Critique of Pure Reason (Transcendental Deduction -A)

Immanuel Kant's
Critique
trans. by Norman Kemp Smith
P 120
ANALYTIC OF CONCEPTS
CHAPTER II
THE DEDUCTION OF THE PURE CONCEPTS OF
UNDERSTANDING
Section 1
$13
THE PRINCIPLES OF ANY TRANSCENDENTAL DEDUCTION
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 
believe ourselves, even without a deduction, to be justified in 
appropriating 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 
indulgence, are yet from time to time challenged by the question:
quid juris. This demand for a deduction involves us in considerable
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 
independence of all experience; and their right to be so 
employed 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 concepts
of space and time as forms of sensibility, and the categories
as concepts of understanding. To seek an empirical deduction
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 existence.
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 
undoubtedly of great service. We are indebted to the celebrated
P 122
Locke for opening out this new line of enquiry. But a deduction
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 derivation
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 transcendental,
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 
knowledge. 
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 deduction
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 
appearances 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 
regularity among appearances and so affords abundant opportunity
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 completely
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 something
else, B, follows from it necessarily and in accordance
with an absolutely universal rule. Appearances do indeed 
present 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 
comparative universality, that is, extensive applicability. If we
were to treat pure concepts of understanding as merely 
empirical products, we should be making a complete change in
[the manner of] their employment.
$14
Transition to the Transcendental Deduction of the
Categories
There are only two possible ways in which synthetic 
representations 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 representation
possible, or the representation alone must make the
object possible. In the former case, this relation is only 
empirical, 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 knowledge
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 
intuition. 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 
antecedent conditions under which alone anything can be, if not
intuited, yet thought as object in general. In that case all 
empirical 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. 
Concepts which yield the objective ground of the possibility of
experience are for this very reason necessary. But the 
unfolding 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 
considerations, and meeting with pure concepts of the understanding
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 
experience. 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 
impossible, 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 apperception.
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 
knowledge 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 
knowledge. 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 
determined 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 
determined that its empirical intuition in experience must always
be considered as subject and never as mere predicate. 
Similarly with all the other categories.
P 129
THE DEDUCTION OF THE PURE CONCEPTS OF
UNDERSTANDING
Section 2
THE A PRIORI GROUNDS OF THE POSSIBILITY OF
EXPERIENCE
THAT a concept, although itself neither contained in the 
concept 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 intuition
corresponds to it; and intuitions in general, through which
objects can be given to us, constitute the field, the whole 
object, 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
thought.
Pure a priori concepts, if such exist, cannot indeed contain
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 
everything 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 
concept 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 necessarily
belongs to the condition of a possible experience (as in
the concept of a spirit). Or, it may be, pure concepts are 
extended 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 
experience 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; 
receptivity 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 extreme
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 
passages rather to prepare than to instruct the reader. Systematic
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 
modifications of the mind, belong to inner sense. All our 
knowledge 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 distinguishes
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 
produced only through the synthesis of the manifold which sensibility
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 become
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 
coexistence 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 imagination
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 representations,
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 
combination of the manifold such as renders a thoroughgoing
synthesis of reproduction possible, then this synthesis of 
imagination is likewise grounded, antecedently to all 
experience, 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 
necessarily 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 
particular number, obviously the various manifold representations
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 
constitutes 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 
reproductive 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 generated.
P 134
The manifold of the representation would never, therefore,
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 manifold,
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 
representation, but only with the outcome [that which is thereby
represented]. But notwithstanding these variations, such 
consciousness, however indistinct, must always be present; 
without 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 knowledge
to its object carries with it an element of necessity; the
object is viewed as that which prevents our modes of 
knowledge from being haphazard or arbitrary, and which 
determines 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 
constitutes 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 accordance
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 
therewith representations of impenetrability, shape, etc.
All necessity, without exception, is grounded in a 
transcendental condition. There must, therefore, be a transcendental
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 
perception is merely empirical, and always changing. No fixed
and abiding self can present itself in this flux of inner 
appearances. Such consciousness is usually named inner sense, or
empirical apperception. What has necessarily to be represented
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
possible.
