to
do this, it was necessary that these concepts should have an
a priori origin. But since he could not explain how it can be
possible that the understanding must think concepts, which
are not in themselves connected in the understanding, as being
necessarily connected in the object, and since it never occurred
to him that the understanding might itself, perhaps, through
these concepts, be the author of the experience in which its
objects are found, he was constrained to derive them from
experience, namely, from a subjective necessity (that is, from
custom), which arises from repeated association in experience,
and which comes mistakenly to be regarded as objective. But
from these premisses he argued quite consistently. It is im-
possible, he declared, with these concepts and the principles to
which they give rise, to pass beyond the limits of experience. 
 *There are three original sources (capacities or faculties of
the soul) which contain the conditions of the possibility of all
experience, and cannot themselves be derived from any other
faculty of the mind, namely, sense, imagination, and appercep-
tion. Upon them are grounded (1) the synopsis of the manifold
a priori through sense; (2) the synthesis of this manifold
through imagination; finally (3) the unity of this synthesis
through original apperception. All these faculties have a
transcendental (as well as an empirical) employment which
concerns the form alone, and is possible a priori. As regards
sense, we have treated of this above in the first part; we shall
now endeavour to comprehend the nature of the other two. 
P 128
Now this empirical derivation, in which both philosophers
agree, cannot be reconciled with the scientific a priori know-
ledge which we do actually possess, namely, pure mathematics
and general science of nature; and this fact therefore suffices
to disprove such derivation. 
While the former of these two illustrious men opened a wide
door to enthusiasm -- for if reason once be allowed such rights,
it will no longer allow itself to be kept within bounds by
vaguely defined recommendations of moderation -- the other
gave himself over entirely to scepticism, having, as he believed,
discovered that what had hitherto been regarded as reason
was but an all-prevalent illusion infecting our faculty of know-
ledge. We now propose to make trial whether it be not possible
to find for human reason safe conduct between these two rocks,
assigning to her determinate limits, and yet keeping open for
her the whole field of her appropriate activities. 
But first I shall introduce a word of explanation in regard
to the categories. They are concepts of an object in general, by
means of which the intuition of an object is regarded as deter-
mined in respect of one of the logical functions of judgment. 
Thus the function of the categorical judgment is that of the
relation of subject to predicate; for example, 'All bodies are
divisible'. But as regards the merely logical employment of
the understanding, it remains undetermined to which of the
two concepts the function of the subject, and to which the
function of predicate, is to be assigned. For we can also say,
'Something divisible is a body'. But when the concept of body
is brought under the category of substance, it is thereby de-
termined that its empirical intuition in experience must always
be considered as subject and never as mere predicate. Simi-
larly with all the other categories. 
P 129
Section 2
THAT a concept, although itself neither contained in the con-
cept of possible experience nor consisting of elements of a
possible experience, should be produced completely a priori
and should relate to an object, is altogether contradictory and
impossible. For it would then have no content, since no intui-
tion corresponds to it; and intuitions in general, through which
objects can be given to us, constitute the field, the whole ob-
ject, of possible experience. An a priori concept which did
not relate to experience would be only the logical form of a
concept, not the concept itself through which something is
Pure a priori concepts, if such exist, cannot indeed con-
tain anything empirical; yet, none the less, they can serve
solely as a priori conditions of a possible experience. Upon
this ground alone can their objective reality rest. 
If, therefore, we seek to discover how pure concepts of
understanding are possible, we must enquire what are the
a priori conditions upon which the possibility of experience
rests, and which remain as its underlying grounds when every-
thing empirical is abstracted from appearances. A concept
which universally and adequately expresses such a normal and
P 130
objective condition of experience would be entitled a pure con-
cept of understanding. Certainly, once I am in possession of
pure concepts of understanding, I can think objects which may
be impossible, or which, though perhaps in themselves possible,
cannot be given in any experience. For in the connecting of
these concepts something may be omitted which yet neces-
sarily belongs to the condition of a possible experience (as in
the concept of a spirit). Or, it may be, pure concepts are ex-
tended further than experience can follow (as with the concept
of God). But the elements of all modes of a priori knowledge,
even of capricious and incongruous fictions, though they
cannot, indeed, be derived from experience, since in that case
they would not be knowledge a priori, must none the less
always contain the pure a priori conditions of a possible ex-
perience and of an empirical object. Otherwise nothing would
be thought through them, and they themselves, being without
data, could never arise even in thought. 
The concepts which thus contain a priori the pure thought
involved in every experience, we find in the categories. If we
can prove that by their means alone an object can be thought,
this will be a sufficient deduction of them, and will justify their
objective validity. But since in such a thought more than simply
the faculty of thought, the understanding, is brought into play,
and since this faculty itself, as a faculty of knowledge that is
meant to relate to objects, calls for explanation in regard to the
possibility of such relation, we must first of all consider, not in
their empirical but in their transcendental constitution, the
subjective sources which form the a priori foundation of the
possibility of experience. 
If each representation were completely foreign to every
other, standing apart in isolation, no such thing as knowledge
would ever arise. For knowledge is [essentially] a whole in
which representations stand compared and connected. As sense
contains a manifold in its intuition, I ascribe to it a synopsis. 
But to such synopsis a synthesis must always correspond; re-
ceptivity can make knowledge possible only when combined
with spontaneity. Now this spontaneity is the ground of a
threefold synthesis which must necessarily be found in all
knowledge; namely, the apprehension of representations as
modifications of the mind in intuition, their reproduction in
P 131
imagination, and their recognition in a concept. These point
to three subjective sources of knowledge which make possible
the understanding itself -- and consequently all experience as
its empirical product. 
Preliminary Remark 
The deduction of the categories is a matter of such ex-
treme difficulty, compelling us to penetrate so deeply into the
first grounds of the possibility of our knowledge in general,
that in order to avoid the elaborateness of a complete theory,
and yet at the same time to omit nothing in so indispensable
an enquiry, I have found it advisable in the four following pass-
ages rather to prepare than to instruct the reader. System-
atic exposition of these elements of the understanding is first
given in Section 3, immediately following. The reader must
not therefore be deterred by obscurities in these earlier sections. 
They are unavoidable in an enterprise never before attempted. 
They will, as I trust, in the section referred to, finally give way
to complete insight. 
1. The Synthesis of Apprehension in Intuition 
Whatever the origin of our representations, whether they
are due to the influence of outer things, or are produced
through inner causes, whether they arise a priori, or being
appearances have an empirical origin, they must all, as modi-
fications of the mind, belong to inner sense. All our know-
ledge is thus finally subject to time, the formal condition of
inner sense. In it they must all be ordered, connected, and
brought into relation. This is a general observation which,
throughout what follows, must be borne in mind as being
quite fundamental. 
Every intuition contains in itself a manifold which can
be represented as a manifold only in so far as the mind distin-
guishes the time in the sequence of one impression upon another;
for each representation, in so far as it is contained in a single
moment, can never be anything but absolute unity. In order
that unity of intuition may arise out of this manifold (as is
required in the representation of space) it must first be run
through, and held together. This act I name the synthesis of
apprehension, because it is directed immediately upon intuition,
which does indeed offer a manifold, but a manifold which can
P 132
never be represented as a manifold, and as contained in a
single representation, save in virtue of such a synthesis. 
This synthesis of apprehension must also be exercised
a priori, that is, in respect of representations which are not
empirical. For without it we should never have a priori the
representations either of space or of time. They can be pro-
duced only through the synthesis of the manifold which sen-
sibility presents in its original receptivity. We have thus a pure
synthesis of apprehension. 
2. The Synthesis of Reproduction in Imagination 
It is a merely empirical law, that representations which
have often followed or accompanied one another finally be-
come associated, and so are set in a relation whereby, even in
the absence of the object, one of these representations can, in
accordance with a fixed rule, bring about a transition of the
mind to the other. But this law of reproduction presupposes
that appearances are themselves actually subject to such a
rule, and that in the manifold of these representations a co-
existence or sequence takes place in conformity with certain
rules. Otherwise our empirical imagination would never find
opportunity for exercise appropriate to its powers, and so
would remain concealed within the mind as a dead and to us
unknown faculty. If cinnabar were sometimes red, sometimes
black, sometimes light, sometimes heavy, if a man changed
sometimes into this and sometimes into that animal form, if
the country on the longest day were sometimes covered with
fruit, sometimes with ice and snow, my empirical imagina-
tion would never find opportunity when representing red
colour to bring to mind heavy cinnabar. Nor could there be
an empirical synthesis of reproduction, if a certain name were
sometimes given to this, sometimes to that object, or were one
and the same thing named sometimes in one way, sometimes
in another, independently of any rule to which appearances
are in themselves subject. 
There must then be something which, as the a priori
ground of a necessary synthetic unity of appearances, makes
their reproduction possible. What that something is we
P 133
soon discover, when we reflect that appearances are not
things in themselves, but are the mere play of our representa-
tions, and in the end reduce to determinations of inner sense. 
For if we can show that even our purest a priori intuitions
yield no knowledge, save in so far as they contain a com-
bination of the manifold such as renders a thoroughgoing
synthesis of reproduction possible, then this synthesis of im-
agination is likewise grounded, antecedently to all experi-
ence, upon a priori principles; and we must assume a pure
transcendental synthesis of imagination as conditioning the
very possibility of all experience. For experience as such neces-
sarily presupposes the reproducibility of appearances. When
I seek to draw a line in thought, or to think of the time from
one noon to another, or even to represent to myself some par-
ticular number, obviously the various manifold representa-
tions that are involved must be apprehended by me in thought
one after the other. But if I were always to drop out of thought
the preceding representations (the first parts of the line, the
antecedent parts of the time period, or the units in the order
represented), and did not reproduce them while advancing to
those that follow, a complete representation would never be
obtained: none of the above-mentioned thoughts, not even the
purest and most elementary representations of space and time,
could arise. 
The synthesis of apprehension is thus inseparably bound
up with the synthesis of reproduction. And as the former con-
stitutes the transcendental ground of the possibility of all
modes of knowledge whatsoever -- of those that are pure
a priori no less than of those that are empirical -- the repro-
ductive synthesis of the imagination is to be counted among
the transcendental acts of the mind. We shall therefore entitle
this faculty the transcendental faculty of imagination. 
