Nicene and Post-Nicene Fathers, Vol. II:
City of God: Chapter 10

Chapter 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 p. 211 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.

It is for this reason, then, that the nature of the Trinity is called simple, because it has not anything which it can lose, and because it is not one thing and its contents another, as a cup and the liquor, or a body and its color, or the air and the light or heat of it, or a mind and its wisdom.  For none of these is what it has:  the cup is not liquor, nor the body color, nor the air light and heat, nor the mind wisdom.  And hence they can be deprived of what they have, and can be turned or changed into other qualities and states, so that the cup may be emptied of the liquid of which it is full, the body be discolored, the air darken, the mind grow silly.  The incorruptible body which is promised to the saints in the resurrection cannot, indeed, lose its quality of incorruption, but the bodily substance and the quality of incorruption are not the same thing.  For the quality of incorruption resides entire in each several part, not greater in one and less in another; for no part is more incorruptible than another.  The body, indeed, is itself greater in whole than in part; and one part of it is larger, another smaller, yet is not the larger more incorruptible than the smaller.  The body, then, which is not in each of its parts a whole body, is one thing; incorruptibility, which is throughout complete, is another thing;—for every part of the incorruptible body, however unequal to the rest otherwise, is equally incorrupt.  For the hand, e.g., is not more incorrupt than the finger because it is larger than the finger; so, though finger and hand are unequal, their incorruptibility is equal.  Thus, although incorruptibility is inseparable from an incorruptible body, yet the substance of the body is one thing, the quality of incorruption another.  And therefore the body is not what it has.  The soul itself, too, though it be always wise (as it will be eternally when it is redeemed), will be so by participating in the unchangeable wisdom, which it is not; for though the air be never robbed of the light that is shed abroad in it, it is not on that account the same thing as the light.  I do not mean that the soul is air, as has been supposed by some who could not conceive a spiritual nature; 468 but, with much dissimilarity, the two things have a kind of likeness, which makes it suitable to say that the immaterial soul is illumined with the immaterial light of the simple wisdom of God, as the material air is irradiated with material light, and that, as the air, when deprived of this light, grows dark, (for material darkness is nothing else than air wanting light, 469 ) so the soul, deprived of the light of wisdom, grows dark.

According to this, then, those things which are essentially and truly divine are called simple, because in them quality and substance are identical, and because they are divine, or wise, or blessed in themselves, and without extraneous supplement.  In Holy Scripture, it is true, the Spirit of wisdom is called “manifold” 470 because it contains many things in it; but what it contains it also is, and it being one is all these things.  For neither are there many wisdoms, but one, in which are untold and infinite treasures of things intellectual, wherein are all invisible and unchangeable reasons of things visible and changeable which were created by it. 471   For God made nothing unwittingly; not even a human workman can be said to do so.  But if He knew all that He made, He made only those things which He had known.  Whence flows a very striking but true conclusion, that this world could not be known to us unless it existed, but could not have existed unless it had been known to God.

Footnotes

Plutarch (De Plac. Phil. i. 3, and iv. 3) tells us that this opinion was held by Anaximenes of Miletus, the followers of Anaxagoras, and many of the Stoics.  Diogenes the Cynic, as well, as Diogenes of Appollonia seems to have adopted the same opinion.  See Zeller’s Stoics, pp. 121 and 199.

Ubi lux non est, tenebræ sunt, non quia aliquid sunt tenebræ, sed ipsa lucis absentia tenebræ dicuntur.—Aug. De. Gen. contra Man. 7.

Wisd. 7.22.

The strongly Platonic tinge of this language is perhaps best preserved in a bare literal translation.