(CG 2/93). That Intelligences subsisting apart are not more than one in the... (Book 2: God The Origin of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

A DIFFERENT type of being makes a different species. But the being of the human soul and of an intelligence subsisting apart is not of one type: the body can have no share in the being of a separately subsisting intelligence, as it can have in the being of the human soul, united with the body as form with matter.

3. What makes a species by itself cannot be of the same species with that which does not make a species by itself, but is part of a species. Now a separately subsisting intelligence makes a species by itself, but a soul not, it is part of the human species.

4. The species of a thing may be gathered from the activity proper to it: for activity shows power, and that is an indication of essence. Now the proper activity of a separately subsisting intelligence and of an intelligent soul is understanding. But the mode of understanding of a separately subsisting intelligence is quite different from that of the soul. The soul understands by taking from phantasms: not so the separately subsisting intelligence, that has no bodily organs in which phantasms should be.