3. The Synthesis of Recognition in a Concept 
If we were not conscious that what we think is the same
as what we thought a moment before, all reproduction in the
series of representations would be useless. For it would in its
present state be a new representation which would not in any
way belong to the act whereby it was to be gradually gener-
P 134
ated. The manifold of the representation would never, there-
fore, form a whole, since it would lack that unity which only
consciousness can impart to it. If, in counting, I forget that
the units, which now hover before me, have been added to
one another in succession, I should never know that a total
is being produced through this successive addition of unit to
unit, and so would remain ignorant of the number. For the
concept of the number is nothing but the consciousness of
this unity of synthesis. 
The word 'concept' might of itself suggest this remark. 
For this unitary consciousness is what combines the mani-
fold, successively intuited, and thereupon also reproduced,
into one representation. This consciousness may often be only
faint, so that we do not connect it with the act itself, that
is, not in any direct manner with the generation of the repre-
sentation, but only with the outcome [that which is thereby
represented]. But notwithstanding these variations, such con-
sciousness, however indistinct, must always be present; with-
out it, concepts, and therewith knowledge of objects, are
altogether impossible. 
At this point we must make clear to ourselves what we
mean by the expression 'an object of representations'. We
have stated above that appearances are themselves nothing
but sensible representations, which, as such and in themselves,
must not be taken as objects capable of existing outside our
power of representation. What, then, is to be understood when
we speak of an object corresponding to, and consequently
also distinct from, our knowledge? It is easily seen that this
object must be thought only as something in general = x, since
outside our knowledge we have nothing which we could set
over against this knowledge as corresponding to it. 
Now we find that our thought of the relation of all know-
ledge to its object carries with it an element of necessity; the
object is viewed as that which prevents our modes of know-
ledge from being haphazard or arbitrary, and which deter-
mines them a priori in some definite fashion. For in so far
as they are to relate to an object, they must necessarily agree
P 135
with one another, that is, must possess that unity which con-
stitutes the concept of an object. 
But it is clear that, since we have to deal only with the
manifold of our representations, and since that x (the object)
which corresponds to them is nothing to us -- being, as it is,
something that has to be distinct from all our representations
-- the unity which the object makes necessary can be nothing
else than the formal unity of consciousness in the synthesis of
the manifold of representations. It is only when we have thus
produced synthetic unity in the manifold of intuition that we
are in a position to say that we know the object. But this unity
is impossible if the intuition cannot be generated in accord-
ance with a rule by means of such a function of synthesis as
makes the reproduction of the manifold a priori necessary,
and renders possible a concept in which it is united. Thus we
think a triangle as an object, in that we are conscious of the
combination of three straight lines according to a rule by
which such an intuition can always be represented. This unity
of rule determines all the manifold, and limits it to conditions
which make unity of apperception possible. The concept of
this unity is the representation of the object = x, which I
think through the predicates, above mentioned, of a triangle. 
All knowledge demands a concept, though that concept
may, indeed, be quite imperfect or obscure. But a concept
is always, as regards its form, something universal which
serves as a rule. The concept of body, for instance, as the
unity of the manifold which is thought through it, serves as
a rule in our knowledge of outer appearances. But it can be
a rule for intuitions only in so far as it represents in any given
appearances the necessary reproduction of their manifold,
and thereby the synthetic unity in our consciousness of them. 
The concept of body, in the perception of something outside
us, necessitates the representation of extension, and there-
with representations of impenetrability, shape, etc. 
All necessity, without exception, is grounded in a tran-
scendental condition. There must, therefore, be a transcend-
ental ground of the unity of consciousness in the synthesis
of the manifold of all our intuitions, and consequently also
of the concepts of objects in general, and so of all objects
of experience, a ground without which it would be impossible
P 136
to think any object for our intuitions; for this object is no
more than that something, the concept of which expresses
such a necessity of synthesis. 
This original and transcendental condition is no other
than transcendental apperception. Consciousness of self
according to the determinations of our state in inner percep-
tion is merely empirical, and always changing. No fixed
and abiding self can present itself in this flux of inner appear-
ances. Such consciousness is usually named inner sense, or
empirical apperception. What has necessarily to be repre-
sented as numerically identical cannot be thought as such
through empirical data. To render such a transcendental
presupposition valid, there must be a condition which
precedes all experience, and which makes experience itself
There can be in us no modes of knowledge, no connection
or unity of one mode of knowledge with another, without that
unity of consciousness which precedes all data of intuitions,
and by relation to which representation of objects is alone
possible. This pure original unchangeable consciousness I
shall name transcendental apperception. That it deserves this
name is clear from the fact that even the purest objective
unity, namely, that of the a priori concepts (space and time),
is only possible through relation of the intuitions to such
unity of consciousness. The numerical unity of this appercep-
tion is thus the a priori ground of all concepts, just as the
manifoldness of space and time is the a priori ground of
the intuitions of sensibility. 
 This transcendental unity of apperception forms out of
all possible appearances, which can stand alongside one
another in one experience, a connection of all these repre-
sentations according to laws. For this unity of consciousness
would be impossible if the mind in knowledge of the manifold
could not become conscious of the identity of function whereby
it synthetically combines it in one knowledge. The original
and necessary consciousness of the identity of the self is thus
at the same time a consciousness of an equally necessary unity
of the synthesis of all appearances according to concepts, that
P 137
is, according to rules, which not only make them necessarily
reproducible but also in so doing determine an object for their
intuition, that is, the concept of something wherein they are
necessarily interconnected. For the mind could never think
its identity in the manifoldness of its representations, and
indeed think this identity a priori, if it did not have before
its eyes the identity of its act, whereby it subordinates all
synthesis of apprehension (which is empirical) to a transcend-
ental unity, thereby rendering possible their interconnection
according to a priori rules. 
Now, also, we are in a position to determine more ade-
quately our concept of an object in general. All representations
have, as representations, their object, and can themselves in
turn become objects of other representations. Appearances are
the sole objects which can be given to us immediately, and
that in them which relates immediately to the object is called
intuition. But these appearances are not things in themselves;
they are only representations, which in turn have their object
-- an object which cannot itself be intuited by us, and which
may, therefore, be named the non-empirical, that is, transcend-
ental object = x. 
The pure concept of this transcendental object, which in
reality throughout all our knowledge is always one and the
same, is what can alone confer upon all our empirical con-
cepts in general relation to an object, that is, objective reality. 
This concept cannot contain any determinate intuition, and
therefore refers only to that unity which must be met with
in any manifold of knowledge which stands in relation to an
object. This relation is nothing but the necessary unity of
consciousness, and therefore also of the synthesis of the mani-
fold, through a common function of the mind, which com-
bines it in one representation. Since this unity must be re-
garded as necessary a priori -- otherwise knowledge would
be without an object -- the relation to a transcendental object,
that is, the objective reality of our empirical knowledge, rests
on the transcendental law, that all appearances, in so far as
through them objects are to be given to us, must stand under
those a priori rules of synthetical unity whereby the inter-
P 138
relating of these appearances in empirical intuition is alone
possible. In other words, appearances in experience must
stand under the conditions of the necessary unity of apper-
ception, just as in mere intuition they must be subject to the
formal conditions of space and of time. Only thus can any
knowledge become possible at all. 
4.Preliminary Explanation of the Possibility of the
Categories, as Knowledge a priori 
There is one single experience in which all perceptions
are represented as in thoroughgoing and orderly connection,
just as there is only one space and one time in which all
modes of appearance and all relation of being or not being
occur. When we speak of different experiences, we can refer
only to the various perceptions, all of which, as such, belong
to one and the same general experience. This thoroughgoing
synthetic unity of perceptions is indeed the form of experience;
it is nothing else than the synthetic unity of appearances in
accordance with concepts. 
 Unity of synthesis according to empirical concepts would
be altogether accidental, if these latter were not based on a
transcendental ground of unity. Otherwise it would be possible
for appearances to crowd in upon the soul, and yet to be such
as would never allow of experience. Since connection in accord-
ance with universal and necessary laws would be lacking, all
relation of knowledge to objects would fall away. The appear-
ances might, indeed, constitute intuition without thought,
but not knowledge; and consequently would be for us as good
as nothing. 
The a priori conditions of a possible experience in general
are at the same time conditions of the possibility of objects
of experience. Now I maintain that the categories, above
cited, are nothing but the conditions of thought in a possible
experience, just as space and time are the conditions of in-
tuition for that same experience. They are fundamental con-
cepts by which we think objects in general for appearances,
and have therefore a priori objective validity. This is exactly
what we desired to prove. 
P 139
But the possibility, indeed the necessity, of these cate-
gories rests on the relation in which our entire sensibility,
and with it all possible appearances, stand to original apper-
ception. In original apperception everything must necessarily
conform to the conditions of the thoroughgoing unity of self-
consciousness, that is, to the universal functions of synthesis,
namely, of that synthesis according to concepts in which
alone apperception can demonstrate a priori its complete and
necessary identity. Thus the concept of a cause is nothing but
a synthesis (of that which follows in the time-series, with other
appearances) according to concepts; and without such unity,
which has its a priori rule, and which subjects the appear-
ances to itself, no thoroughgoing, universal, and therefore
necessary, unity of consciousness would be met with in the
manifold of perceptions. These perceptions would not then
belong to any experience, consequently would be without an
object, merely a blind play of representations, less even than
a dream. 
All attempts to derive these pure concepts of understand-
ing from experience, and so to ascribe to them a merely em-
pirical origin, are entirely vain and useless. I need not insist
upon the fact that, for instance, the concept of a cause involves
the character of necessity, which no experience can yield. 
Experience does indeed show that one appearance customarily
follows upon another, but not that this sequence is necessary,
nor that we can argue a priori and with complete universality
from the antecedent, viewed as a condition, to the consequent. 
