ion anterior to objects, space must be only the[40] form
of sensibility.

[40] _The_ and not _a_, because, for the moment, time is
ignored.

Now why does Kant think that this conclusion follows? Before we can
answer this question we must remove an initial difficulty. In this
passage Kant unquestionably identifies a form of perception with an
actual perception. It is at once an actual perception and a capacity
of perceiving. This is evident from the words, "It is possible only in
one way for my perception to precede the actuality of the object ...
viz. _if it contains nothing but the form of the sensibility_."[41]
The identification becomes more explicit a little later. "A pure
perception (of space and time) can underlie the empirical perception
of objects, because it is nothing but the mere form of the
sensibility, which precedes the actual appearance of the objects, in
that it in fact first makes them possible. Yet this faculty of
perceiving _a priori_ affects not the matter of the phenomenon, i. e.
that in it which is sensation, for this constitutes that which is
empirical, but only its form, viz. space and time."[42] His argument,
however, can be successfully stated without this identification. It is
only necessary to re-write his cardinal assertion in the form 'the
perception of space must be nothing but the _manifestation_ of the
form of the sensibility'. Given this modification, the question
becomes, 'Why does Kant think that the perception of empty space,
involved by geometrical judgements, can be only a manifestation of our
perceiving nature, and not in any way the apprehension of a real
quality of objects?' The answer must be that it is because he thinks
that, while in empirical perception a real object is present, in the
perception of empty space a real object is not present. He regards
this as proving that the latter perception is only of something
subjective or mental. "Space and time, by being pure _a priori_
perceptions, prove that they are mere forms of our sensibility which
must precede all empirical perception, i. e. sense-perception of
actual objects."[43] His main conclusion now follows easily enough. If
in perceiving empty space we are only apprehending a manifestation of
our perceiving nature, what we apprehend in a geometrical judgement is
really a law of our perceiving nature, and therefore, while it _must_
apply to our perceptions of objects or to objects as perceived, it
_cannot_ appl