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.*
2.93 : That Intelligences Subsisting apart are not more than One in the same Species
2.96 : That Intelligences Subsisting apart do not gather their Knowledge from Objects of Sense