(CG 1/025). That God is not in any Genus (Book 1: Of God As He Is In Himself) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

THINGS are not distinguished from one another in so far as they all have being, because in this they all agree. If therefore things do differ from one another, either 'being' itself must be specified by certain added differentias, so that different things have a different specific being; or things must differ in this that 'being' itself attaches to specifically different natures. The first alternative is impossible, because no addition can be made to 'being,' in the way that differentia is added to genus, as has been said (Chap. XXV, n. 4). It remains therefore that things differ in that they have different natures, to which 'being' accrues differently. But the divine being is not something accessory to any nature, but is the very nature or essence of God (Chap. XXII). If therefore the divine being were the formal and abstract being of all things, all things would have to be absolutely one.

4. What is common to many is not anything over and above the many except in thought alone. For example, 'animal' is not anything over and above Socrates and Plato and other animals, except in the mind that apprehends the form of 'animal' despoiled of all individualising and specifying marks: for what is really animal is man: otherwise it would follow that in Plato there were several animals, to wit, animal in general, and man in general, and Plato himself. Much less then is bare being in general anything over and above all existing things, except in the mind alone. If then God be being in general, God will be nothing more than a logical entity, something that exists in the mind alone.

This error is set aside by the teaching of Holy Scripture, which confesses God lofty and high (Isa. vi, 1), and that He is above all (Rom. ix, 5). For if He is the being of all, then He is something of all, not above all. The supporters of this error are also cast out by the same sentence which casts out idolaters, who gave the incommunicable name of God to stocks and stones (Wisd. xiv, 8, 21). For if God were the being of all, it would not be more truly said, 'A stone is a being,' than 'A stone is God.'

What has led men into this error is a piece of faulty reasoning. For, seeing that what is common to many is specialised and individualised by addition, they reckoned that the divine being, to which no addition is made, was not any individual being, but was the general being of all things: failing to observe that what is common or universal cannot really exist without addition, but merely is viewed by the mind without addition. 'Animal' cannot be without 'rational' or 'irrational' as a differentia, although it may be thought of without these differentias. Moreover, though the universal be thought of without addition, yet not without susceptibility of addition. 'Animal' would not be a genus if no differentia could be added to it; and so of other generic names. But the divine being is without addition, not only in thought, but also in rerum natura; and not only without addition, but without even susceptibility of addition. Hence from this very fact, that He neither receives nor can receive addition, we may rather conclude that God is not being in general, but individual being: for by this very fact His being is distinguished from all other beings, that nothing can be added to it. (Chap. XXIV).