The point here is that what has been said about the impossibility of an infinite regress of causes applies whether they are conceived as successive or concurrent. Since their combination would then be an effect of them, it must all the more be contingent and unable to exist by itself. Nor can a contingent thing exist through another contingent thing that has nothing to bring it into existence. For what does not bring itself into existence is even less able to bring something else into existence. If none of the individual members brings itself into existence, it is even less able to bring anything else into existence—whether the whole or any other individual member.

This is made clear by the fact that a contingent thing does not exist by itself, but only through something else. If we suppose that contingent things exist, whether they are causes or not, and whether they are finite or infinite in number, none of them exists by itself. If the whole exists only through them, and none of them exists by itself, then nothing among all that has been mentioned exists by itself, whether taken collectively or individually. Whatever exists without existing by itself exists only through something else.

Do you not see that if someone were to say:

“Temporally originated things do not exist by themselves,”

there would be no difference between a finite and an infinite series of temporally originated things? Every member of an infinite series of temporally originated things likewise does not exist by itself, but must have an originator.

And when the mind conceives of a finite number of contingent things and a finite number of temporally originated things that have no