ived succession in time. This
doubt (without the hasty conclusions), says Kant, must be generalized, must
be extended to the category of substance (which had been already done by
Hume, pp. 226-7, though the author of the Critique of Reason was not aware
of the fact), and to all other pure concepts of the understanding. Then we
may hope to kindle a torch at the spark which Hume struck out. The problem
"It is impossible to see why, because something exists, something else must
necessarily exist," is the starting point alike of Hume's skepticism and
Kant's criticism. The former recognized that the principle of causality
is neither empirical nor analytic, and therefore concluded that it is an
invention of reason, which confuses subjective with objective necessity.
The latter shows that in spite of its subjective origin it has an objective
value; that it is a truth which is independent of all experience, and yet
valid for all who have experience, and for all that can be experienced.

Of the two questions, "How can the concepts which spring from our
understanding possess objective validity?" and, "How (through what means
or media) does their application to objects of experience take place?"
the first is answered in the Deduction of the Pure Concepts of the
Understanding, and the second in the chapter on their Schematism.

The _Deduction_, the most difficult portion of the Critique, shows that the
objective validity of the categories, as concepts of objects in general,
depends on the fact that _through them alone experience_ as far as regards
the form of thought _is possible, _i.e._, it is only through them that any
object whatever can be thought. All knowledge consists in judgments; all
judgments contain a connection of representations; all connection--whether
it be conscious or not, whether it relates to concepts or to pure or
empirical intuitions--is an _act of the understanding_; it cannot be given
by objects, but only spontaneously performed by the subject itself. We
cannot represent anything as connected in the object unless we have
ourselves first connected it. The connection includes three conceptions:
that of the manifold to be connected (which is given by intuition), that
of the act of synthesis, and that of the unity; this last is two-fold,
an objective unity (the conception of an object in general in which the
manifold is united), and a subjective unity (the unity of consciousness
under which or, rather, through whi