Chapter 18

Is the soul the subject of all its potencies?

930. Everybody agrees that the soul is the principle of every action and potency. But some say that the subject of the potencies which need a corporeal organ is not the soul but the whole composite.(68) This is true from one point of view: the soul, in order to have a special sensation, must have an organic body. Consequently, its own activity does not arouse any special sensations within it - the same is true about every act needing corporeal organs.

931. Nevertheless I have shown that acts, potencies and habits depend on the same law, that is, 'they are activities aroused in the soul by entities different from the soul, but ontologically united to it as form and term.' Hence, the composite cannot be a subject of potencies, acts or habits. That which in the composite is not soul, is thought of as term, not principle. The subject, which is always understood as principle,(69) is the soul alone precisely because the soul is the one principle of all its activities. Some activities however need one term, others another. Thus, the intellective potency needs ideal being as its term, the sensitive potencies the body with its changes, and the rational potencies both ideal being and the body.

Notes

(68) S.T. , 1, q. 77, art. 5.

(69) This teaching seems to harmonise better with another thesis of St. Thomas that 'the potencies of the soul flow from its essence,' which he proves by the following principle: 'An accident proper [to the soul] is caused by the subject in so far as the subject is in act and received in the subject in so far as the subject is in potency.' St. Thomas is saying that potencies are accidents proper to the soul. They are therefore produced by the soul as by their subject, and received in the soul as in their subject. Cajetan explains St. Thomas' thought by saying that the potencies in the composite 'are from the soul because a composite is in act only BY REASON OF THE SOUL' (S.T. , 1, q. 77, art. 6).