Now it is clear, from what has been said (A. 5), that either the subject of the soul's powers is the soul itself alone, which can be the subject of an accident, forasmuch as it has something of potentiality, as we have said above (A. 1, ad 6); or else this subject is the composite. Now the composite is actual by the soul. Whence it is clear that all the powers of the soul, whether their subject be the soul alone, or the composite, flow from the essence of the soul, as from their principle; because it has already been said that the accident is caused by the subject according as it is actual, and is received into it according as it is in potentiality.
Reply Obj. 1: From one simple thing many things may proceed naturally, in a certain order; or again if there be diversity of recipients. Thus, from the one essence of the soul many and various powers proceed; both because order exists among these powers; and also by reason of the diversity of the corporeal organs.
Reply Obj. 2: The subject is both the final cause, and in a way the active cause, of its proper accident. It is also as it were the material cause, inasmuch as it is receptive of the accident. From this we may gather that the essence of the soul is the cause of all its powers, as their end, and as their active principle; and of some as receptive thereof.
Reply Obj. 3: The emanation of proper accidents from their subject is not by way of transmutation, but by a certain natural resultance; thus one thing results naturally from another, as color from light. _______________________
SEVENTH ARTICLE [I, Q. 77, Art. 7]
Whether One Power of the Soul Arises from Another?
Objection 1: It would seem that one power of the soul does not arise from another. For if several things arise together, one of them does not arise from another. But all the powers of the soul are created at the same time with the soul. Therefore one of them does not arise from another.
Obj. 2: Further, the power of the soul arises from the soul as an accident from the subject. But one power of the soul cannot be the subject of another; because nothing is the accident of an accident. Therefore one power does not arise from another.
Obj. 3: Further, one opposite does not arise from the other opposite; but everything arises from that which is like it in species. Now the powers of the soul are oppositely divided, as various species. Therefore one of them does not proceed from another.
On the contrary, Powers are known by their actions. But the action of one power is caused by the action of another power, as the action of the imagination by the action of the senses. Therefore one power of the soul is caused by another.