But as regards the empirical rule of association, which we
must postulate throughout when we assert that everything in
the series of events is so subject to rule that nothing ever
happens save in so far as something precedes it on which it
universally follows -- upon what I ask, does this rule, as a law
of nature, rest? How is this association itself possible? The
ground of the possibility of the association of the manifold, so
far as it lies in the object, is named the affinity of the manifold. 
I therefore ask, how are we to make comprehensible to our-
selves the thoroughgoing affinity of appearances, whereby
they stand and must stand under unchanging laws? 
On my principles it is easily explicable. All possible ap-
pearances, as representations, belong to the totality of a pos-
P 140
sible self-consciousness. But as self-consciousness is a tran-
scendental representation, numerical identity is inseparable
from it, and is a priori certain. For nothing can come to our
knowledge save in terms of this original apperception. Now,
since this identity must necessarily enter into the synthesis of
all the manifold of appearances, so far as the synthesis is to
yield empirical knowledge, the appearances are subject to
a priori conditions, with which the synthesis of their apprehen-
sion must be in complete accordance. The representation of
a universal condition according to which a certain manifold
can be posited in uniform fashion is called a rule, and, when
it must be so posited, a law. Thus all appearances stand in
thoroughgoing connection according to necessary laws, and
therefore in a transcendental affinity, of which the empirical
is a mere consequence. 
That nature should direct itself according to our sub-
jective ground of apperception, and should indeed depend
upon it in respect of its conformity to law, sounds very strange
and absurd. But when we consider that this nature is not a
thing in itself but is merely an aggregate of appearances, so
many representations of the mind, we shall not be surprised
that we can discover it only in the radical faculty of all our
knowledge, namely, in transcendental apperception, in that
unity on account of which alone it can be entitled object of all
possible experience, that is, nature. Nor shall we be surprised
that just for this very reason this unity can be known a priori,
and therefore as necessary. Were the unity given in itself in-
dependently of the first sources of our thought, this would
never be possible. We should not then know of any source
from which we could obtain the synthetic propositions assert-
ing such a universal unity of nature. For they would then have
to be derived from the objects of nature themselves; and as this
could take place only empirically, none but a merely accidental
unity could be obtained, which would fall far short of the
necessary interconnection that we have in mind when we speak
of nature. 
P 141
Section 3
What we have expounded separately and singly in the
preceding section, we shall now present in systematic inter-
connection. There are three subjective sources of knowledge
upon which rests the possibility of experience in general and
of knowledge of its objects -- sense, imagination, and appercep-
tion. Each of these can be viewed as empirical, namely, in its
application to given appearances. But all of them are likewise
a priori elements or foundations, which make this empirical
employment itself possible. Sense represents appearances em-
pirically in perception, imagination in association (and repro-
duction), apperception in the empirical consciousness of the
identity of the reproduced representations with the appear-
ances whereby they were given, that is, in recognition. 
But all perceptions are grounded a priori in pure intuition
(in time, the form of their inner intuition as representations),
association in pure synthesis of imagination, and empirical
consciousness in pure apperception, that is, in the thorough-
going identity of the self in all possible representations. 
If, now, we desire to follow up the inner ground of this
connection of the representations to the point upon which
they have all to converge in order that they may therein for
the first time acquire the unity of knowledge necessary for
a possible experience, we must begin with pure appercep-
tion. Intuitions are nothing to us, and do not in the least
concern us if they cannot be taken up into consciousness, in
which they may participate either directly or indirectly. In
this way alone is any knowledge possible. We are conscious
a priori of the complete identity of the self in respect of all
representations which can even belong to our knowledge, as
being a necessary condition of the possibility of all representa-
P 142
tions. For in me they can represent something only in so far
as they belong with all others to one consciousness, and
therefore must be at least capable of being so connected. 
This principle holds a priori, and may be called the tran-
scendental principle of the unity of all that is manifold in our
representations, and consequently also in intuition. Since this
unity of the manifold in one subject is synthetic, pure apper-
ception supplies a principle of the synthetic unity of the mani-
fold in all possible intuition. 
 This synthetic unity presupposes or includes a synthesis,
and if the former is to be a priori necessary, the synthesis must
also be a priori. The transcendental unity of apperception thus
relates to the pure synthesis of imagination, as an a priori
condition of the possibility of all combination of the manifold
in one knowledge. 
 This proposition is of great importance and calls for careful
consideration. All representations have a necessary relation to a
possible empirical consciousness. For if they did not have this, and
if it were altogether impossible to become conscious of them, this
would practically amount to the admission of their non-existence. 
But all empirical consciousness has a necessary relation to a tran-
scendental consciousness which precedes all special experience,
namely, the consciousness of myself as original apperception. It is
therefore absolutely necessary that in my knowledge all conscious-
ness should belong to a single consciousness, that of myself. Here,
then, is a synthetic unity of the manifold (of consciousness), which
is known a priori, and so yields the ground for synthetic a priori
propositions which concern pure thought, just as do space and time
for the propositions which refer to the form of pure intuition. The
synthetic proposition, that all the variety of empirical consciousness
must be combined in one single self-consciousness, is the abso-
lutely first and synthetic principle of our thought in general. But
it must not be forgotten that the bare representation 'I' in relation
to all other representations (the collective unity of which it makes
possible) is transcendental consciousness. Whether this representa-
tion is clear (empirical consciousness) or obscure, or even whether
it ever actually occurs, does not here concern us. But the possibility
of the logical form of all knowledge is necessarily conditioned by
relation to this apperception as a faculty. 
P 142
But only the productive synthesis of the
P 143
imagination can take place a priori; the reproductive rests
upon empirical conditions. Thus the principle of the necessary
unity of pure (productive) synthesis of imagination, prior to
apperception, is the ground of the possibility of all know-
ledge, especially of experience. 
We entitle the synthesis of the manifold in imagination
transcendental, if without distinction of intuitions it is directed
exclusively to the a priori combination of the manifold; and
the unity of this synthesis is called transcendental, if it is repre-
sented as a priori necessary in relation to the original unity
of apperception. Since this unity of apperception underlies
the possibility of all knowledge, the transcendental unity of
the synthesis of imagination is the pure form of all possible
knowledge; and by means of it all objects of possible experi-
ence must be represented a priori. 
The unity of apperception in relation to the synthesis of
imagination is the understanding; and this same unity, with
reference to the transcendental synthesis of the imagination,
the pure understanding. In the understanding there are then
pure a priori modes of knowledge which contain the neces-
sary unity of the pure synthesis of imagination in respect of all
possible appearances. These are the categories, that is, the pure
concepts of understanding. The empirical faculty of know-
ledge in man must therefore contain an understanding which
relates to all objects of the senses, although only by means of
intuition and of its synthesis through imagination. All appear-
ances, as data for a possible experience, are subject to this
understanding. This relation of appearances to possible ex-
perience is indeed necessary, for otherwise they would yield
no knowledge and would not in any way concern us. We have,
therefore, to recognise that pure understanding, by means of
the categories, is a formal and synthetic principle of all ex-
periences, and that appearances have a necessary relation to
the understanding. 
We will now, starting from below, namely, with the em-
pirical, strive to make clear the necessary connection in which
understanding, by means of the categories, stands to appear-
ances. What is first given to us is appearance. When combined
with consciousness, it is called perception. (Save through its
P 144
relation to a consciousness that is at least possible, appear-
ance could never be for us an object of knowledge, and so
would be nothing to us; and since it has in itself no objective
reality, but exists only in being known, it would be nothing
at all. ) Now, since every appearance contains a manifold,
and since different perceptions therefore occur in the mind
separately and singly, a combination of them, such as they
cannot have in sense itself, is demanded. There must therefore
exist in us an active faculty for the synthesis of this manifold. 
To this faculty I give the title, imagination. Its action, when
immediately directed upon perceptions, I entitle apprehen-
sion. Since imagination has to bring the manifold of intuition
into the form of an image, it must previously have taken the
impressions up into its activity, that is, have apprehended them. 
 But it is clear that even this apprehension of the manifold
would not by itself produce an image and a connection of the
impressions, were it not that there exists a subjective ground
which leads the mind to reinstate a preceding perception
alongside the subsequent perception to which it has passed,
and so to form whole series of perceptions. This is the repro-
ductive faculty of imagination, which is merely empirical. 
If, however, representations reproduced one another in any
order, just as they happened to come together, this would not
lead to any determinate connection of them, but only to acci-
dental collocations; and so would not give rise to any know-
ledge. Their reproduction must, therefore, conform to a
rule, in accordance with which a representation connects in
the imagination with some one representation in preference
to another. This subjective and empirical ground of repro-
duction according to rules is what is called the association of
 Psychologists have hitherto failed to realise that imagination
is a necessary ingredient of perception itself. This is due partly to
the fact that that faculty has been limited to reproduction, partly to
the belief that the senses not only supply impressions but also com-
bine them so as to generate images of objects. For that purpose some-
thing more than the mere receptivity of impressions is undoubtedly
required, namely, a function for the synthesis of them. 
P 144
 Now if this unity of association had not also an objective
P 145
ground which makes it impossible that appearances should
be apprehended by the imagination otherwise than under the
condition of a possible synthetic unity of this apprehension, it
would be entirely accidental that appearances should fit into a
connected whole of human knowledge. For even though we
should have the power of associating perceptions, it would
remain entirely undetermined and accidental whether they
would themselves be associable; and should they not be associ-
able, there might exist a multitude of perceptions, and indeed
an entire sensibility, in which much empirical consciousness
would arise in my mind, but in a state of separation, and without
belonging to a consciousness of myself. This, however, is im-
possible. For it is only because I ascribe all perceptions to one
consciousness (original apperception) that I can say of all per-
ceptions that I am conscious of them. There must, therefore,
be an objective ground (that is, one that can be comprehended
a priori, antecedently to all empirical laws of the imagination)
upon which rests the possibility, nay, the necessity, of a law
that extends to all appearances -- a ground, namely, which
constrains us to regard all appearances as data of the senses
that must be associable in themselves and subject to universal
rules of a thoroughgoing connection in their reproduction. 
