the thing in itself manifests to us not its nature,
indeed, but its existence. The same holds true in practical philosophy of
the moral law. The incontestable fact of the moral law empowers me to rank
myself in a higher order of things than the merely phenomenal order, and
in another causal relation than that of the merely necessary (mechanical)
causation of nature, to regard myself as a legislative member of an
intelligible world, and one independent of sensuous impulses--in short, to
regard myself as free. Freedom is the _ratio essendi_ of the self-given
moral law, the latter the _ratio cognoscendi_ of freedom. The law would
have no meaning if we did not possess the power to obey it: I can _because_
I ought. It is true that freedom is a mere Idea, whose object can never be
given to me in an experience, and whose reality, consequently, cannot
be objectively known and proved, but nevertheless, is required with
satisfactory subjective necessity as the condition of the moral law and of
the possibility of its fulfillment. I may not say it is certain, but, with
safety, I am certain that I am free. Freedom is not a dogmatic proposition
of theoretical reason, but a _postulate_ of practical reason; and the
latter holds the _primacy_ over the former to this extent, that it can
require the former to show that certain transcendent Ideas of the
suprasensible, which are most intimately connected with moral obligation,
are compatible with the principles of the understanding. It was just in
view of the practical interests involved in the rational concepts God,
freedom, immortality, that it was so important to establish, at least,
their possibility (their conceivability without contradiction). That,
therefore, which the Dialectic recognized as possible is in the Ethics
shown to be real: Whoever seeks to fulfill his moral destiny--and this is
the duty of every man--must not doubt concerning the conditions of its
possible fulfillment, must, in spite of their incomprehensibility,
_believe_ in freedom and a suprasensible world. They are both postulates
of practical reason, _i.e._, assumptions concerning that which is in behalf
of that which ought to be. Naturally the interests of the understanding
must not be infringed upon by those of the will. The principle of the
complete causal determination of events retains its validity unimpeached
for the sphere of the knowledge of the understanding, that is, for the
realm of phenomena; while, on the