law of nature); but the subjective principle is in the end; now by the
second principle the subject of all ends is each rational being,
inasmuch as it is an end in itself. Hence follows the third
practical principle of the will, which is the ultimate condition of
its harmony with universal practical reason, viz.: the idea of the
will of every rational being as a universally legislative will.

On this principle all maxims are rejected which are inconsistent
with the will being itself universal legislator. Thus the will is
not subject simply to the law, but so subject that it must be regarded
as itself giving the law and, on this ground only, subject to the
law (of which it can regard itself as the author).

In the previous imperatives, namely, that based on the conception of
the conformity of actions to general laws, as in a physical system
of nature, and that based on the universal prerogative of rational
beings as ends in themselves- these imperatives, just because they
were conceived as categorical, excluded from any share in their
authority all admixture of any interest as a spring of action; they
were, however, only assumed to be categorical, because such an
assumption was necessary to explain the conception of duty. But we
could not prove independently that there are practical propositions
which command categorically, nor can it be proved in this section; one
thing, however, could be done, namely, to indicate in the imperative
itself, by some determinate expression, that in the case of volition
from duty all interest is renounced, which is the specific criterion
of categorical as distinguished from hypothetical imperatives. This is
done in the present (third) formula of the principle, namely, in the
idea of the will of every rational being as a universally
legislating will.