properly
constitutes the Imperative necessary. The Imperative is thus single,
and runs: _Act according to that maxim only which you can wish at the
same time to become a_ _universal law_. Or, since universality of law
as determining effects is what we understand by nature: _Act as if the
maxim of your action ought by your will to become the universal law of
nature_.

Taking cases of duties according to the common divisions of duties to
ourselves and to others, perfect and imperfect, he proceeds to show
that they may be all deduced from the single Imperative; the question
of the _reality_ of duty, which is the same as the establishment of the
possibility of the Imperative as a synthetic practical proposition _a
priori_, at present altogether apart. Suppose a man tempted to commit
suicide, with the view of bettering his evil condition; but it is
contradictory that the very principle of self-conservation should lead
to self-destruction, and such a maxim of conduct cannot therefore
become a universal law of nature. Next, the case of a man borrowing
without meaning to repay, has only to be turned into a universal law,
and the thing becomes impossible; nobody would lend. Again, to neglect
a talent that is generally useful for mere ease and self-gratification,
can indeed be supposed a universal practice, but can never be wished to
be. Finally, to refuse help to others universally might not ruin the
race, but can be wished by no one that knows how soon he must himself
need assistance. Now, the rule was, that a maxim of conduct should be
_wished_ to become the universal law. In the last two cases, it cannot
be wished; in the others, the maxim cannot even be conceived in
universal form. Thus, two grades of duty, one admitting of merit, the
other so strict as to be irremissible, are established on the general
principle. The principle is moreover confirmed in the case of
transgression of duty: the transgressor by no means wishes to have his
act turned into a general rule, but only seeks special and temporary
exemption from a law allowed by himself to be universal.

Notwithstanding this force and ease of application, a categorical
Imperative has not yet been proved _a priori_ actually existent; and it
was allowed that it could not be proved empirically, elements of
inclination, interest, &c., being inconsistent with morality. The real
question is this: Is it a necessary law that all rational beings should
act on maxims that they c