Even if it is said, “Existence is necessary for the aggregate,” this is because the aggregate of existing things depends on the existence of each of them, whereas the existence of any one of them does not depend on the existence of the aggregate.

As for impossible things, the impossibility of their aggregate does not depend on the impossibility of each of them. Rather, each is inherently impossible, so the aggregate is all the more inherently impossible—unless, of course, the impossibility is conditional upon its individual members, as with two mutually dependent things, neither of which can exist without the other, although their coexistence is not impossible.

Likewise, if each contingent thing is contingent in itself, such that it needs an agent and does not exist by itself, then the contingency of each is neither conditional upon the other nor dependent on it. Nor does the contingency of one affect that of another. The same holds for impossibility. Existing things, however, are different: the existence of one of two things may either depend on the other or be its cause.

This differs from supposing existing things that are necessarily existent in themselves, for in that case the existence of some would not depend on the existence of others. As for something that is contingent in itself or impossible in itself, its contingency or impossibility is not conditional upon anything else. Rather, merely conceiving its essential nature entails knowing whether it is impossible or contingent.

Thus, the more numerous the instances of this nature become, the knowledge of their impossibility or contingency becomes