Summa contra Gentiles1.25 Chapter XXV. That God is not in any genus

Hence it follows of necessity that God is not in any genus.

For whatever is in a genus, has in itself something whereby its generic nature is specified: for nothing is in a genus without being in some one of its species. But in God this is impossible, as shown above. Therefore it is impossible that God be in any genus.

Moreover. If God be in a genus, He is either in the genus of accident, or in that of substance. He is not in the genus of accident: for an accident cannot be the first being and first cause. /Nor can He be in the genus of substance: for substance that is a genus is not being itself, otherwise every substance would be its own being, and thus would not be caused by something else, which is impossible, as is clear from what we have said above. Now God is being itself. Therefore He is not in any genus./ Again. Whatever is in a genus differs as to being from the other things contained in the same genus: otherwise a genus would not be predicated of several things. Now all things that are contained in one same genus, must agree in the whatness of the genus, because the genus is predicated of all in respect of what a thing is. Therefore the being of anything contained in a genus is beside the whatness of the genus. But this is impossible in God. Therefore God is not in a genus.

Further. A thing is placed in a genus by the nature of its whatness, for genus is predicated of what a thing is. But the whatness of God is His very being. Now a thing is not placed in a genus according to its being, because then being would be a genus signifying being itself. It remains therefore that God is not in a genus.

That being cannot be a genus is proved by the Philosopher as follows. If being were a genus, it would be necessary to find a difference in order to contract it to a species. Now no difference participates in the genus, so that, to wit, the genus be contained in the notion of the difference, for thus the genus would be placed twice in the definition of the species: but the difference must be something besides that which is contained in the notion of the genus. Now there can be nothing besides that which is understood by being, if being belong to the notion of those things of which it is predicated. And thus by no difference can being be contracted. It remains, therefore, that being is not a genus: wherefore it follows of necessity that God is not in a genus.

Wherefore it is likewise evident that God cannot be defined: since every definition is composed of genus and difference.

It is also clear that no demonstration is possible in regard to Him: because the principle of a demonstration is the definition of that about which the demonstration is made.

Someone, however, might think that, although the name of substance cannot properly be applied to God, because God does not subsist under (substat) accidents: yet the thing signified by that term is applicable to Him, and consequently He is in the genus substance. For substance is (g, 2er se being, and it is clear that this can be applied to God, from the fact that it has been proved that He is not an accident. But to this we reply, according to what has been said, that per se being is not in the definition of substance. For from the fact that it is described as abeing it cannot be a genus, since it has been already proved that being has not the conditions of a genus: and again from 1 Ch. xxii. 2 2 Metaph. iii. 8. 3 Ch. xxiii.

the fact that it is described as being per se, for this would seem to denote nothing else than a negation, since it is said to be a per se being, through not being in another, which is a pure negation. And this cannot satisfy the conditions of a genus, for then a genus would not express what a thing is, but what it is not. Therefore we must understand the definition of substance in this way, that a substance is a thing to which it is fitting not to be in a subject: the word thing being taken from its quiddity, just as being is from existence: so that the meaning of substance is that it has a quiddity to which it is fitting to exist not in another. Now this does not apply to God, for He has no quiddity besides His existence. Hence it follows that He is nowise in the genus of substance: and consequently that He is in no genus, since it has been proved that He is not in the genus of accident.