367. What are the sources of the morality of human acts?The morality of human acts depends on three sources:
the object chosen, either a true or apparent good:
the intention of the subject who acts, that is, the purpose for which the subject performs the act; and
the circumstances of the act, which include its consequences.
Further reading: CCC 1749-1754, 1757-1758368. When is an act morally good?An act is morally good when it assumes simultaneously the goodness of the object, of the end, and of circumstances. A chosen object can by itself vitiate an act in its entirety, even if the intention is good. It is not licit to do evil so that good may result from it. An evil end corrupts the action, even if the object is good in itself. On the other hand, a good end does not make an act good if the object of that act is evil, since the end does not justify the means. Circumstances can increase or diminish the responsibility of the one who is acting but they cannot change the moral quality of the acts themselves. They never make good an act which is in itself evil.
Further reading: CCC 1755-1756, 1759-1760369. Are there acts which are always illicit?There are some acts which, in and of themselves, are always illicit by reason of their object (for example, blasphemy, homicide, adultery). Choosing such acts entails a disorder of the will, that is, a moral evil which can never be justified by appealing to the good effects which could possibly result from them.
Further reading: CCC 1756, 1761