Article II. On the Sources of Morality

The sources of morality are named those principles which bestow upon human acts their species, or a modification of the species, in the genus of morals.

Three sources of morality are numbered, namely: 1st, the object of the act; 2nd, its circumstances; 3rd, the end of the agent. These three are altogether required for a good act; if even one is bad, the act will become bad. Hence the well-known axiom: Good is from an integral cause, evil from any defect whatsoever.