That alternative we have already ruled out.

2. The only remaining possibility is an endless regress in which every single member of the series is preceded by another, with no first term at all. Because every other option has been dismissed, this one alone is left to be considered. It is formulated as follows: the eternal, self-existent Agent is—by virtue of His very essence—also a perpetual source of effusion; yet every event He brings about is preceded by another event, so that the cessation of the earlier one is a necessary pre-condition for the later one to flow forth from Him. In this fashion the First Principle is deemed the origin of the ever-changing occurrences.

They maintain that this has analogues in both natural motion and volitional motion.

With respect to natural motion: a lump of clay hurled upward returns to the earth because of its heaviness. The single factor responsible for that downward movement throughout the whole trajectory is its weight. Nevertheless, that weight could effect the body’s transition only from the second position to the third because the preceding segment of motion had first conveyed it to the second. Thus the occurrence and completion of the first segment are conditions that render it possible for the weight to act upon the body and move it from the second position to the third—and so on for every successive segment of the motion.

As for volitional motion: when someone intends to visit a friend, that intention is what moves the body from the person’s present location to the friend’s. Yet the influence of that intention in producing the second step is preceded by the occurrence and completion of the first step. According to this view, then, every prior step is