This objective ground of all association of appearances I
entitle their affinity. It is nowhere to be found save in the
principle of the unity of apperception, in respect of all know-
ledge which is to belong to me. According to this principle all
appearances, without exception, must so enter the mind or be
apprehended, that they conform to the unity of appercep-
tion. Without synthetic unity in their connection, this would
be impossible; and such synthetic unity is itself, therefore,
objectively necessary. 
The objective unity of all empirical consciousness in one
consciousness, that of original apperception, is thus the neces-
sary condition of all possible perception; and [this being recog-
nised we can prove that] the affinity of all appearances, near or
remote, is a necessary consequence of a synthesis in imagina-
tion which is grounded a priori on rules. 
Since the imagination is itself a faculty of a priori syn-
thesis, we assign to it the title, productive imagination. In so
far as it aims at nothing but necessary unity in the synthesis of
P 146
what is manifold in appearance, it may be entitled the tran-
scendental function of imagination. That the affinity of appear-
ances, and with it their association, and through this, in turn,
their reproduction according to laws, and so [as involving
these various factors] experience itself, should only be possible
by means of this transcendental function of imagination, is
indeed strange, but is none the less an obvious consequence of
the preceding argument. For without this transcendental func-
tion no concepts would together make up a unitary
 The abiding and unchanging 'I' (pure apperception)
forms the correlate of all our representations in so far as it is
to be at all possible that we should become conscious of them. 
All consciousness as truly belongs to an all-comprehensive
pure apperception, as all sensible intuition, as representation,
does to a pure inner intuition, namely, to time. It is this
apperception which must be added to pure imagination, in
order to render its function intellectual. For since the syn-
thesis of imagination connects the manifold only as it appears
in intuition, as, for instance, in the shape of a triangle, it is,
though exercised a priori, always in itself sensible. And while
concepts, which belong to the understanding, are brought into
play through relation of the manifold to the unity of apper-
ception, it is only by means of the imagination that they can be
brought into relation to sensible intuition. 
 A pure imagination, which conditions all a priori know-
ledge, is thus one of the fundamental faculties of the human
soul. By its means we bring the manifold of intuition on the
one side, into connection with the condition of the necessary
unity of pure apperception on the other. The two extremes,
namely sensibility and understanding, must stand in neces-
sary connection with each other through the mediation of this
transcendental function of imagination, because otherwise the
former, though indeed yielding appearances, would supply no
objects of empirical knowledge, and consequently no experi-
ence. Actual experience, which is consitituted by apprehension,
association (reproduction), and finally recognition of appear-
ances, contains in recognition, the last and highest of these
P 147
merely empirical elements of experience, certain concepts
which render possible the formal unity of experience, and
therewith all objective validity (truth) of empirical knowledge. 
These grounds of the recognition of the manifold, so far as
they concern solely the form of an experience in general, are
the categories. Upon them is based not only all formal unity in
the [transcendental] synthesis of imagination, but also, thanks
to that synthesis, all its empirical employment (in recogni-
tion, reproduction, association, apprehension) in connection
with the appearances. For only by means of these funda-
mental concepts can appearances belong to knowledge or
even to our consciousness, and so to ourselves. 
 Thus the order and regularity in the appearances, which
we entitle nature, we ourselves introduce. We could never
find them in appearances, had no we ourselves, or the nature
of our mind, originally set them there. For this unity of nature
has to be a necessary one, that is, has to be an a priori certain
unity of the connection of appearances; and such synthetic
unity could not be established a priori if there were not sub-
jective grounds of such unity contained a priori in the original
cognitive powers of our mind, and if these subjective condi-
tions, inasmuch as they are the grounds of the possibility of
knowing any object whatsoever in experience, were not at
the same time objectively valid. 
 We have already defined the understanding in various
different ways: as a spontaneity of knowledge (in distinction
from the receptivity of sensibility), as a power of thought, as
a faculty of concepts, or again of judgments. All these defini-
tions, when they are adequately understood, are identical. 
We may now characterise it as the faculty of rules. This dis-
tinguishing mark is more fruitful, and approximates more
closely to its essential nature. Sensibility gives us forms (of
intuition), but understanding gives us rules. The latter is
always occupied in investigating appearances, in order to
detect some rule in them. Rules, so far as they are objective,
and therefore necessarily depend upon the knowledge of the
object, are called laws. Although we learn many laws through
P 148
experience, they are only special determinations of still higher
laws, and the highest of these, under which the others all
stand, issue a priori from the understanding itself. They are
not borrowed from experience; on the contrary, they have to
confer upon appearances their conformity to law, and so to
make experience possible. Thus the understanding is some-
thing more than a power of formulating rules through com-
parison of appearances; it is itself the lawgiver of nature. 
Save through it, nature, that is, synthetic unity of the mani-
fold of appearances according to rules, would not exist at
all (for appearances, as such, cannot exist outside us -- they
exist only in our sensibility); and this nature, as object of
knowledge in an experience, with everything which it may
contain, is only possible in the unity of apperception. The
unity of apperception is thus the transcendental ground of
the necessary conformity to law of all appearances in one ex-
perience. This same unity of apperception in respect to a
manifold of representations (determining it out of a unity)
acts as the rule, and the faculty of these rules is the under-
standing. All appearances, as possible experiences, thus lie
a priori in the understanding, and receive from it their
formal possibility, just as, in so far as they are mere in-
tuitions, they lie in the sensibility, and are, as regards their
form, only possible through it. 
However exaggerated and absurd it may sound, to say that
the understanding is itself the source of the laws of nature,
and so of its formal unity, such an assertion is none the less
correct, and is in keeping with the object to which it refers,
namely, experience. Certainly, empirical laws, as such, can
never derive their origin from pure understanding. That is
as little possible as to understand completely the inexhaust-
ible multiplicity of appearances merely by reference to the
pure form of sensible intuition. But all empirical laws are
only special determinations of the pure laws of understanding,
under which, and according to the norm of which, they first
become possible. Through them appearances take on an
orderly character, just as these same appearances, despite
P 149
the differences of their empirical form, must none the less
always be in harmony with the pure form of sensibility. 
Pure understanding is thus in the categories the law of
the synthetic unity of all appearances, and thereby first and
originally makes experience, as regards its form, possible. 
This is all that we were called upon to establish in the tran-
scendental deduction of the categories, namely, to render
comprehensible this relation of understanding to sensibility,
and, by means of sensibility, to all objects of experience. The
objective validity of the pure a priori concepts is thereby made
intelligible, and their origin and truth determined. 
Summary Representation of the Correctness of this Deduction
of the Pure Concepts of Understanding, and of its being
the only Deduction possible 
If the objects with which our knowledge has to deal were
things in themselves, we could have no a priori concepts of
them. For from what source could we obtain the concepts? If we
derived them from the object (leaving aside the question how
the object could become known to us), our concepts would
be merely empirical, not a priori. And if we derived them from
the self, that which is merely in us could not determine the
character of an object distinct from our representations, that
is, could not be a ground why a thing should exist character-
ised by that which we have in our thought, and why such a
representation should not, rather, be altogether empty. But
if, on the other hand, we have to deal only with appearances,
it is not merely possible, but necessary, that certain a priori
concepts should precede empirical knowledge of objects. 
For since a mere modification of our sensibility can never be
met with outside us, the objects, as appearances, constitute an
object which is merely in us. Now to assert in this manner,
that all these appearances, and consequently all objects with
which we can occupy ourselves, are one and all in me, that
is, are determinations of my identical self, is only another
way of saying that there must be a complete unity of them
in one and the same apperception. But this unity of possible
consciousness also constitutes the form of all knowledge of
objects; through it the manifold is thought as belonging to a
P 150
single object. Thus the mode in which the manifold of sensible
representation (intuition) belongs to one consciousness pre-
cedes all knowledge of the object as the intellectual form of
such knowledge, and itself constitutes a formal a priori know-
ledge of all objects, so far as they are thought (categories). 
The synthesis of the manifold through pure imagination,
the unity of all representations in relation to original apper-
ception, precede all empirical knowledge. Pure concepts of
understanding are thus a priori possible, and, in relation to
experience, are indeed necessary; and this for the reason
that our knowledge has to deal solely with appearances, the
possibility of which lies in ourselves, and the connection and
unity of which (in the representation of an object) are to be
met with only in ourselves. Such connection and unity must
therefore precede all experience, and are required for the
very possibility of it in its formal aspect. From this point of
view, the only feasible one, our deduction of the categories
has been developed. 
P 151
Section 2
The Possibility of Combination in General 
THE manifold of representations can be given in an intuition
which is purely sensible, that is, nothing but receptivity; and
the form of this intuition can lie a priori in our faculty of
representation, without being anything more than the mode in
which the subject is affected. But the combination (conjunctio)
of a manifold in general can never come to us through the
senses, and cannot, therefore, be already contained in the pure
form of sensible intuition. For it is an act of spontaneity of the
faculty of representation; and since this faculty, to distinguish
it from sensibility, must be entitled understanding, all com-
bination -- be we conscious of it or not, be it a combination of
the manifold of intuition, empirical or non-empirical, or of
various concepts -- is an act of the understanding. To this act
the general title 'synthesis' may be assigned, as indicating
that we cannot represent to ourselves anything as combined in
the object which we have not ourselves previously combined,
and that of all representations combination is the only one which
P 152
cannot be given through objects. Being an act of the self-
activity of the subject, it cannot be executed save by the sub-
ject itself. It will easily be observed that this action is originally
one and is equipollent for all combination, and that is dis-
solution, namely, analysis, which appears to be its opposite,
yet always presupposes it. For where the understanding has
not previously combined, it cannot dissolve, since only as
having been combined by the understanding can anything that
allows of analysis be given to the faculty of representation. 
 But the concept of combination includes, besides the con-
cept of the manifold and of its synthesis, also the concept of
the unity of the manifold. Combination is representation of the
synthetic unity of the manifold. The representation of this
unity cannot, therefore, arise out of the combination. On the
contrary, it is what, by adding itself to the representation of
the manifold, first makes possible the concept of the combina-
tion. This unity, which precedes a priori all concepts of com-
bination, is not the category of unity ($10); for all categories
are grounded in logical functions of judgment, and in these
functions combination, and therefore unity of given concepts,
is already thought. Thus the category already presupposes
combination. We must therefore look yet higher for this unity
(as qualitative, $12), namely in that which itself contains the
ground of the unity of diverse concepts in judgment, and there-
fore of the possibility of the understanding, even as regards
its logical employment. 