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 apperception
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 
representations 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 transcendental
unity, thereby rendering possible their interconnection
according to a priori rules.
Now, also, we are in a position to determine more adequately
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, 
transcendental 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 concepts
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 
manifold, through a common function of the mind, which combines
it in one representation. Since this unity must be regarded
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 
P 138
interrelating 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 apperception,
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 accordance
with universal and necessary laws would be lacking, all
relation of knowledge to objects would fall away. The 
appearances 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 
intuition for that same experience. They are fundamental 
concepts 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 categories
rests on the relation in which our entire sensibility,
and with it all possible appearances, stand to original 
apperception. 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 appearances
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 understanding
from experience, and so to ascribe to them a merely empirical
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 
ourselves the thoroughgoing affinity of appearances, whereby
they stand and must stand under unchanging laws?
On my principles it is easily explicable. All possible 
appearances, as representations, belong to the totality of a 
P 140
possible self-consciousness. But as self-consciousness is a 
transcendental 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 
apprehension 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 
subjective 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 
independently 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 asserting
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
DEDUCTION OF THE PURE CONCEPTS OF
UNDERSTANDING
Section 3
THE RELATION OF THE UNDERSTANDING TO OBJECTS IN
GENERAL, AND THE POSSIBILITY OF KNOWING THEM
A PRIORI
What we have expounded separately and singly in the
preceding section, we shall now present in systematic 
interconnection. 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 apperception.
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 
empirically in perception, imagination in association (and 
reproduction), apperception in the empirical consciousness of the
identity of the reproduced representations with the 
appearances 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 thoroughgoing
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 apperception.
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 representations.
P 142
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 transcendental
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 apperception
supplies a principle of the synthetic unity of the 
manifold 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 
transcendental consciousness which precedes all special experience,
namely, the consciousness of myself as original apperception. It is
therefore absolutely necessary that in my knowledge all consciousness
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 absolutely
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 representation
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 
knowledge, 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 
represented 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 
experience 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 necessary
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 knowledge
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 
appearances, as data for a possible experience, are subject to this
understanding. This relation of appearances to possible 
experience 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 
experiences, and that appearances have a necessary relation to
the understanding.
We will now, starting from below, namely, with the empirical,
strive to make clear the necessary connection in which
understanding, by means of the categories, stands to appearances.
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, 
appearance 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 apprehension.
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 
reproductive 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 
accidental collocations; and so would not give rise to any 
knowledge. 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 reproduction
according to rules is what is called the association of
representations.
 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 combine
them so as to generate images of objects. For that purpose something
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 associable,
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 
impossible. For it is only because I ascribe all perceptions to one
consciousness (original apperception) that I can say of all 
perceptions 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 knowledge
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 apperception.
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 necessary
condition of all possible perception; and [this being recognised
we can prove that] the affinity of all appearances, near or
remote, is a necessary consequence of a synthesis in 
imagination which is grounded a priori on rules.
Since the imagination is itself a faculty of a priori synthesis,
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 
transcendental function of imagination. That the affinity of 
appearances, 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 
function no concepts would together make up a unitary
experience.
 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 
synthesis 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 apperception,
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 knowledge,
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 necessary
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 experience.
Actual experience, which is consitituted by apprehension,
association (reproduction), and finally recognition of appearances,
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 recognition,
reproduction, association, apprehension) in connection
with the appearances. For only by means of these 
fundamental 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 
subjective grounds of such unity contained a priori in the original
cognitive powers of our mind, and if these subjective conditions,
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 
definitions, when they are adequately understood, are identical.
We may now characterise it as the faculty of rules. This 
distinguishing 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 something
more than a power of formulating rules through comparison
of appearances; it is itself the lawgiver of nature.
Save through it, nature, that is, synthetic unity of the 
manifold 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 
experience. 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 
understanding. 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 
intuitions, 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 inexhaustible
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 
transcendental 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 characterised
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 precedes
all knowledge of the object as the intellectual form of
such knowledge, and itself constitutes a formal a priori knowledge
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 
apperception, 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.