Reply Obj. 3: Evil is not in the good opposed to it as in its subject, but in some other good, for the subject of blindness is not "sight," but "animal." Yet, it appears, as Augustine says (Enchiridion 13), that the rule of dialectics here fails, where it is laid down that contraries cannot exist together. But this is to be taken as referring to good and evil in general, but not in reference to any particular good and evil. For white and black, sweet and bitter, and the like contraries, are only considered as contraries in a special sense, because they exist in some determinate genus; whereas good enters into every genus. Hence one good can coexist with the privation of another good.
Reply Obj. 4: The prophet invokes woe to those who say that good as such is evil. But this does not follow from what is said above, as is clear from the explanation given. _______________________
FOURTH ARTICLE [I, Q. 48, Art. 4]
Whether Evil Corrupts the Whole Good?
Objection 1: It would seem that evil corrupts the whole good. For one contrary is wholly corrupted by another. But good and evil are contraries. Therefore evil corrupts the whole good.
Obj. 2: Further, Augustine says (Enchiridion 12) that "evil hurts inasmuch as it takes away good." But good is all of a piece and uniform. Therefore it is wholly taken away by evil.
Obj. 3: Further, evil, as long as it lasts, hurts, and takes away good. But that from which something is always being removed, is at some time consumed, unless it is infinite, which cannot be said of any created good. Therefore evil wholly consumes good.
On the contrary, Augustine says (Enchiridion 12) that "evil cannot wholly consume good."
I answer that, Evil cannot wholly consume good. To prove this we must consider that good is threefold. One kind of good is wholly destroyed by evil, and this is the good opposed to evil, as light is wholly destroyed by darkness, and sight by blindness. Another kind of good is neither wholly destroyed nor diminished by evil, and that is the good which is the subject of evil; for by darkness the substance of the air is not injured. And there is also a kind of good which is diminished by evil, but is not wholly taken away; and this good is the aptitude of a subject to some actuality.
The diminution, however, of this kind of good is not to be considered by way of subtraction, as diminution in quantity, but rather by way of remission, as diminution in qualities and forms. The remission likewise of this habitude is to be taken as contrary to its intensity. For this kind of aptitude receives its intensity by the dispositions whereby the matter is prepared for actuality; which the more they are multiplied in the subject the more is it fitted to receive its perfection and form; and, on the contrary, it receives its remission by contrary dispositions which, the more they are multiplied in the matter, and the more they are intensified, the more is the potentiality remitted as regards the actuality.