The Original Synthetic Unity of Apperception 
 It must be possible for the 'I think' to accompany all my
representations; for otherwise something would be represented
P 153
in me which could not be thought at all, and that is equivalent
to saying that the representation would be impossible, or at
least would be nothing to me. 
P 152
 Whether the representations are in themselves identical, and
whether, therefore, one can be analytically thought through the
other, is not a question that here arises. The consciousness of the one,
when the manifold is under consideration, has always to be dis-
tinguished from the consciousness of the other; and it is with the
synthesis of this (possible) consciousness that we are here alone
P 153
That representation which can
be given prior to all thought is entitled intuition. All the
manifold of intuition has, therefore, a necessary relation to the
'I think' in the same subject in which this manifold is found. 
But this representation is an act of spontaneity, that is, it
cannot be regarded as belonging to sensibility. I call it pure
apperception, to distinguish it from empirical apperception, or,
again, origninal apperception, because it is that self-consious-
ness which, while generating the representation 'I think' (a
representation which must be capable of accompanying all
other representations, and which in all consciousness is one and
the same), cannot itself be accompanied by any further repre-
sentation. The unity of this apperception I likewise entitle the
transcendental unity of self-consciousness, in order to indicate
the possibility of a priori knowledge arising from it. For the
manifold representations, which are given in an intuition,
would not be one and all my representations, if they did
not all belong to one self-consciousness. As my representa-
tions (even if I am not conscious of them as such) they
must conform to the condition under which alone they can
stand together in one universal self-consciousness, because
otherwise they would not all without exception belong to
me. From this original combination many consequences
 This thoroughgoing identity of the apperception of a
manifold which is given in intuition contains a synthesis of
representations, and is possible only through the conscious-
ness of this synthesis. For the empirical consciousness, which
accompanies different representations, is in itself diverse and
without relation to the identity of the subject. That relation
comes about, not simply through my accompanying each re-
presentation with consciousness, but only in so far as I conjoin
one representation with another, and am conscious of the syn-
thesis of them. Only in so far, therefore, as I can unite a
manifold of given representations in one consciousness, is it
possible for me to represent to myself the identity of the con-
sciousness in [i.e. throughout] these representations. In other
P 154
words, the analytic unity of apperception is possible only under
the presupposition of a certain synthetic unity. 
 The thought that the representations given in intuition one
and all belong to me, is therefore equivalent to the thought
that I unite them in one self-consciousness, or can at least
so unite them; and although this thought is not itself the
consciousness of the synthesis of the representations, it pre-
supposes the possibility of that synthesis. In other words, only
in so far as I can grasp the manifold of the representations in
one consciousness, do I call them one and all mine. For other-
wise I should have as many-coloured and diverse a self as I
have representations of which I am conscious to myself. Syn-
thetic unity of the manifold of intuitions, as generated a -
priori, is thus the ground of the identity of apperception itself,
which precedes a priori all my determinate thought. Com-
bination does not, however, lie in the objects, and cannot be
borrowed from them, and so, through perception, first taken up
into the understanding. On the contrary, it is an affair of the
understanding alone, which itself is nothing but the faculty
of combining a priori, and of bringing the manifold of given
representations under the unity of apperception. The principle
of apperception is the highest principle in the whole sphere of
human knowledge. 
This principle of the necessary unity of apperception is
++ The analytic unity of consciousness belongs to all general con-
cepts, as such. If, for instance, I think red in general, I thereby repre-
sent to myself a property which (as a characteristic) can be found in
something, or can he combined with other representations; that is,
only by means of a presupposed possible synthetic unity can I repre-
sent to myself the analytic unity. A representation which is to be
thought as common to different representations is regarded as be-
longing to such as have, in addition to it, also something different. 
Consequently it must previously be thought in synthetic unity with
other (though, it may be, only possible) representations, before I can
think in it the analytic unity of consciousness, which makes it a con-
ceptus communis. The synthetic unity of apperception is therefore
that highest point, to which we must ascribe all employment of the
understanding, even the whole of logic, and conformably therewith,
transcendental philosophy. Indeed this faculty of apperception is the
understanding itself. 
P 155
itself, indeed, an identical, and therefore analytic, proposi-
tion; nevertheless it reveals the necessity of a synthesis of the
manifold given in intuition, without which the thoroughgoing
identity of self-consciousness cannot be thought. For through
the 'I', as simple representation, nothing manifold is given;
only in intuition, which is distinct from the 'I', can a manifold
be given; and only through combination in one conscious-
ness can it be thought. An understanding in which through
self-consciousness all the manifold would eo ipso be given,
would be intuitive; our understanding can only think, and
for intuition must look to the senses. I am conscious of the
self as identical in respect of the manifold of representations
that are given to me in an intuition, because I call them one
and all my representations, and so apprehend them as con-
stituting one intuition. This amounts to saying, that I am
conscious to myself a priori of a necessary synthesis of re-
presentations -- to be entitled the original synthetic unity of
apperception -- under which all representations that are given
to me must stand, but under which they have also first to
be brought by means of a synthesis. 
The Principle of the Synthetic Unity is the Supreme
Principle of all Employment of the Understanding 
The supreme principle of the possibility of all intuition in
its relation to sensibility is, according to the Transcendental
Aesthetic, that all the manifold of intuition should be subject
to the formal conditions of space and time. The supreme prin-
ciple of the same possibility, in its relation to understanding,
is that all the manifold of intuition should be subject to con-
ditions of the original synthetic unity of apperception. 
 Space and time, and all their parts, are intuitions, and are,
therefore, with the manifold which they contain, singular representa-
tions (vide the Transcendental Aesthetic). Consequently they are not
mere concepts through which one and the same consciousness is
found to be contained in a number of representations. On the con-
trary, through them many representations are found to be contained
in one representation, and in the consciousness of that representa-
tion ; and they are thus composite. The unity of that consciousness
P 156n
is therefore synthetic and yet is also original. The singularity of such
intuitions is found to have important consequences (vide $25). 
P 155
In so
P 156
far as the manifold representations of intuition are given to us,
they are subject to the former of these two principles; in so far
as they must allow of being combined in one consciousness,
they are subject to the latter. For without such combination
nothing can be thought or known, since the given repre-
sentations would not have in common the act of the apper-
ception 'I think', and so could not be apprehended together in
knowledge. This knowledge consists in the determinate re-
lation of given representations to an object; and an object is
that in the concept of which the manifold of a given intuition
is united. Now all unification of representations demands
unity of consciousness in the synthesis of them. Consequently
it is the unity of consciousness that alone constitutes the
relation of representations to an object, and therefore their
objective validity and the fact that they are modes of know-
ledge; and upon it therefore rests the very possibility of the
The first pure knowledge of understanding, then, upon
which all the rest of its employment is based, and which also
at the same time is completely independent of all conditions
of sensible intuition, is the principle of the original synthetic
unity of apperception. Thus the mere form of outer sensible
intuition, space, is not yet [by itself] knowledge; it supplies
only the manifold of a priori intuition for a possible know-
ledge. To know anything in space (for instance, a line), I
must draw it, and thus synthetically bring into being a de-
terminate combination of the given manifold, so that the unity
of this act is at the same time the unity of consciousness (as
in the concept of a line); and it is through this unity of con-
sciousness that an object (a determinate space) is first known. 
The synthetic unity of consciousness is, therefore, an objective
condition of all knowledge. It is not merely a condition that
I myself require in knowing an object, but is a condition
under which every intuition must stand in order to become
an object for me. For otherwise, in the absence of this
P 157
synthesis, the manifold would not be united in one con-
Although this proposition makes synthetic unity a con-
dition of all thought, it is, as already stated, itself analytic. 
For it says no more than that all my representations in any
given intuition must be subject to that condition under which
alone I can ascribe them to the identical self as my representa-
tions, and so can comprehend them as synthetically com-
bined in one apperception through the general expression,
'I think'. 
This principle is not, however, to be taken as applying
to every possible understanding, but only to that understand-
ing through whose pure apperception, in the representation
'I am', nothing manifold is given. An understanding which
through its self-consciousness could supply to itself the mani-
fold of intuition -- an understanding, that is to say, through
whose representation the objects of the representation should
at the same time exist -- would not require, for the unity of
consciousness, a special act of synthesis of the manifold. For
the human understanding, however, which thinks only, and
does not intuit, that act is necessary. It is indeed the first
principle of the human understanding, and is so indispensable
to it that we cannot form the least conception of any other
possible understanding, either of such as is itself intuitive or
of any that may possess an underlying mode of sensible in-
tuition which is different in kind from that in space and time. 
The Objective Unity of Self-Consciousness 
The transcendental unity of apperception is that unity
through which all the manifold given in an intuition is united
in a concept of the object. It is therefore entitled objective,
and must be distinguished from the subjective unity of con-
sciousness, which is a determination of inner sense -- through
which the manifold of intuition for such [objective] combina-
tion is empirically given. Whether I can become empirically
conscious of the manifold as simultaneous or as successive
depends on circumstances or empirical conditions. Therefore
P 158
the empirical unity of consciousness, through association of
representations, itself concerns an appearance, and is wholly
contingent. But the pure form of intuition in time, merely
as intuition in general, which contains a given manifold, is
subject to the original unity of consciousness, simply through
the necessary relation of the manifold of the intuition to
the one 'I think', and so through the pure synthesis of
understanding which is the a priori underlying ground of
the empirical synthesis. Only the original unity is objectively
valid; the empirical unity of apperception, upon which we
are not here dwelling, and which besides is merely derived
from the former under given conditions in concreto, has only
subjective validity. To one man, for instance, a certain word
suggests one thing, to another some other thing; the unity
of consciousness in that which is empirical is not, as regards
what is given, necessarily and universally valid. 
