The City of God, Volume I

the Lord, but darkness in themselves, being deprived of the participation of Light eternal. For evil has no positive nature; but the loss of good has received the name "evil."[462]

10. Of the simple and unchangeable Trinity, Father, Son, and Holy Ghost, one God, in whom substance and quality are identical.

There is, accordingly, a good which is alone simple, and therefore alone unchangeable, and this is God. By this Good have all others been created, but not simple, and therefore not unchangeable. "Created," I say,--that is, made, not begotten. For that which is begotten of the simple Good is simple as itself, and the same as itself. These two we call the Father and the Son; and both together with the Holy Spirit are one God; and to this Spirit the epithet Holy is in Scripture, as it were, appropriated. And He is another than the Father and the Son, for He is neither the Father nor the Son. I say "another," not "another thing," because He is equally with them the simple Good, unchangeable and co-eternal. And this Trinity is one God; and none the less simple because a Trinity. For we do not say that the nature of the good is simple, because the Father alone possesses it, or the Son alone, or the Holy Ghost alone; nor do we say, with the Sabellian heretics, that it is only nominally a Trinity, and has no real distinction of persons; but we say it is simple, because it is what it has, with the exception of the relation of the persons to one another. For, in regard to this relation, it is true that the Father has a Son, and yet is not Himself the Son; and the Son has a Father, and is not Himself the Father. But, as regards Himself, irrespective of relation to the other, each is what He has; thus, He is in Himself living, for He has life, and is Himself the Life which He has.