1 Faustus said: Do we believe in one God or in two? In one, of course. If we are accused of making two gods, I reply that it cannot be shown that we ever said anything of the kind. Why do you suspect us of this? Because, you say, you believe in two principles, good and evil. It is true, we believe in two principles; but one we call God, and the other Hyle, or, to use common popular language, the devil. If you think this means two gods, you may as well think that the health and sickness of which doctors speak are two kinds of health, or that good and evil are two kinds of good, or that wealth and poverty are two kinds of wealth.
If I were describing two things, one white and the other black, or one hot and the other cold, or one sweet and the other bitter, it would appear like idiocy or insanity in you to say that I was describing two white things, or two hot things, or two sweet things. So, when I assert that there are two principles, God and Hyle, you have no reason for saying that I believe in two gods. Do you think that we must call them both gods because we attribute, as is proper, all the power of evil to Hyle, and all the power of good to God?
If so, you may as well say that a poison and the antidote must both be called antidotes, because each has a power of its own, and certain effects follow from the action of both. So also, you may say that a physician and a poisoner are both physicians; or that a just and an unjust man are both just, because both do something. If this is absurd, it is still more absurd to say that God and Hyle must both be gods, because they both produce certain effects. It is a very childish and impotent way of arguing, when you cannot refute my statements, to make a quarrel about names.
I grant that we, too, sometimes call the hostile nature God; not that we believe it to be God, but that this name is already adopted by the worshippers of this nature, who in their error suppose it to be God. Thus the apostle says: "The god of this world has blinded the minds of them that believe not." He calls him God, because he would be so called by his worshippers; adding that he blinds their minds, to show that he is not the true God.
Source: Reply to Faustus the Manichaean (New Advent)