Accordingly, this duty to estimate the worth of one's actions not
merely by their legality, but also by their morality (mental
disposition), is only of indeterminate obligation; the law does not
command this internal action in the human mind itself, but only the
maxim of the action, namely, that we should strive with all our
power that for all dutiful actions the thought of duty should be of
itself an adequate spring.

(2) HAPPINESS OF OTHERS as an end which is also a duty

{INTRODUCTION ^paragraph 80}

(a) Physical Welfare. Benevolent wishes may be unlimited, for they
do not imply doing anything. But the case is more difficult with
benevolent action, especially when this is to be done, not from
friendly inclination (love) to others, but from duty, at the expense
of the sacrifice and mortification of many of our appetites. That this
beneficence is a duty results from this: that since our self-love
cannot be separated from the need to be loved by others (to obtain
help from them in case of necessity), we therefore make ourselves an
end for others; and this maxim can never be obligatory except by
having the specific character of a universal law, and consequently
by means of a will that we should also make others our ends. Hence the
happiness of others is an end that is also a duty.

I am only bound then to sacrifice to others a part of my welfare
without hope of recompense: because it is my duty, and it is
impossible to assign definite limits how far that may go. Much depends
on what would be the true want of each according to his own