n this sense is object of perception.

The aim of the arguments just considered, and stated in Sec. 2 of
the _Aesthetic_, is to establish the two characteristics of our
apprehension of space,[26] from which it is to follow that space is a
property of things only as they appear to us and not as they are in
themselves. This conclusion is drawn in Sec. 4. Secs. 2 and 4 therefore
complete the argument. Sec. 3, a passage added in the second edition
of the _Critique_, interrupts the thought, for ignoring Sec. 2, it once
more establishes the _a priori_ and perceptive character of our
apprehension of space, and independently draws the conclusion drawn in
Sec. 4. Since, however, Kant draws the final conclusion in the same way
in Sec. 3 and in Sec. 4, and since a passage in the _Prolegomena_,[27]
of which Sec. 3 is only a summary, gives a more detailed account of
Kant's thought, attention should be concentrated on Sec. 3, together
with the passage in the _Prolegomena_.

[26] viz. that it is _a priori_ and a pure perception.

[27] Secs. 6-11.

It might seem at the outset that since the arguments upon which Kant
bases the premises for his final argument have turned out invalid, the
final argument itself need not be considered. The argument, however,
of Sec. 3 ignores the preceding arguments for the _a priori_ and
perceptive character of our apprehension of space. It returns to the
_a priori_ synthetic character of geometrical judgements, upon which
stress is laid in the Introduction, and appeals to this as the
justification of the _a priori_ and perceptive character of our
apprehension of space.

The argument of Sec. 3 runs as follows: "Geometry is a science which
determines the properties of space synthetically and yet _a priori_.
What, then, must be the representation of space, in order that such a
knowledge of it may be possible? It must be originally perception, for
from a mere conception no propositions can be deduced which go beyond
the conception, and yet this happens in geometry. But this perception
must be _a priori_, i. e. it must occur in us before all
sense-perception of an object, and therefore must be pure, not
empirical perception. For geometrical propositions are always
apodeictic, i. e. bound up with the consciousness of their necessity
(e. g. space has only three dimensions), and such propositions cannot
be empirical judgements nor conclusions from them."

"Now how can there exist in the mind an ext