e of the pure reason insists
that the mere form of a universal legislation must constitute the
ultimate determining principle of the will. Here is the only possible
practical principle which is sufficient to furnish categorical
imperatives, that is, practical laws which make action a duty.

It follows from this analytic that pure reason can be practical. It can
determine the will independently of all merely experimental elements.

There is a remarkable contrast between the working of the pure
speculative reason and that of the pure practical reason. In the
former--as was shown in the treatise on that subject--a pure, sensible
intuition of time and space made knowledge possible, though only of
objects of the senses.

On the contrary, the moral law brings before us a fact absolutely
inexplicable from any of the data of the world of sense. And the entire
range of our theoretical use of reason indicates a pure world of
understanding, which even positively determines it, and enables us to
know something of it--namely, a law.

We must observe the distinction between the laws of a system of nature
to which the will is subject, and of a system of nature which is subject
to the will. In the former, the objects cause the ideas which determine
the will; in the latter, the objects are caused by the will. Hence,
causality of the will has its determining principle exclusively in the
faculty of pure reason, which may, therefore, also be called a pure
practical reason.

The moral law is a law of the causality through freedom, and therefore
of the possibility of a super-sensible system of nature. It determines
the will by imposing on its maxim the condition of a universal
legislative form, and thus it is able for the first time to impart
practical reality to reason, which otherwise would continue to be
transcendent when seeking to proceed speculatively with its ideas.

Thus the moral law induces a stupendous change. It changes the
transcendent use of reason into the immanent use. And in result reason
itself becomes, by its ideas, an efficient cause in the field of
experience.

HUME AND SCEPTICISM

It may be said of David Hume that he initiated the attack on pure
reason. My own labours in the investigation of this subject were
occasioned by his sceptical teaching, for his assault made them
necessary. He argued that without experience it is impossible to know
the difference between one thing and another; that is, we can know _