The Logical Form of all Judgments consists in the Objective
Unity of the Apperception of the Concepts which they
I have never been able to accept the interpretation which
logicians give of judgment in general. It is, they declare,
the representation of a relation between two concepts. I do
not here dispute with them as to what is defective in this
interpretation -- that in any case it applies only to categorical,
not to hypothetical and disjunctive judgments (the two latter
containing a relation not of concepts but of judgments), an
oversight from which many troublesome consequences have
followed. I need only point out that the definition does not
determine in what the asserted relation consists. 
 The lengthy doctrine of the four syllogistic figures concerns
categorical syllogisms only; and although it is indeed nothing more
than an artificial method of securing, through the surreptitious
introduction of immediate inferences (consequentiae immediatae)
among the premisses of a pure syllogism, the appearance that there
are more kinds of inference than that of the first figure, this would
hardly have met with such remarkable acceptance, had not its
authors succeeded in bringing categorical judgments into such
P 159n
exclusive respect, as being those to which all others must allow of
being reduced -- teaching which, as indicated in $9, is none the less
P 159
But if I investigate more precisely the relation of the given
modes of knowledge in any judgment, and distinguish it,
as belonging to the understanding, from the relation accord-
ing to laws of the reproductive imagination, which has
only subjective validity, I find that a judgment is nothing
but the manner in which given modes of knowledge are
brought to the objective unity of apperception. This is what
is intended by the copula 'is'. It is employed to distinguish
the objective unity of given representations from the sub-
jective. It indicates their relation to original apperception,
and its necessary unity. It holds good even if the judgment
is itself empirical, and therefore contingent, as, for example,
in the judgment, 'Bodies are heavy'. I do not here assert that
these representations necessarily belong to one another in the
empirical intuition, but that they belong to one another in
virtue of the necessary unity of apperception in the synthesis
of intuitions, that is, according to principles of the object-
ive determination of all representations, in so far as know-
ledge can be acquired by means of these representations --
principles which are all derived from the fundamental prin-
ciple of the transcendental unity of apperception. Only in this
way does there arise from this relation a judgment, that is, a
relation which is objectively valid, and so can be adequately
distinguished from a relation of the same representations
that would have only subjective validity -- as when they are
connected according to laws of association. In the latter case,
all that I could say would be, 'If I support a body, I feel an
impression of weight'; I could not say, 'It, the body, is heavy'. 
Thus to say 'The body is heavy' is not merely to state that
the two representations have always been conjoined in my
perception, however often that perception be repeated; what
we are asserting is that they are combined in the object, no
matter what the state of the subject may be. 
P 160
All Sensible Intuitions are subject to the Categories, as Con-
ditions under which alone their Manifold can come to-
gether in one Consciousness 
The manifold given in a sensible intuition is necessarily
subject to the original synthetic unity of apperception, be-
cause in no other way is the unity of intuition possible ($17). 
But that act of understanding by which the manifold of given
representations (be they intuitions or concepts) is brought
under one apperception, is the logical function of judgment
(cf. $19). All the manifold, therefore, so far as it is given in a
single empirical intuition, is determined in respect of one of
the logical functions of judgment, and is thereby brought into
one consciousness. Now the categories are just these functions
of judgment, in so far as they are employed in determination
of the manifold of a given intuition (cf. $13). Consequently,
the manifold in a given intuition is necessarily subject to the
A manifold, contained in an intuition which I call mine, is
represented, by means of the synthesis of the understanding, as
belonging to the necessary unity of self-consciousness; and this
is effected by means of the category. This [requirement of a]
category therefore shows that the empirical consciousness of a
given manifold in a single intuition is subject to a pure self-
consciousness a priori, just as is empirical intuition to a pure
sensible intuition, which likewise takes place a priori. Thus in
the above proposition a beginning is made of a deduction of
the pure concepts of understanding; 
 The proof of this rests on the represented unity of intuition, by
which an object is given. This unity of intuition always includes in
itself a synthesis of the manifold given for an intuition, and so
already contains the relation of this manifold to the unity of apper-
P 160
and in this deduction,
since the categories have their source in the understanding
alone, independently of sensibility, I must abstract from the
P 161
mode in which the manifold for an empirical intuition is given,
and must direct attention solely to the unity which, in terms of
the category, and by means of the understanding, enters into
the intuition. In what follows (cf. $26) it will be shown, from
the mode in which the empirical intuition is given in sensibil-
ity, that its unity is no other than that which the category
(according to $20) prescribes to the manifold of a given in-
tuition in general. Only thus, by demonstration of the a priori
validity of the categories in respect of all objects of our senses,
will the purpose of the deduction be fully attained. 
But in the above proof there is one feature from which I
could not abstract, the feature, namely, that the manifold to be
intuited must be given prior to the synthesis of understanding,
and independently of it. How this takes place, remains here
undetermined. For were I to think an understanding which is
itself intuitive (as, for example, a divine understanding which
should not represent to itself given objects, but through whose
representation the objects should themselves be given or pro-
duced), the categories would have no meaning whatsoever in
respect of such a mode of knowledge. They are merely rules for
an understanding whose whole power consists in thought, con-
sists, that is, in the act whereby it brings the synthesis of a mani-
fold, given to it from elsewhere in intuition, to the unity of ap-
perception -- a faculty, therefore, which by itself knows nothing
whatsoever, but merely combines and arranges the material of
knowledge, that is, the intuition, which must be given to it by
the object. This peculiarity of our understanding, that it can
produce a priori unity of apperception solely by means of the
categories, and only by such and so many, is as little capable
of further explanation as why we have just these and no other
functions of judgment, or why space and time are the only
forms of our possible intuition. 
The Category has no other Application in Knowledge
than to Objects of Experience 
To think an object and to know an object are thus by no
means the same thing. Knowledge involves two factors: first,
P 162
the concept, through which an object in general is thought (the
category); and secondly, the intuition, through which it is
given. For if no intuition could be given corresponding to the
concept, the concept would still indeed be a thought, so far as
its form is concerned, but would be without any object, and no
knowledge of anything would be possible by means of it. So
far as I could know, there would be nothing, and could be
nothing, to which my thought could be applied. Now, as the
Aesthetic has shown, the only intuition possible to us is sens-
ible; consequently, the thought of an object in general, by
means of a pure concept of understanding, can become know-
ledge for us only in so far as the concept is related to objects
of the senses. Sensible intuition is either pure intuition (space
and time) or empirical intuition of that which is immediately
represented, through sensation, as actual in space and time. 
Through the determination of pure intuition we can acquire
a priori knowledge of objects, as in mathematics, but only
in regard to their form, as appearances; whether there can be
things which must be intuited in this form, is still left unde-
cided. Mathematical concepts are not, therefore, by themselves
knowledge, except on the supposition that there are things
which allow of being presented to us only in accordance with
the form of that pure sensible intuition. Now things in space
and time are given only in so far as they are perceptions
(that is, representations accompanied by sensation) -- therefore
only through empirical representation. Consequently, the pure
concepts of understanding, even when they are applied to a -
priori intuitions, as in mathematics, yield knowledge only in
so far as these intuitions -- and therefore indirectly by their
means the pure concepts also -- can be applied to empirical in-
tuitions. Even, therefore, with the aid of [pure] intuition, the
categories do not afford us any knowledge of things; they do
so only through their possible application to empirical intui-
tion. In other words, they serve only for the possibility of em-
pirical knowledge; and such knowledge is what we entitle
experience. Our conclusion is therefore this: the categories,
as yielding knowledge of things, have no kind of application,
save only in regard to things which may be objects of possible
P 163
The above proposition is of the greatest importance; for it
determines the limits of the employment of the pure concepts
of understanding in regard to objects, just as the Transcen-
dental Aesthetic determined the limits of the employment of
the pure form of our sensible intuition. Space and time, as con-
ditions under which alone objects can possibly be given to us,
are valid no further than for objects of the senses, and there-
fore only for experience. Beyond these limits they represent
nothing; for they are only in the senses, and beyond them have
no reality. The pure concepts of understanding are free from
this limitation, and extend to objects of intuition in general,
be the intuition like or unlike ours, if only it be sensible and
not intellectual. But this extension of concepts beyond our
sensible intuition is of no advantage to us. For as concepts of
objects they are then empty, and do not even enable us to
judge of their objects whether or not they are possible. They
are mere forms of thought, without objective reality, since
we have no intuition at hand to which the synthetic unity
of apperception, which constitutes the whole content of these
forms, could be applied, and in being so applied determine
an object. Only our sensible and empirical intuition can give
to them body and meaning. 
If we suppose an object of a non-sensible intuition to be
given, we can indeed represent it through all the predicates
which are implied in the presupposition that it has none of the
characteristics proper to sensible intuition; that it is not ex-
tended or in space, that its duration is not a time, that no
change (succession of determinations in time) is to be met with
in it, etc. But there is no proper knowledge if I thus merely in-
dicate what the intuition of an object is not, without being able
to say what it is that is contained in the intuition. For I have
not then shown that the object which I am thinking through
my pure concept is even so much as possible, not being in a
position to give any intuition corresponding to the concept,
and being able only to say that our intuition is not applicable to
it. But what has chiefly to be noted is this, that to such a some-
thing [in general] not a single one of all the categories could
P 164
be applied. We could not, for instance, apply to it the concept
of substance, meaning something which can exist as subject
and never as mere predicate. For save in so far as empirical
intuition provides the instance to which to apply it, I do not
know whether there can be anything that corresponds to such
a form of thought. But of this more hereafter. 
The Application of the Categories to Objects of the Senses
in General 
The pure concepts of understanding relate, through the
mere understanding, to objects of intuition in general, whether
that intuition be our own or any other, provided only it be
sensible. The concepts are, however, for this very reason, mere
forms of thought, through which alone no determinate object is
known. The synthesis or combination of the manifold in them
relates only to the unity of apperception, and is thereby the
ground of the possibility of a priori knowledge, so far as such
knowledge rests on the understanding. This synthesis, there-
fore, is at once transcendental and also purely intellectual. But
since there lies in us a certain form of a priori sensible intui-
tion, which depends on the receptivity of the faculty of repre-
sentation (sensibility), the understanding, as spontaneity, is able
to determine inner sense through the manifold of given repre-
sentations, in accordance with the synthetic unity of apper-
ception, and so to think synthetic unity of the apperception
of the manifold of a priori sensible intuition -- that being the
condition under which all objects of our human intuition must
necessarily stand. In this way the categories, in themselves
mere forms of thought, obtain objective reality, that is, ap-
plication to objects which can be given us in intuition. These
objects, however, are only appearances, for it is solely of
appearances that we can have a priori intuition. 
