TRANSCENDENTAL DEDUCTION OF THE PURE CONCEPTS
OF THE UNDERSTANDING (B) (Selections)
$15
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 B130
faculty of representation; and since this faculty, to distinguish
it from sensibility, must be entitled understanding, all
combination -- 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
cannot be given through objects. Being an act of the self-
activity of the subject, it cannot be executed save by the subject
itself. It will easily be observed that this action is originally
one and is equipollent for all combination, and that is
dissolution, 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 concept
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 B131
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 combination.
This unity, which precedes a priori all concepts of combination,
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 therefore
of the possibility of the understanding, even as regards
its logical employment.
$16
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
in me which could not be thought at all, and that is equivalent B132
to saying that the representation would be impossible, or at
least would be nothing to me.
 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
distinguished from the consciousness of the other; and it is with the
synthesis of this (possible) consciousness that we are here alone
concerned. 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-consiousness
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
representation. 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 representations
(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 B133
me. From this original combination many consequences
follow.
 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 consciousness
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
representation with consciousness, but only in so far as I conjoin
one representation with another, and am conscious of the
synthesis 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
consciousness in [i.e. throughout] these representations. In other
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 B134
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
presupposes 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
otherwise I should have as many-coloured and diverse a self as I
have representations of which I am conscious to myself.
Synthetic 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. Combination
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 B135
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
itself, indeed, an identical, and therefore analytic, proposition;
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 consciousness
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
constituting one intuition. This amounts to saying, that I am
conscious to myself a priori of a necessary synthesis of
representations -- 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. B136
$17
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 principle
of the same possibility, in its relation to understanding,
is that all the manifold of intuition should be subject to
conditions of the original synthetic unity of apperception.
 In so 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 B137
nothing can be thought or known, since the given
representations would not have in common the act of the
apperception 'I think', and so could not be apprehended together in
knowledge. This knowledge consists in the determinate relation
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 knowledge;
and upon it therefore rests the very possibility of the
understanding.
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
knowledge. To know anything in space (for instance, a line), I
must draw it, and thus synthetically bring into being a  B138
determinate 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
consciousness 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
synthesis, the manifold would not be united in one
consciousness.
Although this proposition makes synthetic unity a condition
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
representations, and so can comprehend them as synthetically
combined 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 understanding
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 manifold
of intuition -- an understanding, that is to say, through B139
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 intuition
which is different in kind from that in space and time.
...
$19
The Logical Form of all Judgments consists in the Objective
Unity of the Apperception of the Concepts which they
contain
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 B141
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.
 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
according 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 B142
the objective unity of given representations from the subjective.
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 objective
determination of all representations, in so far as knowledge
can be acquired by means of these representations --
principles which are all derived from the fundamental principle
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.

$20 B143
All Sensible Intuitions are subject to the Categories, as
Conditions under which alone their Manifold can come
together in one Consciousness
The manifold given in a sensible intuition is necessarily
subject to the original synthetic unity of apperception, because
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
categories.