The direct opposite of the principle of morality is, when the
principle of private happiness is made the determining principle of
the will, and with this is to be reckoned, as I have shown above,
everything that places the determining principle which is to serve
as a law, anywhere but in the legislative form of the maxim. This
contradiction, however, is not merely logical, like that which would
arise between rules empirically conditioned, if they were raised to
the rank of necessary principles of cognition, but is practical, and
would ruin morality altogether were not the voice of reason in
reference to the will so clear, so irrepressible, so distinctly
audible, even to the commonest men. It can only, indeed, be maintained
in the perplexing speculations of the schools, which are bold enough
to shut their ears against that heavenly voice, in order to support
a theory that costs no trouble.

Suppose that an acquaintance whom you otherwise liked were to
attempt to justify himself to you for having borne false witness,
first by alleging the, in his view, sacred duty of consulting his
own happiness; then by enumerating the advantages which he had
gained thereby, pointing out the prudence he had shown in securing
himself against detection, even by yourself, to whom he now reveals
the secret, only in order that he may be able to deny it at any
time; and suppose he were then to affirm, in all seriousness, that
he has fulfilled a true human duty; you would either laugh in his
face, or shrink back from him with disgust; and yet, if a man has
regulated his principles of action solely with a view to his own
advantage, you would have nothing whatever to object against this mode