part from the
subject (_N.B._, the transcendental subject, concerning which more below),
they are naught. It is only from man's point of view that we can speak
of space, and of extended, moveable, changeable things; for we can know
nothing concerning the intuitions of other thinking beings, we have no
means of discovering whether they are bound by the same conditions which
limit our intuitions, and which for us are universally valid. (3) Nothing
which is intuited in space is a thing in itself. What we call external
objects are nothing but mere representations of our sensibility, whose
true correlative, the _thing in itself_, cannot be known by ever so deep
penetration into the phenomenon; such properties as belong to things in
themselves can never be given to us through the senses. Similarly nothing
that is intuited in time is a thing in itself, so that we intuit ourselves
only as we appear to ourselves, and not as we are.

The merely empirical reality of space and time, the limitation of their
validity to phenomena, leaves the certainty of knowledge within the limits
of experience intact; for we are equally certain of it, whether these forms
necessarily belong to things in themselves, or only to our intuitions
of things. The assertion of their absolute reality, on the other hand,
involves us in sheer absurdities (that is, it necessitates the assumption
of two infinite nonentities which exist, but without being anything real,
merely in order to comprehend all reality, and on one of which even our own
existence would be dependent), in view of which the origin of so peculiar
a theory as the idealism of Berkeley appears intelligible. The critical
theory of space and time is so far from being identical with, or akin to,
the theory of Berkeley, that it furnishes the best and only defense against
the latter. If anyone assumes the absolute or transcendental reality of
these forms, it is impossible for him to prevent everything, including even
our own existence, from being changed thereby into mere illusion. But
the critical philosopher is far from degrading bodies to mere illusion;
external phenomena are just as real for him as internal phenomena, though
only as phenomena, it is true, as (possible) representations.

Phenomenon and illusion are not the same. The transcendental distinction
between phenomena and things in themselves must not be confused with the
distinction common to ordinary life and to physics, in accordance wit