When it is said of the perfection that belongs to man generally (properly speaking, to humanity), that it is in itself a duty to make this our end, it must be placed in that which may be the effect of one’s deed, not in that which is merely an endowment for which we have to thank nature; for otherwise it would not be duty.  Consequently, it can be nothing else than the cultivation of one’s power (or natural capacity) and also of one’s will (moral disposition) to satisfy the requirement of duty in general.  The supreme element in the former (the power) is the understanding, it being the faculty of concepts, and, therefore, also of those concepts which refer to duty.  First it is his duty to labour to raise himself out of the rudeness of his nature, out of his animal nature more and more to humanity, by which alone he is capable of setting before him ends to supply the defects of his ignorance by instruction, and to correct his errors; he is not merely counselled to do this by reason as technically practical, with a view to his purposes of other kinds (as art), but reason, as morally practical, absolutely commands him to do it, and makes this end his duty, in order that he may be worthy of the humanity that dwells in him.  Secondly, to carry the cultivation of his will up to the purest virtuous disposition, that, namely, in which the law is also the spring of his dutiful actions, and to obey it from duty, for this is internal morally practical perfection.  This is called the moral sense (as it were a special sense, sensus moralis), because it is a feeling of the effect which the legislative will within himself exercises on the faculty of acting accordingly.  This is, indeed, often misused fanatically, as though (like the genius of Socrates) it preceded reason, or even could dispense with judgement of reason; but still it is a moral perfection, making every special end, which is also a duty, one’s own end.

{Introduction ^paragraph 50}

B. Happiness of others

It is inevitable for human nature that a should wish and seek for happiness, that is, satisfaction with his condition, with certainty of the continuance of this satisfaction.  But for this very reason it is not an end that is also a duty.  Some writers still make a distinction between moral and physical happiness (the former consisting in satisfaction with one’s person and moral behaviour, that is, with what one does; the other in satisfaction with that which nature confers, consequently with what one enjoys as a foreign gift).  Without at present censuring the misuse of the word (which even involves a contradiction), it must be observed that the feeling of the former belongs solely to the preceding head, namely, perfection.  For he who is to feel himself happy in the mere consciousness of his uprightness already possesses that perfection which in the previous section was defined as that end which is also duty.