Nicene and Post-Nicene Fathers: Series I/Volume IV/Manichaean Controversy/On the Morals of the Manichaeans/Chapter 2
Chapter 2.—What Evil is. That Evil is that Which is Against Nature. In Allowing This, the Manichæans Refute Themselves.
2. You Manichæans often, if not in every case, ask those whom you try to bring over to your heresy, Whence is evil? Suppose I had now met you for the first time, I would ask you, if you please, to follow my example in putting aside for a little the explanation you suppose yourselves to have got of these subjects, and to commence this great inquiry with me as if for the first time. You ask me, Whence is evil? I ask you in return, What is evil? Which is the more reasonable question? Are those right who ask whence a thing is, when they do not know what it is; or he who thinks it necessary to inquire first what it is, in order to avoid the gross absurdity of searching for the origin of a thing unknown? Your answer is quite correct, when you say that evil is that which is contrary to nature; for no one is so mentally blind as not to see that, in every kind, evil is that which is contrary to the nature of the kind. But the establishment of this doctrine is the overthrow of your heresy. For evil is no nature, if it is contrary to nature. Now, according to you, evil is a certain nature and substance. Moreover, whatever is contrary to nature must oppose nature and seek its destruction. For nature means nothing else than that which anything is conceived of as being in its own kind. Hence is the new word which we now use derived from the word for being,—essence namely, or, as we usually say, substance,—while before these words were in use, the word nature was used instead. Here, then, if you will consider the matter without stubbornness, we see that evil is that which falls away from essence and tends to non-existence.
3. Accordingly, when the Catholic Church declares that God is the author of all natures and substances, those who understand this understand at the same time that God is not the author of evil. For how can He who is the cause of the being of all things be at the same time the cause of their not being,—that is, of their falling off from essence and tending to non-existence? For this is what reason plainly declares to be the definition of evil. Now, how can that race of evil of yours, which you make the supreme evil, be against nature, that is, against substance, when it, according to you, is itself a nature and substance? For if it acts against itself, it destroys its own existence; and when that is completely done, it will come at last to be the supreme evil. But this cannot be done, because you will have it not only to be, but to be everlasting. That cannot then be the chief evil which is spoken of as a substance. 
4. But what am I to do? I know that many of you can understand nothing of all this. I know, too, that there are some who have a good understanding and can see these things, and yet are so stubborn in their choice of evil,—a choice that will ruin their understanding as well,—that they try rather to find what reply they can make in order to impose upon inactive and feeble minds, instead of giving their assent to the truth. Still I shall not regret having written either what one of you may come some day to consider impartially, and be led to abandon your error, or what men of understanding and in allegiance to God, and who are still untainted with your errors, may read and so be kept from being led astray by your addresses.
- [On Augustin’s view of negativity of evil and on the relation of this view to Neo-Platonism, see Introduction, chapter IX. Augustin’s view seems to exclude the permanence of evil in the world, and so everlasting punishment and everlasting rebellion against God.—A.H.N.]