The Ways to Wisdom
Aquinas Day By Day


Aquinas’s topic:  species is understood as genus and difference

Scripture:  “Get wisdom, get understanding.  Do not forget or turn aside from the words I utter.” Proverbs 4: 5

Aquinas’s text:  Summa theologiae I.3.5

In the course of explaining why God’s nature is not contained within some genus, Br. Thomas here makes use of the way he understands a logical species is composed of the genus under which the species falls and the difference that distinguishes one species from other species of that genus.

The question he asks is this:   Is God contained in a genus?


There are two ways some thing can be in a genus.  In one way, absolutely and properly, as a species that is contained under the genus.  In the other way, as being reducible to the genus, as principles and privations are in a genus. This is how point and unity are reduced to the genus of quantity, as principles of it; and blindness and every privation is reduced to the genus of the positive trait it lacks. Now God is not in a genus in either way. That God cannot be a species of some genus may be shown in three ways.

The first is because a species is constituted from its genus and difference. Now that from which the difference constituting the species is taken is always related to that from which the genus is taken, as act is related to potency. For “animal” is taken as a concrete term from the sensitive nature, since that is called “animal” which has a sensitive nature. But “rational” is taken from intellectual nature, because “rational” is what has an intellectual nature.  Now intellectual is compared to sensitive as act to potentiality. And the same thing holds for other species. Therefore, since in God potency is not joined to act, it is impossible that God be in a genus as its species.

Respondeo dicendum quod aliquid est in genere dupliciter. Uno modo simpliciter et proprie; sicut species, quae sub genere continentur. Alio modo, per reductionem, sicut principia et privationes, sicut punctus et unitas reducuntur ad genus quantitatis, sicut principia; caecitas autem, et omnis privatio, reducitur ad genus sui habitus. Neutro autem modo Deus est in genere. Quod enim non possit esse species alicuius generis, tripliciter ostendi potest.

Primo quidem, quia species constituitur ex genere et differentia. Semper autem id a quo sumitur differentia constituens speciem, se habet ad illud unde sumitur genus, sicut actus ad potentiam. Animal enim sumitur a natura sensitiva per modum concretionis; hoc enim dicitur animal, quod naturam sensitivam habet, rationale vero sumitur a natura intellectiva, quia rationale est quod naturam intellectivam habet, intellectivum autem comparatur ad sensitivum, sicut actus ad potentiam. Et similiter manifestum est in aliis. Unde, cum in Deo non adiungatur potentia actui, impossibile est quod sit in genere tanquam species.

[Introductions and translations © R.E. Houser]

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