secondly to discover the _a priori_ principles involved in
the categories, as exercised under these sensuous conditions, such,
for instance, as the law that all changes take place according to
the law of cause and effect. The first problem is dealt with in
the chapter on the 'schematism of the pure conceptions of the
understanding', the second in the chapter on the 'system of all
principles of the pure understanding'.

[1] p. 141.

We naturally feel a preliminary difficulty with respect to the
existence of this second part of the _Analytic_ at all. It seems clear
that if the first part is successful, the second must be unnecessary.
For if Kant is in a position to lay down that the categories must
apply to objects, no special conditions of their application need be
subsequently determined. If, for instance, it can be laid down that
the category of quantity must apply to objects, it is implied either
that there are no special conditions of its application, or that they
have already been discovered and shown to exist. Again, to assert the
applicability of the categories is really to assert the existence of
principles, and in fact of just those principles which it is the aim
of the _System of Principles_ to prove. Thus to assert the
applicability of the categories of quantity and of cause and effect is
to assert respectively the principles that all objects of perception
are extensive quantities, and that all changes take place according
to the law of cause and effect. The _Deduction of the Categories_
therefore, if successful, must have already proved the principles
now to be vindicated; and it is a matter for legitimate surprise
that we find Kant in the _System of Principles_ giving proofs of
these principles which make no appeal to the _Deduction of the
Categories_.[2] On the other hand, for the existence of the account of
the schematism of the categories Kant has a better show of reason. For
the conceptions derived in the _Metaphysical Deduction_ from the
nature of formal judgement are in themselves too abstract to be the
conceptions which are to be shown applicable to the sensible world,
since all the latter involve the thought of time. Thus, the conception
of cause and effect derived from the nature of the hypothetical
judgement includes no thought of time, while the conception of which
he wishes to show the validity is that of necessary succession in
time. Hence the conceptions discovered by analysis of formal