Of God and His Creatures

This is a bit of Platonism that has passed through Aristotle to St Thomas. St Thomas gives the example of fire being the cause of all things fiery. But there is no essential element of fire, any more than there is any essential beauty, outside of God. There is no actual essential nature anywhere in creation. Thus there is no actual essential humanity, by participation in which all men are men. Aristotle's doctrine of the four elements, fire being essentially hot, air essentially cold, earth essentially dry, and water essentially moist, is really a scheme of Platonic Ideas operating as physical causes. For all his protests against the Ideas, Aristotle never became quite emancipated from their control.

Of God and His Creatures: 3.66