reason," and evil is "to be against
reason." For that is good for a thing which suits it in regard to its
form; and evil, that which is against the order of its form. It is
therefore evident that the difference of good and evil considered in
reference to the object is an essential difference in relation to
reason; that is to say, according as the object is suitable or
unsuitable to reason. Now certain actions are called human or moral,
inasmuch as they proceed from the reason. Consequently it is evident
that good and evil diversify the species in human actions; since
essential differences cause a difference of species.

Reply Obj. 1: Even in natural things, good and evil, inasmuch as
something is according to nature, and something against nature,
diversify the natural species; for a dead body and a living body are
not of the same species. In like manner, good, inasmuch as it is in
accord with reason, and evil, inasmuch as it is against
reason, inasmuch as it is against reason, diversify the moral species.

Reply Obj. 2: Evil implies privation, not absolute, but affecting
some potentiality. For an action is said to be evil in its species,
not because it has no object at all; but because it has an object in
disaccord with reason, for instance, to appropriate another's
property. Wherefore in so far as the object is something positive, it
can constitute the species of an evil act.

Reply Obj. 3: The conjugal act and adultery, as compared to reason,
differ specifically and have effects specifically different; because
the other deserves praise and reward, the other, blame and
punishment. But as compared to the generative power, they do not
differ in species; and thus they have one specific effect.

Reply Obj. 4: A circumstance is sometimes taken as the essential
difference of the object, as compared to reason; and then it can
specify a moral act. And it must needs be so whenever a circumstance
transforms an action from good to evil; for a circumstance would not
make an action evil, except through being repugnant to reason.
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SIXTH ARTICLE [I-II, Q. 18, Art. 6]

Whether an Action Has the Species of Good or Evil from Its End?

Objection 1: It would seem that the good and evil which are from the
end do not diversify the species of actions. For actions derive their
species from the object. But the end is altogether apart from the
object. Therefore the good and evil which are from the end do not
d