istics of an object
anterior to the actual presence of the object in perception.[45] This
implies that _empirical_ perception, which involves the actual
presence of the object, involves no difficulty; in other words, it is
implied that empirical perception is of objects as they are. And we
find Kant admitting this to the extent of allowing _for the sake of
argument_ that the perception of a present thing can make us know the
thing as it is in itself.[46] But if empirical perception gives us
things as they are, and if, as is the case, and as Kant really
presupposes, the objects of empirical perception are spatial, then,
since space is their form, the judgements of geometry must relate to
things as they are. It is true that on this view Kant's first
presupposition of geometrical judgements has to be stated by saying
that we are able to perceive a real characteristic of things in space,
before we perceive the things; and, no doubt, Kant thinks this
impossible. According to him, when we perceive empty space no object
is present, and therefore what is before the mind must be merely
mental. But no greater difficulty is involved than that involved in
the corresponding supposition required by Kant's own view. It is
really just as difficult to hold that we can perceive a characteristic
of things as they appear to us _before_ they appear, as to hold that
we can perceive a characteristic of them as they are in themselves
_before_ we perceive them.

[45] Cf. _Prol._, Section 8.

[46] _Prol._, Sec. 9 (cf. p. 55).

The fact is that the real difficulty with which Kant is grappling in
the _Prolegomena_ arises, not from the supposition that spatial bodies
are things in themselves, but from the supposed presupposition of
geometry that we must be able to perceive empty space before we
perceive bodies in it. It is, of course, impossible to defend the
perception of empty space, but _if_ it be maintained, the space
perceived must be conceded to be not, as Kant thinks, something mental
or subjective, but a real characteristic of things. For, as has been
pointed out, the paradox of pure perception is reached solely through
the consideration that, while in empirical perception we perceive
objects, in pure perception we do not, and since the objects of
empirical perception are spatial, space must be a real characteristic
of them.

The general result of the preceding criticism is that Kant's
conclusion does not follow from the premi