FOUNDATIONS OF THEMETAPHYSICS OFMORALS 893
Thus the question How is a categorical imperative possible?can be answered
to this extent: We can cite the only presupposition under which it is possible. This is
the Idea of freedom, and we can have insight into the necessity of this presupposition
which is sufficient to the practical use of reason (i.e., to the conviction of the validity
of this imperative and hence also of the moral law). But how this presupposition itself
is possible can never be discerned by any human reason. However, on the presupposi-
tion of freedom of the will as an intelligence, its autonomy as the formal condition
under which alone it can be determined is a necessary consequence. To presuppose
the freedom of the will is not only quite possible, as speculative philosophy itself can
prove, for it does not involve itself in a contradiction with the principle of natural
necessity in the interconnection of appearances in the world of sense. But it is also
unconditionally necessary that a rational being conscious of its causality through rea-
son, and thus conscious of a will different from desires, should practically presuppose
freedom (i.e., presuppose it in the Idea as the fundamental condition of all his volun-
tary acts). Yet how pure reason, without any other incentives whencesoever derived,
can by itself be practical (i.e., how the simple principle of the universal validity of its
maxims as laws—which would certainly be the form of a pure practical reason—
without any material (object) of the will in which we might in advance take some
interest), and can itself furnish an incentive and produce an interest which would be
called purely moral; or, in other words,how pure reason can be practical—to explain
this, all human reason is wholly incompetent, and all the pain and work of seeking an
explanation of it are wasted.
It is just the same as if I sought to find out how freedom itself as the causality of a
will is possible, for in so doing I would leave the philosophical basis of explanation
behind, and I have no other. Certainly I could revel in the intelligible world, the world
of intelligences, which still remains to me; but although I have a well-founded Idea of
it, still I do not have the least knowledge of it, nor can I ever attain knowledge of it by
all the exertions of my natural faculty of reason. This intelligible world signifies only a
something which remains when I have excluded from the determining grounds of my
will everything belonging to the world of sense, in order to isolate the principle of
motives from the field of sensibility. I do so by limiting it and showing that it does not
contain absolutely everything in itself but that outside it there is still more; but this more
I do not know. After banishing all material (i.e., knowledge of objects) from pure reason
which formulates this ideal, there remain to me only the form, the practical law of the
universal validity of maxims, and, in accordance with this, reason in relation to a pure
intelligible world as a possible efficient cause determining the will. Any incentive must
here be totally absent unless this Idea of an intelligible world or that in which reason
directly takes an interest be the incentive. But to make this conceivable is precisely the
problem we cannot solve.
Here, then, is the outermost boundary of all moral inquiry. To define it is very impor-
tant, both in order that reason may not seek around, on the one hand, in the world of sense,
in a way harmful to morals, for the supreme motive and for a comprehensible but empirical
interest; and so that it will not, on the other hand, impotently flap its wings in the space (for
it, an empty space) of transcendent concepts which we call the intelligible world, without
being able to move from its starting point and so losing itself amid phantoms. Furthermore,
the Idea of a pure intelligible world as a whole of all intelligences to which we ourselves
belong as rational beings (though on the other side we are at the same time members of the
world of sense) is always a useful and permissible Idea for the purpose of a rational faith.
This is so even though all knowledge terminates at its boundary, for the glorious ideal of a
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