§7. Refutation of dualism from reason. Impossibility of two Gods. The truth as to evil is that which the Church teaches: that it originates, and resides, in the perverted choice of the darkened soul.
More especially, they are exposed to the following reply. If visible things are the work of the evil god, what is the work of the good God? for nothing is to be seen except the work of the Artificer. Or what evidence is there that the good God exists at all, if there are no works of His by which He may be known? for by his works the artificer is known. 2. Or how could two principles exist, contrary one to another: or what is it that divides them, for them to exist apart? For it is impossible for them to exist together, because they are mutually destructive. But neither can the one be included in the other, their nature being unmixed and unlike. Accordingly that which divides them will evidently be of a third nature, and itself God. But of what nature could this third something be? good or evil? It will be impossible to determine, for it cannot be of the nature of both. 3. This conceit of theirs, then, being evidently rotten, the truth of the Churchs theology must be manifest: that evil has not from the beginning been with God or in God, nor has any substantive existence; but that men, in default of the vision of good, began to devise and imagine for themselves what was not, after their own pleasure. 4. For as if a man, when the sun is shining, and the whole earth illumined by his light, were to shut fast his eyes and imagine darkness where no darkness exists, and then walk wandering as if in darkness, often falling and going down steep places, thinking it was dark and not light,—for, imagining that he sees, he does not see at all;—so, too, the soul of man, shutting fast her eyes, by which she is able to see God, has imagined evil for herself, and moving therein, knows not that, thinking she is doing something, she is doing nothing. For she is imagining what is not, nor is she abiding in her original nature; but what she is is evidently the product of her own disorder. 5. For she is made to see God, and to be enlightened by Him; but of her own accord in Gods stead she has sought corruptible things and darkness, as the Spirit says somewhere in writing, “God made man upright, but they have sought out many inventions 115 .” Thus it has been then that men from the first discovered and contrived and imagined evil for themselves. But it is now time to say how they came down to the madness of idolatry, that you may know that the invention of idols is wholly due, not to good but to evil. But what has its origin in evil can never be pronounced good in any point,—being evil altogether.
Eccl. vii. 29.