of the sensibility; it would be folly to enjoin by a moral law
that which everyone does of himself, and does superabundantly. Moreover,
the theories of the social inclinations and of moral sense fail of their
purpose, since they base morality on the uncertain ground of feeling. Even
the principle of perfection proves insufficient, inasmuch as it limits the
individual to himself, and, in the end, like those which have preceded,
amounts to a refined self-love. Theonomic ethics, egoistic ethics, the
ethics of sympathy, and the ethics of perfection are all eudemonistic, and
hence heteronomic. The practical reason[1] receives the law neither from
the will of God nor from natural impulse, but draws it out of its own
depths; it binds itself.

[Footnote 1: Will and practical reason are identical. The definition runs:
Will is the faculty of acting in accordance with the representation of
laws.]

The grounds which establish the derivation of the moral law from the will
or reason itself exclude at the same time every material determination of
it. If the categorical imperative posited definite ends for the will, if it
prescribed a direction to definite objects, it could neither be known _a
priori_ nor be valid for all rational beings: its apodictic character
forbids the admission of empirical elements of every sort.[1] If we think
away all content from the law we retain the form of universal legality,[2]
and gain the formula: "Act so that the maxim of thy will can always at
the same time hold good as a principle of universal legislation." The
possibility of conceiving the principle of volition as a universal law of
nature is the criterion of morality. If you are in doubt concerning the
moral character of an action or motive simply ask yourself the question,
What would become of humanity if everyone were to act according to the same
principle? If no one could trust the word of another, or count on aid from
others, or be sure of his property and his life, then no social life would
be possible. Even a band of robbers cannot exist unless certain laws are
respected as inviolable duties.

[Footnote 1: The moral law, therefore, is independent of all experience in
three respects, as to its origin, its content, and its validity. It springs
from reason, it contains a formal precept only, and its validity is not
concerned, whether it meets with obedience or not. It declares what ought
to be done, even though this never should be done.]

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