and, 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.
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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 ev