they asserted the existence of the genus of good and evil.
For Aristotle, especially in his logical works, brings forward
examples that in his time were probable in the opinion of some
philosophers. Or, it may be said that, as the Philosopher says
(Metaph. iv, text 6), "the first kind of contrariety is habit and
privation," as being verified in all contraries; since one contrary
is always imperfect in relation to another, as black in relation to
white, and bitter in relation to sweet. And in this way good and evil
are said to be genera not simply, but in regard to contraries;
because, as every form has the nature of good, so every privation, as
such, has the nature of evil.

Reply Obj. 2: Good and evil are not constitutive differences except
in morals, which receive their species from the end, which is the
object of the will, the source of all morality. And because good has
the nature of an end, therefore good and evil are specific
differences in moral things; good in itself, but evil as the absence
of the due end. Yet neither does the absence of the due end by itself
constitute a moral species, except as it is joined to the undue end;
just as we do not find the privation of the substantial form in
natural things, unless it is joined to another form. Thus, therefore,
the evil which is a constitutive difference in morals is a certain
good joined to the privation of another good; as the end proposed by
the intemperate man is not the privation of the good of reason, but
the delight of sense without the order of reason. Hence evil is not a
constitutive difference as such, but by reason of the good that is
annexed.

Reply Obj. 3: This appears from the above. For the Philosopher speaks
there of good and evil in morality. Because in that respect, between
good and evil there is a medium, as good is considered as something
rightly ordered, and evil as a thing not only out of right order, but
also as injurious to another. Hence the Philosopher says (Ethic. iv,
i) that a "prodigal man is foolish, but not evil." And from this evil
in morality, there may be a return to good, but not from any sort of
evil, for from blindness there is no return to sight, although
blindness is an evil.

Reply Obj. 4: A thing is said to act in a threefold sense. In one
way, formally, as when we say that whiteness makes white; and in that
sense evil considered even as a privation is said to corrupt good,
forasmuch as it is itself a corruption or pri