285. Substance and Accidents (40). -- The substantial reality of a being that is in its own constitution and of itself capable of "subsisting" (potency), receives adventitious ontological determinations (acts) which are called accidents (ac-cidere). Scholasticism took up and developed very considerably the study of the nine categories of accidents, especially those of quality, quantity, relation, time and space.

The study of quality ("accidens modificativum substantiae in seipsa") raised some important questions not dealt with by Aristotle -- particularly that of the distinction between a substance and its operative powers. Can action result immediately from the substance of a contingent being; or can the latter act only by means of faculties? A much debated question in the thirteenth century, and one whose solution involved important metaphysical and psychological considerations. St. Thomas advocated the doctrine of a real distinction between the faculties and the substance of which they are qualities; he pointed to the accidental character of all activity in contingent things, and to the necessary identity of nature between this activity and its proximate principle. This view is in exact conformity with his metaphysical system. We have seen other scholastics establish closer connections between the substance and its faculties.