The argument follows the strict, rigorous, synthetic method. From the
already demonstrated _a priori_ character of space, Kant deduces the
apodictic certainty of all geometrical principles. But though the
paragraph thus expounds a consequence that follows from the _a priori_
character of space, not an argument in support of it, something in the
nature of an argument is none the less implied. The fact that this view
of the representation of space alone renders mathematical science
possible can be taken as confirming this interpretation of its nature.
Such an argument, though circular, is none the less cogent.
Consideration of Kant’s further statements, that were space known in a
merely empirical manner we could not be sure that in all cases only one
straight line is possible between two points, or that space will always
be found to have three dimensions, must meantime be deferred.[455]
In the new transcendental exposition Kant adopts the analytic method of
the _Prolegomena_, and accordingly presents his argument in independence
of the results already established. He starts from the assumption of the
admitted validity of geometry, as being a body of synthetic _a priori_
knowledge. Yet this, as we have already noted, does not invalidate the
argument; in both the first and the last paragraphs it is implied that
the _a priori_ and intuitive characteristics of space have already been
proved. From the synthetic character of geometrical propositions Kant
argues[456] that space must be an intuition. Through pure concepts no
synthetic knowledge is possible. Then from the apodictic character of
geometry he infers that space exists in us as pure and _a priori_;[457]
no experience can ever reveal necessity. But geometry also exists as an
applied science; and to account for our power of anticipating
experience, we must view space as existing only in the perceiving
subject as the form of its sensibility. If it precedes objects as the
necessary subjective condition of their apprehension, we can to that
extent predetermine the conditions of their existence.