the beam of radiance that inheres in the air, on walls, and the like, then this is not a substance—neither subtle nor dense—but an accident that depends on something else.

Fifth Aspect:

Your claim that “a subtle substance cannot admit an accident” is unacceptable and, in fact, false. The human soul plainly receives the accidents that inhere in it, and, for those who affirm its existence, the celestial soul likewise acquires ever-renewed volitions and perceptions. In the technical language of the dialecticians, the term “accident” denotes anything that subsists in another, whether it be a permanent attribute or a transient one. This is the division upheld by the Christians, just as it is by the philosophers.

They state that in existence there is nothing except substance or accident, for whenever we examine any entity we find it either self-subsistent, needing no other for its being—this they call substance—or dependent for its existence on something else, lacking any independent subsistence—and this they call accident. They further contend that no third category is possible.

This is precisely the classification propounded by Aristotle and his followers; he even refers to the First Cause as a substance, and all speculative thinkers adopt the same division. Most of them, however, do not include the Lord of all worlds within the designation “substance,” though some do, and part of the disagreement is purely verbal.

If their premise is granted, then the light that appears upon earth and in the air is an accident, not a self-subsistent substance. Yet they have counted it as a substance—an evident contradiction. Moreover, the subtle substances themselves are bearers of accidents such as life and knowledge; indeed, according to their own position, even the Lord possesses life and knowledge as attributes inhering in Him.