itself, but that there is more beyond it; but this something more I
know no further. Of pure reason which frames this ideal, there remains
after the abstraction of all matter, i.e., knowledge of objects,
nothing but the form, namely, the practical law of the universality of
the maxims, and in conformity with this conception of reason in
reference to a pure world of understanding as a possible efficient
cause, that is a cause determining the will. There must here be a
total absence of springs; unless this idea of an intelligible world is
itself the spring, or that in which reason primarily takes an
interest; but to make this intelligible is precisely the problem
that we cannot solve.

Here now is the extreme limit of all moral inquiry, and it is of
great importance to determine it even on this account, in order that
reason may not on the one band, to the prejudice of morals, seek about
in the world of sense for the supreme motive and an interest
comprehensible but empirical; and on the other hand, that it may not
impotently flap its wings without being able to move in the (for it)
empty space of transcendent concepts which we call the intelligible
world, and so lose itself amidst chimeras. For the rest, the idea of a
pure world of understanding as a system of all intelligences, and to
which we ourselves as rational beings belong (although we are likewise
on the other side members of the sensible world), this remains
always a useful and legitimate idea for the purposes of rational
belief, although all knowledge stops at its threshold, useful, namely,
to produce in us a lively interest in the moral law by means of the
noble ideal of a universal kingdom of ends in themselves (rational
beings), to which we can belong as members then only when we carefully
conduct ourselves according to the maxims of freedom as if they were
laws of nature.