SS 22.
Transcendental Deduction of the universally possible employment
in experience of the Pure Conceptions of the Understanding.
In the metaphysical deduction, the a priori origin of categories was
proved by their complete accordance with the general logical of
thought; in the transcendental deduction was exhibited the possibility
of the categories as a priori cognitions of objects of an intuition in
general (SS 16 and 17).At present we are about to explain the
possibility of cognizing, a priori, by means of the categories, all
objects which can possibly be presented to our senses, not, indeed,
according to the form of their intuition, but according to the
laws of
their conjunction or synthesis, and thus, as it were, of prescribing
laws to nature and even of rendering nature possible. For if the
categories were inadequate to this task, it would not be evident to us
why everything that is presented to our senses must be subject to
those laws which have an
a priori origin in the understanding itself.
I premise that by the term synthesis of apprehension, I understand
the combination of the manifold in an empirical intuition, whereby
perception, that is, empirical consciousness of the intuition (as
phenomenon), is possible.
We have a priori forms of the external and internal sensuous
intuition in the representations of space and time, and to these
must the synthesis of apprehension of the manifold in a phenomenon
be always comformable, because the synthesis itself can only take
place according to these forms. But space and time are not merely
forms of sensuous intuition, but intuitions themselves (which
contain a manifold), and therefore contain a priori the
determination of the unity of this manifold.* (See the Trans.
Aesthetic.) Therefore is unity of the synthesis of the manifold
without or within us, consequently also a conjunction to which all
that is to be represented as determined in space or time must
correspond, given a priori along with (not in) these intuitions, as
the condition of the synthesis of all apprehension of them. But this
synthetical unity can be no other than that of the conjunction of
the manifold of a given intuition in general, in a primitive act of
consciousness, according to the categories, but applied to our
sensuous intuition. Consequently all synthesis, whereby alone is
even perception possible, is subject to the categories. And, as
experience
is cognition by means of conjoined perceptions, the
categories are conditions of the possibility of experience and are
therefore valid
a priori for all objects of experience.
[*]
Space represented as an object (as geometry really requires it to
be) contains more than the mere form of the intuition; namely, a
combination of the manifold given according to the form of sensibility
into a representation that can be intuited; so that the form of the
intuition gives us merely the manifold, but the formal intuition gives
unity of representation. In the Æsthetic, I regarded this unity as
belonging entirely to sensibility, for the purpose of indicating
that it antecedes all conceptions, although it presupposes a synthesis
which does not belong to sense, through which alone, however, all
our conceptions of space and time are possible. For as by means of
this unity alone (the understanding determining the sensibility) space
and time are given as intuitions, it follows that the unity of this
intuition a priori belongs to space and time, and not to the
conception of the understanding (SS 20).
When, then, for example, I make the empirical intuition of a house
by apprehension of the manifold contained therein into a perception,
the necessary unity of space and of my external sensuous intuition
lies at the foundation of this act, and I, as it were, draw the form
of the house conformably to this synthetical unity of the manifold
in space. But this very synthetical unity remains, even when I
abstract the form of space, and has its seat in the understanding, and
is in fact the category of the synthesis of the homogeneous in an
intuition; that is to say, the category of quantity, to which the
aforesaid synthesis of apprehension, that is, the perception, must
be completely conformable.*
[*]
In this manner it is proved, that the synthesis of apprehension,
which is empirical, must necessarily be conformable to the synthesis
of apperception, which is intellectual, and contained a priori in
the category. It is one and the same spontaneity which at one time,
under the name of imagination, at another under that of understanding,
produces conjunction in the manifold of intuition.
To take another example, when I perceive the freezing of water, I
apprehend two states (fluidity and solidity), which, as such, stand
toward each other mutually in a relation of time. But in the time,
which I place as an internal intuition, at the foundation of this
phenomenon, I represent to myself synthetical unity of the manifold,
without which the aforesaid relation could not be given in an
intuition as determined (in regard to the succession of time). Now
this synthetical unity, as the a priori condition under which I
conjoin the manifold of an intuition, is, if I make abstraction of the
permanent form of my internal intuition (that is to say, of time), the
category of cause, by means of which, when applied to my
sensibility, I determine everything that occurs according to relations
of time. Consequently apprehension in such an event, and the event
itself, as far as regards the possibility of its perception, stands
under the conception of the relation of cause and effect: and so in
all other cases.
Categories are conceptions which prescribe laws a priori to
phenomena, consequently to nature as the complex of all phenomena
(
natura materialiter spectata). And now the question arises—
inasmuch as these categories are not derived from nature, and do not
regulate themselves according to her as their model (for in that
case they would be empirical)— how it is conceivable that nature
must regulate herself according to them, in other words, how the
categories can determine
a priori the synthesis of the manifold of
nature, and yet not derive their origin from her. The following is the
solution of this enigma.
It is not in the least more difficult to conceive how the laws of
the phenomena of nature must harmonize with the understanding and with
its a priori form— that is, its faculty of conjoining the manifold—
than it is to understand how the phenomena themselves must
correspond with the a priori form of our sensuous intuition. For
laws do not exist in the phenomena any more than the phenomena exist
as things in themselves. Laws do not exist except by relation to the
subject in which the phenomena inhere, in so far as it possesses
understanding, just as phenomena have no existence except by
relation to the same existing subject in so far as it has senses. To
things as things in themselves, conformability to law must necessarily
belong independently of an understanding to cognize them. But
phenomena are only representations of things which are utterly unknown
in respect to what they are in themselves. But as mere
representations, they stand under no law of conjunction except that
which the conjoining faculty prescribes. Now that which conjoins the
manifold of sensuous intuition is imagination, a mental act to which
understanding contributes unity of intellectual synthesis, and
sensibility, manifoldness of apprehension. Now as all possible
perception depends on the synthesis of apprehension, and this
empirical synthesis itself on the transcendental, consequently on
the categories, it is evident that all possible perceptions, and
therefore everything that can attain to empirical consciousness,
that is, all phenomena of nature, must, as regards their
conjunction, be subject to the categories. And nature (considered
merely as nature in general) is dependent on them. as the original
ground of her necessary conformability to law (as natura formaliter
spectata). But the pure faculty (of the understanding) of
prescribing laws
a priori to phenomena by means of mere categories, is
not competent to enounce other or more laws than those on which a
nature in general, as a conformability to law of phenomena of space
and time, depends. Particular laws, inasmuch as they concern
empirically determined phenomena, cannot be entirely deduced from pure
laws, although they all stand under them. Experience must be
superadded in order to know these particular laws; but in regard to
experience in general, and everything that can be cognized as an
object thereof, these
a priori laws are our only rule and guide.