necessary and necessarily existent—though necessary through another—then they must first establish that there is a necessary being requiring a cause. This is the being necessary through another, of which they said that it is necessary throughout the eternal past and future and necessarily existent, yet necessary through another rather than through itself. For this reason they called it contingent.

He said:

“Nor has it yet been shown that there is a necessary being requiring a cause, such that supposing this would entail the existence of a necessary being without a cause, namely, one necessary through itself. Even if this were established first, it would then remain necessary to show that the totality of necessary beings, consisting of cause and effect, is like the totality of contingent beings.”

He means: If it were first established that a being could be necessary and necessarily existent throughout the eternal past and future, while nevertheless being the effect of another, one could say: This points to another necessary being, which is necessarily existent and is its cause. We would then need to say that there cannot exist a succession of causes and effects, each of them necessary, necessarily existent and beginningless, with its nonexistence impossible throughout the eternal past and future. An infinite regress among them would thus be invalid, just as an infinite regress is invalid in the case of what is truly contingent, namely, what is originated.

For it is known through reason, and agreed upon by rational people, that there cannot exist an infinite succession of originated things, each bringing another into existence, with no beginningless being among them. Thus, if the possibility of a beginningless, eternal effect were established, it would then be necessary to examine the impossibility of an infinite regress. Yet it has already been explained that, on this supposition, no proof can be given that such an infinite regress is impossible. How, then, could they do so when the very premise on which they based their argument has not been established?