On the contrary, the Philosopher says (Ethic. ii, 3) that a virtuous man acts as he should, and when he should, and so on in respect of the other circumstances.  Therefore, on the other hand, the vicious man, in the matter of each vice, acts when he should not, or where he should not, and so on with the other circumstances.  Therefore human actions are good or evil according to circumstances.

I answer that, In natural things, it is to be noted that the whole fulness of perfection due to a thing, is not from the mere substantial form, that gives it its species; since a thing derives much from supervening accidents, as man does from shape, color, and the like; and if any one of these accidents be out of due proportion, evil is the result.  So it is with action.  For the plenitude of its goodness does not consist wholly in its species, but also in certain additions which accrue to it by reason of certain accidents:  and such are its due circumstances.  Wherefore if something be wanting that is requisite as a due circumstance the action will be evil.

Reply Obj. 1:  Circumstances are outside an action, inasmuch as they are not part of its essence; but they are in an action as accidents thereof.  Thus, too, accidents in natural substances are outside the essence.

Reply Obj. 2:  Every accident is not accidentally in its subject; for some are proper accidents; and of these every art takes notice.  And thus it is that the circumstances of actions are considered in the doctrine of morals.

Reply Obj. 3:  Since good and being are convertible; according as being is predicated of substance and of accident, so is good predicated of a thing both in respect of its essential being, and in respect of its accidental being; and this, both in natural things and in moral actions. ________________________

FOURTH ARTICLE [I-II, Q. 18, Art. 4]

Whether a Human Action Is Good or Evil from Its End?

Objection 1:  It would seem that the good and evil in human actions are not from the end.  For Dionysius says (Div.  Nom. iv) that “nothing acts with a view to evil.”  If therefore an action were good or evil from its end, no action would be evil.  Which is clearly false.

Obj. 2:  Further, the goodness of an action is something in the action.  But the end is an extrinsic cause.  Therefore an action is not said to be good or bad according to its end.

Obj. 3:  Further, a good action may happen to be ordained to an evil end, as when a man gives an alms from vainglory; and conversely, an evil action may happen to be ordained to a good end, as a theft committed in order to give something to the poor.  Therefore an action is not good or evil from its end.

On the contrary, Boethius says (De Differ. Topic. ii) that “if the end is good, the thing is good, and if the end be evil, the thing also is evil.”