But in order that in this study we may not merely advance by the
natural steps from the common moral judgement (in this case very
worthy of respect) to the philosophical, as has been already done, but
also from a popular philosophy, which goes no further than it can
reach by groping with the help of examples, to metaphysic (which
does allow itself to be checked by anything empirical and, as it
must measure the whole extent of this kind of rational knowledge, goes
as far as ideal conceptions, where even examples fail us), we must
follow and clearly describe the practical faculty of reason, from
the general rules of its determination to the point where the notion
of duty springs from it.

Everything in nature works according to laws. Rational beings
alone have the faculty of acting according to the conception of
laws, that is according to principles, i.e., have a will. Since the
deduction of actions from principles requires reason, the will is
nothing but practical reason. If reason infallibly determines the
will, then the actions of such a being which are recognised as
objectively necessary are subjectively necessary also, i.e., the
will is a faculty to choose that only which reason independent of
inclination recognises as practically necessary, i.e., as good. But if
reason of itself does not sufficiently determine the will, if the
latter is subject also to subjective conditions (particular
impulses) which do not always coincide with the objective
conditions; in a word, if the will does not in itself completely
accord with reason (which is actually the case with men), then the
actions which objectively are recognised as necessary are subjectively
contingent, and the determination of such a will according to
objective laws is obligation, that is to say, the relation of the
objective laws to a will that is not thoroughly good is conceived as