concepts.

  Now a division of the complex of all the objects to which those
concepts are referred for the purpose, where possible, of compassing
their knowledge, may be made according to the varied competence or
incompetence of our faculty in that connection.

  Concepts, so far as they are referred to objects apart from the
question of whether knowledge of them is possible or not, have their
field, which is determined simply by the relation in which their
object stands to our faculty of cognition in general. The part of this
field in which knowledge is possible for us is a territory
(territorium) for these concepts and the requisite cognitive
faculty. The part of the territory over which they exercise
legislative authority is the realm (ditio) of these concepts, and
their appropriate cognitive faculty. Empirical concepts have,
therefore, their territory, doubtless, in nature as the complex of all
sensible objects, but they have no realm (only a dwelling-place,
domicilium), for, although they are formed according to law, they
are not themselves legislative, but the rules founded on them are
empirical and, consequently, contingent.

  Our entire faculty of cognition has two realms, that of natural
concepts and that of the concept of freedom, for through both it
prescribes laws a priori. In accordance with this distinction, then,
philosophy is divisible into theoretical and practical. But the
territory upon which its realm is established, and over which it
exercises its legislative authority, is still always confined to the
complex of the objects of all possible experience, taken as no more
than mere phenomena, for otherwise legislation by the understanding in
respect of them is unthinkable.

  The function of prescribing laws by means of concepts of nature is
discharged by understanding and is theoretical. That of prescribing
laws by means of the concept of freedom is discharged by reason and is
merely practical. It is only in the practical sphere that reason can
prescribe laws; in respect of theoretical knowledge (of nature) it can
only (as by the understanding advised in the law) deduce from given
logical consequences, which still always remain restricted to
nature. But we cannot reverse this and say that where rules are
practical reason is then and there legislative, since the rules
might be technically practical.

  Understanding and reason, therefore, have two distinct jurisdictions
over one and the same territory of experience. But neither can
interfere with the other. For the concept of freedom just as little
disturbs the legislation of nature, as the concept of nature
influences legislation through the concept of freedom. That it is
possible for us at least to think without contradiction of both
these jurisdictions, and their appropriate faculties, as co-existing
in the same subject, was shown by the Critique of Pure Reason, since
it disposed of the objections on the other side by detecting their
dialectical illusion.

  Still, how does it happen that these two different realms do not
form one realm, seeing that, while they do not limit each other in
their legislation, they continually do so in their effects in the
sensible world? The explanation lies in the fact that the concept of
nature represents its objects in intuition doubtless, yet not as
things in-themselves, but as mere phenomena, whereas the concept of
freedom represents in its object what is no doubt a thing-in-itself,
but it does not make it intuitable, and further that neither the one
nor the other is capable, therefore, of furnishing a theoretical
cognition of its object (or even of the thinking subject) as a
thing-in-itself, or, as this would be, of the supersensible idea of
which has certainly to be introduced as the basis of the possibility
of all those objects of experience, although it cannot itself ever
be elevated or extended into a cognition.

  Our entire cognitive faculty is, therefore, presented with an
unbounded, but, also, inaccessible field-the field of the
supersensible-in which we seek in vain for a territory, and on
which, therefore, we can have no realm for theoretical cognition, be
it for concepts of understanding or of reason. This field we must
indeed occupy with ideas in the interest as well of the theoretical as
the practical employment of reason, but, in connection with the laws
arising from the concept of freedom, we cannot procure for these ideas
any but practical reality, which, accordingly, fails to advance our
theoretical cognition one step towards the supersensible.

  Albeit, then, between the realm of the natural concept, as the
sensible, and the realm of the concept of freedom, as the
supersensible, there is a great gulf fixed, so that it is not possible
to pass from the to the latter (by means of the theoretical employment
of reason), just as if they were so many separate worlds, the first of
which is powerless to exercise influence on the second: still the
latter is meant to influence the former-that is to say, the concept of
freedom is meant to actualize in the sensible world the end proposed
by its laws; and nature must consequently also be capable of being
regarded in such a way that in the conformity to law of its form it at
least harmonizes with the possibility of the ends to be effectuated in
it according to the laws of freedom. There must, therefore, be a
ground of the unity of the supersensible that lies at the basis of
nature, with what the concept of freedom contains in a practical
way, and although the concept of this ground neither theoretically nor
practically attains to a knowledge of it, and so has no peculiar realm
of its own, still it renders possible the transition from the mode
of thought according to the principles of the one to that according to
the principles of the other.