Anthropology as an Aid to Moral Science
Appendix 10. (785).
Generally speaking, St. Thomas teaches that `every SUBSISTENT thing is only one in number'. We can see this by comparing the following places of the Summa: I, q. 11, arts. 3 and 4, corp; q. 44, art. 1, corp; q. 75, art. 7, corp. For us what is subsistent and what is real are the same. In St. Thomas, we must distinguish the places where he is restricted to using accepted aristotelian language from the places where he speaks and thinks for himself. In the latter he manifests his genius and his own sureness of touch. It is not surprising, therefore, that opposing views are sometimes to be found in St. Thomas, the philosopher of the Schools and the original thinker. For example, in one place St. Thomas makes the following statement about the individuation under discussion: `Substance . . . is individuated of itself, but accidents are individuated by the subject, which is substance' (S.T., I, q. 29, art. 1, corp). This is the original thinker speaking, and if we understand substance as subsistence, reality, the statement exactly expresses our opinion. But we cannot deny that it seems very difficult to reconcile this statement of St. Thomas with the aristotelian statement, often found in his works, that `matter is the principle of individuation'. Matter is said to be the principle of individuation only because matter is considered as the source of the accidents, which terminate and complete the subject. Hence the statement that `an individual composed of matter and form subsists, relative to an accident, in dependence on matter'.
St. Thomas teaches this (S.T., I, q. 29, art. 2, ad 5) on the authority of a famous commentator of Aristotle (Boethius, De Trin., 2). But if matter is both that which permits the subject to subsist relative to the accidents, and the principle of individuation, the accidents would individuate the subject, which is contrary to the earlier statement that `accidents are individuated by the subject'. This is at least an apparent contradiction. However, the two statements can be reconciled by limiting both of them. The act of reality or subsistence in all real, subsistent beings is that which individuates them. But material, corporeal feeling does not subsist without matter. Thus, it is matter that makes this feeling subsist, drawing it to its determining substance, as we have explained. Matter, therefore, can be called the principle of individuation in that feeling.