This synthesis of the manifold of sensible intuition, which
is possible and necessary a priori, may be entitled figurative
synthesis (synthesis speciosa), to distinguish it from the syn-
thesis which is thought in the mere category in respect of the
manifold of an intuition in general, and which is entitled
combination through the understanding (synthesis intellectua-
P 165
lis). Both are transcendental, not merely as taking place
a priori, but also as conditioning the possibility of other
a priori knowledge. 
But the figurative synthesis, if it be directed merely
to the original synthetic unity of apperception, that is, to
the transcendental unity which is thought in the categories,
must, in order to be distinguished from the merely intellec-
tual combination, be called the transcendental synthesis of
imagination. Imagination is the faculty of representing in
intuition an object that is not itself present. Now since all our
intuition is sensible, the imagination, owing to the subjective
condition under which alone it can give to the concepts of
understanding a corresponding intuition, belongs to sen-
sibility. But inasmuch as its synthesis is an expression of
spontaneity, which is determinative and not, like sense, deter-
minable merely, and which is therefore able to determine
sense a priori in respect of its form in accordance with the
unity of apperception, imagination is to that extent a faculty
which determines the sensibility a priori; and its synthesis of
intuitions, conforming as it does to the categories, must be
the transcendental synthesis of imagination. This synthesis is
an action of the understanding on the sensibility; and is
its first application -- and thereby the ground of all its other
applications -- to the objects of our possible intuition. As
figurative, it is distinguished from the intellectual synthesis,
which is carried out by the understanding alone, without the
aid of the imagination. In so far as imagination is spontaneity,
I sometimes also entitle it the productive imagination, to dis-
tinguish it from the reproductive imagination, whose synthesis
is entirely subject to empirical laws, the laws, namely, of
association, and which therefore contributes nothing to the
explanation of the possibility of a priori knowledge. The repro-
ductive synthesis falls within the domain, not of transcendental
philosophy, but of psychology. 
* * *
This is a suitable place for explaining the paradox which
must have been obvious to everyone in our exposition of the
P 166
form of inner sense ($6): namely, that this sense represents
to consciousness even our own selves only as we appear to
ourselves, not as we are in ourselves. For we intuit ourselves
only as we are inwardly affected, and this would seem to be
contradictory, since we should then have to be in a passive
relation [of active affection] to ourselves. It is to avoid this
contradiction that in systems of psychology inner sense,
which we have carefully distinguished from the faculty
of apperception, is commonly regarded as being identical
with it. 
What determines inner sense is the understanding and its
original power of combining the manifold of intuition, that is,
of bringing it under an apperception, upon which the possi-
bility of understanding itself rest. Now the understanding
in us men is not a faculty of intuitions, and cannot,
even if intuitions be given in sensibility, take them up into
itself in such manner as to combine them as the manifold of
its own intuition. Its synthesis, therefore, if the synthesis be
viewed by itself alone, is nothing but the unity of the act,
of which, as an act, it is conscious to itself, even without
[the aid of] sensibility, but through which it is yet able to
determine the sensibility. The understanding, that is to say,
in respect of the manifold which may be given to it in accord-
ance with the form of sensible intuition, is able to deter-
mine sensibility inwardly. Thus the understanding, under
the title of a transcendental synthesis of imagination, performs
this act upon the passive subject, whose faculty it is, and we
are therefore justified in saying that inner sense is affected
thereby. Apperception and its synthetic unity is, indeed, very
far from being identical with inner sense. The former, as the
source of all combination, applies to the manifold of intui-
tions in general, and in the guise of the categories, prior
to all sensible intuition, to objects in general. Inner sense,
on the other hand, contains the mere form of intuition, but
without combination of the manifold in it, and therefore so
far contains no determinate intuition, which is possible only
through the consciousness of the determination of the manifold
by the transcendental act of imagination (synthetic influence
P 167
of the understanding upon inner sense), which I have entitled
figurative synthesis. 
This we can always perceive in ourselves. We cannot think
a line without drawing it in thought, or a circle without
describing it. We cannot represent the three dimensions of
space save by setting three lines at right angles to one another
from the same point. Even time itself we cannot represent,
save in so far as we attend, in the drawing of a straight line
(which has to serve as the outer figurative representation of
time), merely to the act of the synthesis of the manifold where-
by we successively determine inner sense, and in so doing
attend to the succession of this determination in inner sense. 
Motion, as an act of the subject (not as a determination of
an object), and therefore the synthesis of the manifold in
space, first produces the concept of succession -- if we abstract
from this manifold and attend solely to the act through which
we determine the inner sense according to its form. The
understanding does not, therefore, find in inner sense such
a combination of the manifold, but produces it, in that it
affects that sense.
How the 'I' that thinks can be distinct from the 'I' that
intuits itself (for I can represent still other modes of intuition
as at least possible), and yet, as being the same subject, can be
identical with the latter; and how, therefore, I can say: "I, as
intelligence and thinking subject, know myself as an object
that is thought, in so far as I am given to myself [as some-
thing other or] beyond that [I] which is [given to myself] in
intuition, and yet know myself, like other phenomena, only
as I appear to myself, not as I am to the understanding" --
these are questions that raise no greater nor less difficulty
than how I can be an object to myself at all, and, more
particularly, an object of intuition and of inner perceptions. 
 Motion of an object in space does not belong to a pure science,
and consequently not to geometry. For the fact that something is
movable cannot be known a priori, but only through experience. 
Motion, however, considered as the describing of a space, is a pure
act of the successive synthesis of the manifold in outer intuition in
general by means of the productive imagination, and belongs not
only to geometry, but even to transcendental philosophy. 
P 168
Indeed, that this is how it must be, is easily shown -- if we
admit that space is merely a pure form of the appearances of
outer sense -- by the fact that we cannot obtain for ourselves
a representation of time, which is not an object of outer in-
tuition, except under the image of a line, which we draw, and
that by this mode of depicting it alone could we know the
singleness of its dimension; and similarly by the fact that
for all inner perceptions we must derive the determination of
lengths of time or of points of time from the changes which
are exhibited to us in outer things, and that the determina-
tions of inner sense have therefore to be arranged as appear-
ances in time in precisely the same manner in which we
arrange those of outer sense in space. If, then, as regards the
latter, we admit that we know objects only in so far as we
are externally affected, we must also recognise, as regards
inner sense, that by means of it we intuit ourselves only as
we are inwardly affected by ourselves; in other words, that,
so far as inner intuition is concerned, we know our own
subject only as appearance, not as it is in itself. 
On the other hand, in the transcendental synthesis of the
manifold of representations in general, and therefore in the
synthetic original unity of apperception, I am conscious of
myself, not as I appear to myself, nor as I am in myself, but
only that I am. This representation is a thought, not an intui-
tion. Now in order to know ourselves, there is required in
addition to the act of thought, which brings the manifold
of every possible intuition to the unity of apperception, a de-
terminate mode of intuition, whereby this manifold is given; 
++ I do not see why so much difficulty should be found in admit-
ting that our inner sense is affected by ourselves. Such affection finds
exemplification in each and every act of attention. In every act of
attention the understanding determines inner sense, in accordance
with the combination which it thinks, to that inner intuition which
corresponds to the manifold in the synthesis of the understanding. 
How much the mind is usually thereby affected, everyone will be
able to perceive in himself. 
P 168
it therefore follows that although my existence is not indeed
P 169
appearance (still less mere illusion), the determination of my
existence can take place only in conformity with the form of
inner sense, according to the special mode in which the mani-
fold, which I combine, is given in inner intuition. Accordingly
I have no knowledge of myself as I am but merely as I appear
to myself. The consciousness of self is thus very far from being
a knowledge of the self, notwithstanding all the categories
which [are being employed to] constitute the thought of an
object in general, through combination of the manifold in one
apperception. Just as for knowledge of an object distinct from
me I require, besides the thought of an object in general
(in the category), an intuition by which I determine that
general concept, so for knowledge of myself I require, besides
the consciousness, that is, besides the thought of myself, an
intuition of the manifold in me, by which I determine this
thought. I exist as an intelligence which is conscious solely
of its power of combination; but in respect of the manifold
which it has to combine I am subjected to a limiting condition
(entitled inner sense), namely, that this combination can be
made intuitable only according to relations of time, which
lie entirely outside the concepts of understanding, strictly re-
garded. Such an intelligence, therefore, can know itself only
as it appears to itself in respect of an intuition which is not
intellectual and cannot be given by the understanding itself,
not as it would know itself if its intuition were intellectual. 
++ The 'I think' expresses the act of determining my existence. 
Existence is already given thereby, but the mode in which I am to
determine this existence, that is, the manifold belonging to it, is not
thereby given. In order that it be given, self-intuition is required;
and such intuition is conditioned by a given a priori form, namely,
time, which is sensible and belongs to the receptivity of the deter-
minable [in me]. Now since I do not have another self-intuition
which gives the determining in me (I am conscious only of the
spontaneity of it) prior to the act of determination, as time does
in the case of the determinable, I cannot determine my existence
as that of a self-active being; all that I can do is to represent to
myself the spontaneity of my thought, that is, of the determination;
and my existence is still only determinable sensibly, that is, as the
existence of an appearance. But it is owing to this spontaneity that
I entitle myself an intelligence. 
