ses by which he supports it.
It should therefore be asked whether it is not possible to take
advantage of this hiatus by presenting the argument for the merely
phenomenal character of space without any appeal to the possibility of
perceiving empty space. For it is clear that what was primarily before
Kant, in writing the _Critique_, was the _a priori_ character of
geometrical judgements themselves, and not the existence of a
perception of empty space which they were held to presuppose.[47]

[47] The difficulty with which Kant is struggling in the
_Prolegomena_, Secs. 6-11, can be stated from a rather different
point of view by saying that the thought that geometrical
judgements imply a perception of empty space led him to apply
the term '_a priori_' to perception as well as to judgement.
The term, _a priori_, applied to judgements has a valid
meaning; it means, not that the judgement is made prior to
all experience, but that it is not based upon experience,
being originated by the mind in virtue of its own powers of
thinking. Applied to perception, however, '_a priori_' must
mean prior to all experience, and, since the object of
perception is essentially individual (cf. B. 741, M. 435),
this use of the term gives rise to the impossible task of
explaining how a perception can take place prior to the
actual experience of an individual in perception (cf.
_Prol._, Sec. 8).

If, then, the conclusion that space is only the form of sensibility
can be connected with the _a priori_ character of geometrical
judgements without presupposing the existence of a perception of empty
space, his position will be rendered more plausible.

This can be done as follows. The essential characteristic of a
geometrical judgement is not that it takes place prior to experience,
but that it is not based upon experience. Thus a judgement, arrived at
by an activity of the mind in which it remains within itself and does
not appeal to actual experience of the objects to which the judgement
relates, is implied to hold good of those objects. If the objects were
things as they are in themselves, the validity of the judgement could
not be justified, for it would involve the gratuitous assumption that
a necessity of thought is binding on things which _ex hypothesi_ are
independent of the nature of the mind. If, however, the objects in
question are things as perceived, they will be through a