ject of
contraries. But good and evil are contraries. Therefore the same
action cannot be both good and evil.

_I answer that,_ Nothing hinders a thing from being one, in so far as
it is in one genus, and manifold, in so far as it is referred to
another genus. Thus a continuous surface is one, considered as in the
genus of quantity; and yet it is manifold, considered as to the genus
of color, if it be partly white, and partly black. And accordingly,
nothing hinders an action from being one, considered in the natural
order; whereas it is not one, considered in the moral order; and vice
versa, as we have stated above (A. 3, ad 1; Q. 18, A. 7, ad 1). For
continuous walking is one action, considered in the natural order:
but it may resolve itself into many actions, considered in the moral
order, if a change take place in the walker's will, for the will is
the principle of moral actions. If therefore we consider one action
in the moral order, it is impossible for it to be morally both good
and evil. Whereas if it be one as to natural and not moral unity, it
can be both good and evil.

Reply Obj. 1: This continual movement which proceeds from various
intentions, although it is one in the natural order, is not one in
the point of moral unity.

Reply Obj. 2: Action and passion belong to the moral order, in so far
as they are voluntary. And therefore in so far as they are voluntary
in respect of wills that differ, they are two distinct things, and
good can be in one of them while evil is in the other.

Reply Obj. 3: The action of the servant, in so far as it proceeds
from the will of the servant, is not the master's action: but only in
so far as it proceeds from the master's command. Wherefore the evil
will of the servant does not make the action evil in this respect.
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QUESTION 21

OF THE CONSEQUENCES OF HUMAN ACTIONS BY REASON OF THEIR GOODNESS
AND MALICE (In Four Articles)

We have now to consider the consequences of human actions by reason
of their goodness and malice: and under this head there are four
points of inquiry:

(1) Whether a human action is right or sinful by reason of its being
good or evil?

(2) Whether it thereby deserves praise or blame?

(3) Whether accordingly, it is meritorious or demeritorious?

(4) Whether it is accordingly meritorious or demeritorious before God?
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FIRST ARTICLE [I-II, Q. 21, Art. 1]

Whether a Human Action Is Right or S