P 170
Transcendental Deduction of the Universally Possible Em-
ployment in experience of the Pure Concepts of the
In the metaphysical deduction the a priori origin of the
categories has been proved through their complete agreement
with the general logical functions of thought; in the transcen-
dental deduction we have shown their possibility as a priori
modes of knowledge of objects of an intuition in general
(cf. $$20, 21). We have now to explain the possibility of
knowing a priori, by means of categories, whatever objects
may present themselves to our senses, not indeed in respect
of the form of their intuition, but in respect of the laws of
their combination, and so, as it were, of prescribing laws to
nature, and even of making nature possible. For unless the cate-
gories discharged this function, there could be no explaining
why everything that can be presented to our senses must be
subject to laws which have their origin a priori in the under-
standing alone. 
First of all, I may draw attention to the fact that by syn-
thesis of apprehension I understand that combination of the
manifold in an empirical intuition, whereby perception, that
is, empirical consciousness of the intuition (as appearance),
is possible. 
In the representations of space and time we have a priori
forms of outer and inner sensible intuition; and to these the
synthesis of apprehension of the manifold of appearance must
always conform, because in no other way can the synthesis
take place at all. But space and time are represented a priori
not merely as forms of sensible intuition, but as themselves
intuitions which contain a manifold [of their own], and there-
fore are represented with the determination of the unity
of this manifold (vide the Transcendental Aesthetic). Thus
P 171
unity of the synthesis of the manifold, without or within us,
and consequently also a combination to which everything that
is to be represented as determined in space or in time must
conform, is given a priori as the condition of the synthesis
of all apprehension -- not indeed in, but with these intuitions. 
This synthetic unity can be no other than the unity of the
combination of the manifold of a given intuition in general
in an original consciousness, in accordance with the cate-
gories, in so far as the combination is applied to our sensible
intuition. All synthesis, therefore, even that which renders
perception possible, is subject to the categories; and since
experience is knowledge by means of connected perceptions,
the categories are conditions of the possibility of experience,
and are therefore valid a priori for all objects of experience. 
* * *
When, for instance, by apprehension of the manifold of a
house I make the empirical intuition of it into a perception,
the necessary unity of space and of outer sensible intuition in
general lies at the basis of my apprehension, and I draw as it
were the outline of the house in conformity with this synthetic
unity of the manifold in space. But if I abstract from the form
of space, this same synthetic unity has its seat in the under-
standing, and is the category of the synthesis of the homogene-
ous in an intuition in general, that is, the category of quantity. 
To this category, therefore, the synthesis of apprehension, that
is to say, the perception, must completely conform. 
P 170n
++ Space, represented as object (as we are required to do in geo-
metry), contains more than mere form of intuition; it also contains
combination of the manifold, given according to the form of sensi-
bility, in an intuitive representation, so that the form of intuition
gives only a manifold, the formal intuition gives unity of representa-
tion. In the Aesthetic I have treated this unity as belonging merely
P 171n
to sensibility, simply in order to emphasise that it precedes any con-
cept, although, as a matter of fact, it presupposes a synthesis which
does not belong to the senses but through which all concepts of
space and time first become possible. For since by its means (in that
the understanding determines the sensibility) space and time are
first given as intuitions, the unity of this a priori intuition belongs to
space and time, and not to the concept of the understanding (cf.
++ In this manner it is proved that the synthesis of apprehension,
which is empirical, must necessarily be in conformity with the syn-
thesis of apperception, which is intellectual and is contained in the
category completely a priori. It is one and the same spontaneity,
P 172n
which in the one case, under the title of imagination, and in the other
case, under the title of understanding, brings combination into the
manifold of intuition. 
P 172
When, to take another example, I perceive the freezing of
water, I apprehend two states, fluidity and solidity, and these
as standing to one another in a relation of time. But in time,
which I place at the basis of the appearance [in so far] as
[it is] inner intuition, I necessarily represent to myself synthetic
unity of the manifold, without which that relation of time could
not be given in an intuition as being determined in respect of
time-sequence. Now this synthetic unity, as a condition
a priori under which I combine the manifold of an intui-
tion in general, is -- if I abstract from the constant form of
my inner intuition, namely, time -- the category of cause, by
means of which, when I apply it to my sensibility, I deter-
mine everything that happens in accordance with the relation
which it prescribes, and I do so in time in general. Thus my
apprehension of such an event, and therefore the event itself,
considered as a possible perception, is subject to the con-
cept of the relation of effects and causes, and so in all other
Categories are concepts which prescribe laws a priori to
appearances, and therefore to nature, the sum of all appear-
ances (natura materialiter spectata). The question therefore
arises, how it can be conceivable that nature should have to
proceed in accordance with categories which yet are not de-
rived from it, and do not model themselves upon its pattern;
that is, how they can determine a priori the combination of
the manifold of nature, while yet they are not derived from it. 
The solution of this seeming enigma is as follows. 
 That the laws of appearances in nature must agree with the
understanding and its a priori form, that is, with its faculty
of combining the manifold in general, is no more surprising
than that the appearances themselves must agree with the form
of a priori sensible intuition. For just as appearances do not
exist in themselves but only relatively to the subject in which,
so far as it has senses, they inhere, so the laws do not exist in
the appearances but only relatively to this same being, so far as
it has understanding. Things in themselves would necessarily,
P 173
apart from any understanding that knows them, conform to
laws of their own. But appearances are only representations of
things which are unknown as regards what they may be in
themselves. As mere representations, they are subject to no
law of connection save that which the connecting faculty pre-
scribes. Now it is imagination that connects the manifold of
sensible intuition; and imagination is dependent for the unity
of its intellectual synthesis upon the understanding, and for
the manifoldness of its apprehension upon sensibility. All
possible perception is thus dependent upon synthesis of appre-
hension, and this empirical synthesis in turn upon transcen-
dental synthesis, and therefore upon the categories. Conse-
quently, all possible perceptions, and therefore everything that
can come to empirical consciousness, that is, all appearances
of nature, must, so far as their connection is concerned, be sub-
ject to the categories. Nature, considered merely as nature in
general, is dependent upon these categories as the original
ground of its necessary conformity to law (natura formaliter
spectata). Pure understanding is not, however, in a position,
through mere categories, to prescribe to appearances any
a priori laws other than those which are involved in a nature
in general, that is, in the conformity to law of all appearances
in space and time. Special laws, as concerning those appear-
ances which are empirically determined, cannot in their specific
character be derived from the categories, although they are
one and all subject to them. To obtain any knowledge what-
soever of these special laws, we must resort to experience; but
it is the a priori laws that alone can instruct us in regard to
experience in general, and as to what it is that can be known
as an object of experience. 
Outcome of this Deduction of the Concepts of
We cannot think an object save through categories; we
cannot know an object so thought save through intuitions
corresponding to these concepts. Now all our intuitions are
sensible; and this knowledge, in so far as its object is given, is
empirical. But empirical knowledge is experience. Conse-
P 174
quently, there can be no a priori knowledge, except of objects
of possible experience. 
But although this knowledge is limited to objects of ex-
perience, it is not therefore all derived from experience. The
pure intuitions [of receptivity] and the pure concepts of under-
standing are elements in knowledge, and both are found in us
a priori. There are only two ways in which we can account for
a necessary agreement of experience with the concepts of its
objects: either experience makes these concepts possible or these
concepts make experience possible. The former supposition
does not hold in respect of the categories (nor of pure sensible
intuition); for since they are a priori concepts, and there-
fore independent of experience, the ascription to them of an
empirical origin would be a sort of generatio aequivoca. There
remains, therefore, only the second supposition -- a system, as
it were, of the epigenesis of pure reason -- namely, that the cate-
gories contain, on the side of the understanding, the grounds
of the possibility of all experience in general. How they make
experience possible, and what are the principles of the possi-
bility of experience that they supply in their application to
appearances, will be shown more fully in the following chapter
on the transcendental employment of the faculty of judgment. 
A middle course may be proposed between the two above
mentioned, namely, that the categories are neither self-thought
first principles a priori of our knowledge nor derived from ex-
perience, but subjective dispositions of thought, implanted in
us from the first moment of our existence, and so ordered by
our Creator that their employment is in complete harmony
with the laws of nature in accordance with which experience
P 175
proceeds -- a kind of preformation-system of pure reason. 
P 174n
++ Lest my readers should stumble at the alarming evil con-
sequences which may over-hastily be inferred from this statement, I
may remind them that for thought the categories are not limited by
the conditions of our sensible intuition, but have an unlimited field. 
It is only the knowledge of that which we think, the determining of
the object, that requires intuition. In the absence of intuition, the
thought of the object may still have its true and useful consequences,
as regards the subject's employment of reason. The use of reason is
not always directed to the determination of an object, that is, to know-
ledge, but also to the determination of the subject and of its volition
-- a use which cannot be here dealt with. 
P 175
Apart, however, from the objection that on such an hypo-
thesis we can set no limit to the assumption of predetermined
dispositions to future judgments, there is this decisive objec-
tion against the suggested middle course, that the necessity
of the categories, which belongs to their very conception,
would then have to be sacrificed. The concept of cause, for
instance, which expresses the necessity of an event under a
presupposed condition, would be false if it rested only on an
arbitrary subjective necessity, implanted in us, of connecting
certain empirical representations according to the rule of
causal relation. I would not then be able to say that the effect
is connected with the cause in the object, that is to say, neces-
sarily, but only that I am so constituted that I cannot think
this representation otherwise than as thus connected. This is
exactly what the sceptic most desires. For if this be the situa-
tion, all our insight, resting on the supposed objective validity
of our judgments, is nothing but sheer illusion; nor would
there be wanting people who would refuse to admit this sub-
jective necessity, a necessity which can only be felt. Certainly
a man cannot dispute with anyone regarding that which de-
pends merely on the mode in which he is himself organised. 
Brief Outline of this Deduction 
The deduction is the exposition of the pure concepts of the
understanding, and therewith of all theoretical a priori know-
ledge, as principles of the possibility of experience -- the prin-
ciples being here taken as the determination of appearances in
space and time in general, and this determination, in turn, as
ultimately following from the original synthetic unity of apper-
ception, as the form of the understanding in its relation to
space and time, the original forms of sensibility. 
I consider the division by numbered paragraphs as neces-
sary up to this point, because thus far we have had to treat
of the elementary concepts. We have now to give an account
of their employment, and the exposition may therefore pro-
ceed in continuous fashion, without such numbering.