1. Having established that God is neither a body, nor made of anything, nor an instance of some species, nor something in which existence is accidental, Thomas next inquires whether God falls into any kind or genus.
2. In support of the view that God belongs to a community of kinds with creatures, St. Thomas raises two objections. First, he observes that God is a self-subsistent being, which is the definition of substance, which is one of the categories of being, i.e. a genus of things.
3. Second, he cites Averroes to the effect that God is the “measure of all substances”, and observes that what is measured can only be measured by something of the same kind.
4. For the Sed Contra, Thomas notes that nothing is prior to God, either in the intellect or in reality. But genera are intellectually prior to what is contained in them, since the contents of a genus are specifications of the generic form according to a difference. Therefore God is not in a genus, because if he were, he would properly be thought of as the specification or actualization of a generic form.
5. In the corpus, he first distinguishes two ways in which a thing can be said to be contained in a genus. The first way is properly, as species fall under genera. The second is analogically, as principles or privations ultimately reducible to a genus.
6. Against the notion that God is a species, he proposes three arguments: first, because a species is related to its genus as act to potency, i.e. the species is the actualization of a generic form according to a specific difference. But God is not the actualization of any prior form.
7. Second, because the genus of a thing is based on its essence, and God’s essence is “being”, it would follow that he would be in the genus “being”. But “being” cannot be a genus, because every proper genus is divisible into species by something outside of it. But no qualities or forms exist outside of “being” that could divide it. Therefore, since the genus to which he would belong cannot be a genus, it follows that God is not in a genus.
8. Third, because among the members of a genus there is a real community of form, which is actualized differently in the different individuals. Thus in the members of any genus there must be a difference between essence and existence, since the essence is the basis of the community, and the existence the basis of the distinction. But in God there is no distinction between essence and existence, as was shown in the previous article. Thus God is not in a genus.
9. Thomas pauses at this point to observe that because he is not a species or member of a genus, God cannot be defined, since the principles of a thing’s definition are its genus and difference.
10. As for being a principle reducible to some genus, St. Thomas points out that no principle which is reducible to a genus (e.g. “unity” to the genus of “discrete quantity”) extends beyond its genus. It seems that by "principle reducible to a genus", Thomas means the sorts of constitutive parts of a genus that, while not subsistent individuals, are still capable of dividing the genus. Thus a point has no substance, but it is the principle which determines and divides a line, in a way analogous to, but different from the way species divide and determine proper genera.
11. God, however, is the cause of the genus of being, and therefore can't be contained in it in this way.
12. In response to the first objection Thomas clarifies that substance signifies not only a subsistent essence, I.e. one that exists in its own right, nor existence as such, but an essence which exists, but which is distinct from its own existence. Thus God is not in the genus of substance.
13. To the second objection, he replies that while God is not proportionate to any creature, as "measures" normally are, still he can be called the measure of all that exists because everything that is exists only insofar as it is like God.
Outline of Article
– God subsists in himself and is therefore in the genus of substance.
– God is the measure of all things, and therefore must be of one kind with them.
– Genera are logically prior to species, but nothing is prior to God.
– God cannot be in a genus properly speaking, as a species, for three reasons: first because the species is the actualization of a potency in the genus; second, because God would have to be in the genus “being”, which cannot be a genus; third, because there cannot be a community of form between members of a genus without there being a difference between the individual act of being and the common essence.
– God cannot be reducible to a genus, as a principle or privation (“the unit” to discrete quantity, or “the unextended” to a continuous line), because such things do not exceed the genera which they constitute and divide, whereas God is the cause of the genus of being, and therefore cannot be contained in it in this way.
– Properly speaking, a substance is an essence which possesses the act of existing, in itself, but not of itself.
– God is the measure of all things only insofar as to be is to be like God.