fact of importance in case we should be
assured of their existence in some other way than by sensuous intuition.

The determination of the limits of speculative reason is finished.
All knowing and all demonstration is limited to phenomena or possible
experience. But the boundary of that which can be experienced is not the
boundary of that which is, still less of that which ought to be; the
boundary of theoretical reason is not the boundary of practical reason. We
_ought_ to act morally; in order to be able to do this we must ascribe to
ourselves the power to initiate a series of events; and, in general, we are
warranted in assuming everything the non-assumption of which makes moral
action impossible. If we were merely theoretical, merely experiential
beings, we should lack all occasion to suppose a second, intelligible world
behind and above the world of phenomena; but we are volitional and active
beings under laws of reason, and though we are unable to know things in
themselves, yet we may and must _postulate_ them--our freedom, God, and
immortality. For not only that which is a condition of experience is true
and necessary, but that, also, which is a condition of morality. The
discovery of the laws and conditions of morality is the mission of
practical philosophy.

%2. Theory of Ethics.%

The investigation now turns from the laws of nature, which express a
"must," to the laws of will, in which an "ought" is expressed, and by which
certain actions are not compelled, but prescribed. (If we were merely
rational, and not at the same time sensuous beings, the moral law would
determine the will in the form of a natural law; since, however, the
constant possibility of deviation is given in the sensibility, or, rather,
the moral standpoint can only be attained by conquering the sensuous
impulses, therefore the moral law speaks to us in the form of an "ought,"
of an imperative.) Among the laws of the will or imperatives, also,
there are some which possess the character of absolute necessity and
universality, and which, consequently, are _a priori_. As the understanding
dictates laws to the phenomenal world, so practical reason gives a law to
itself, is _autonomous_; and as the _a priori_ laws of nature relate only
to the form of the objects of experience, so the moral law determines not
the content, but only the form of volition: "Act only on that maxim whereby
thou canst at the same time will that it should become a unive