that of indebtedness (officium debiti), since although another man
by virtue of his rights can demand that my actions shall conform to
the law, he cannot demand that the law shall also contain the spring
of these actions. The same thing is true of the general ethical
command, "Act dutifully from a sense of duty." To fix this disposition
firmly in one's mind and to quicken it is, as in the former case,
meritorious, because it goes beyond the law of duty in actions and
makes the law in itself the spring.

But just for or reason, those duties also must be reckoned as of
indeterminate obligation, in respect of which there exists a
subjective principle which ethically rewards them; or to bring them as
near as possible to the notion of a strict obligation, a principle
of susceptibility of this reward according to the law of virtue;
namely, a moral pleasure which goes beyond mere satisfaction with
oneself (which may be merely negative), and of which it is proudly
said that in this consciousness virtue is its own reward.

{INTRODUCTION ^paragraph 70}

When this merit is a merit of the man in respect of other men of
promoting their natural ends, which are recognized as such by all
men (making their happiness his own), we might call it the sweet
merit, the consciousness of which creates a moral enjoyment in which
men are by sympathy inclined to revel; whereas the bitter merit of
promoting the true welfare of other men, even though they should not
recognize it as such (in the case of the unthankful and ungrateful),
has commonly no such reaction, but only produces a satisfaction with
one's self, although in the latter case this would be even greater.