The object, the intention, and the circumstances make up the three "sources" of the morality of human acts.
The object chosen morally specifies the act of willing accordingly as reason recognizes and judges it good or evil.
"An evil action cannot be justified by reference to a good intention" (cf St. Thomas Aquinas, Dec. praec. 6). the end does not justify the means.
A morally good act requires the goodness of its object, of its end, and of its circumstances together.
There are concrete acts that it is always wrong to choose, because their choice entails a disorder of the will, i.e., a moral evil. One may not do evil so that good may result from it.