Chapter 87 — That the possible intellect and agent intellect are founded in the soul’s essence

Since the agent intellect and the possible intellect are formally united to us, we must acknowledge that they pertain to the same essence of the soul. Whatever is formally united to another thing is united to it either in the manner of a substantial form or in the manner of an accidental form. If the possible intellect and the agent intellect were united to man after the fashion of a substantial form, we would have to hold that they share in the one essence of that form which is the soul, since one thing cannot have more than one substantial form. On the other hand, if they are united to man after the fashion of an accidental form, neither of them, evidently, can be an accident of the body. Besides, the fact that their operations are performed without a bodily organ, as we proved above, shows that each of them is an accident of the soul. But there is only one soul in one man. Therefore, the agent intellect and the possible intellect must belong to the one essence of the soul.

Furthermore, every action that is proper to a species is from principles consequent upon the form which confers the species. But the action of understanding is an operation proper to the human species. Therefore, the agent intellect and the possible intellect, which are principles of this action, as has been shown, are consequent upon the human soul, whence man has his species. However, they do not issue from the soul in such a way as to extend to the body, because, as we have said, the operation in question takes place independently of a bodily organ. Since, therefore, action pertains to the same subject as does potency, the possible intellect and the agent intellect belong to the one essence of the soul.