In theory, Kant states, a man deserves moral credit for an action done from
duty, even if his inclinations also favor it—but only insofar as the latter
are incidental and play no role in his motivation. But in practice, Kant
maintains, whenever the two coincide no one can know that he has escaped the
influence of inclination. For all practical purposes, therefore, a moral man
must have no private stake in the outcome of his actions, no personal motive,
no expectation of profit or gain of any kind.
Even then, however, he cannot be sure that no fragment of desire is “secretly”
moving him. The far clearer case, the one case in which a man can at least come
close to knowing that he is moral, occurs when the man’s desires clash with
his duty and he acts in defiance of his desires.