Moreover, saying that each contingent thing derives its existence from another that precedes it can mean either that it derives its existence from another thing that exists before it and continues to exist until the contingent effect comes into existence, or that it derives its existence from another thing that exists before it but also ceases to exist before it.

If the former is meant, then clearly, ruling out its deriving its existence from a contingent thing that exists concurrently with it covers both something that also existed before it and something that comes into existence only when it does. There is therefore no need to single out what existed before it, just as there is no need to single out what remains after it comes into existence. The proof encompasses everything that exists when it comes into existence, whether it also existed beforehand, also exists afterward, or was not in existence at the time of its existence.

If, however, what is meant is that it derives its existence from another thing that exists before it and also ceases to exist before it—which is what al-Rāzī intended—there is likewise no need to consider this case, for several reasons:

First:

If its deriving its existence from a contingent thing that exists concurrently with it is ruled out, then there is even stronger reason to rule out its deriving its existence from a contingent thing that no longer exists when it comes into existence. Thus, if the proof establishes the impossibility of an infinite regress of contingent causes while they coexist, the impossibility of such a regress when they occur successively is clearer and more evident.

Second:

The proof establishing the impossibility of an infinite regress of causes is unrestricted and general, whether those causes are assumed to coexist or to occur successively. For all that has been mentioned of