If we have hitherto drawn our notion of duty from the common use
of our practical reason, it is by no means to be inferred that we have
treated it as an empirical notion. On the contrary, if we attend to
the experience of men's conduct, we meet frequent and, as we ourselves
allow, just complaints that one cannot find a single certain example
of the disposition to act from pure duty. Although many things are
done in conformity with what duty prescribes, it is nevertheless
always doubtful whether they are done strictly from duty, so as to
have a moral worth. Hence there have at all times been philosophers
who have altogether denied that this disposition actually exists at
all in human actions, and have ascribed everything to a more or less
refined self-love. Not that they have on that account questioned the
soundness of the conception of morality; on the contrary, they spoke
with sincere regret of the frailty and corruption of human nature,
which, though noble enough to take its rule an idea so worthy of
respect, is yet weak to follow it and employs reason which ought to
give it the law only for the purpose of providing for the interest
of the inclinations, whether singly or at the best in the greatest
possible harmony with one another.

In fact, it is absolutely impossible to make out by experience
with complete certainty a single case in which the maxim of an action,
however right in itself, rested simply on moral grounds and on the
conception of duty. Sometimes it happens that with the sharpest
self-examination we can find nothing beside the moral principle of
duty which could have been powerful enough to move us to this or
that action and to so great a sacrifice; yet we cannot from this infer