through something else? And how—how can it owe its existence to something equally lacking any claim to existence?

This is made clear by the following: if this thing has no claim to existence, and that thing has no claim to existence, then making the former the cause and the latter its effect is no more justified than the reverse. For an agent must exist; if it does not exist, it cannot act. Neither of them has any claim to exist, so neither can be an agent.

If someone says, “One of these two came into existence through the other,” this is intelligible only if the other exists. Yet that other does not exist through itself; it exists only through something else. The other upon which a contingent thing depends cannot be just anything whatsoever. Rather, it must be something that brings about its existence in such a way that nothing beyond it is needed. Thus, the other upon which a contingent thing depends must independently bring that contingent thing into existence, without itself needing anything else in any respect whatsoever.

Whenever it is supposed that this other needs something else, the contingent thing then needs both this other and the further thing upon which it depends. Its existence is therefore not brought about through either one of the two alone; both are indispensable. Likewise, however many other things may be supposed, that upon which the contingent thing depends must have no need of anything else in any respect whatsoever. No contingent thing meets this condition; rather, each needs something else. So if it were supposed that a contingent thing exists through another contingent thing, in a finite or infinite series, and that the aggregate