When it is said, “A fully sufficient cause necessarily entails its effect, so if the effect were to arise later this would amount to preference without a preferrer,” we reply that what is not a fully sufficient cause is likewise unable, of itself, later to become fully sufficient, for that too would involve preference without a preferrer.

There is, moreover, a second argument showing the impossibility of this alternative. Suppose the cause is not fully sufficient, yet it brings about something whereby it becomes fully sufficient. The very act of bringing that about would require it to be fully sufficient with respect to what it produced, while the supposition is that it is not fully sufficient with respect to anything whatsoever. It would therefore have to be a cause in some respect in order not to be a cause in any respect—a direct conjunction of two contradictories.

This belongs to the category of vicious circularity a priori (dawr qabli): it cannot be a cause until it is already a cause, and it is not a cause until it has become a cause. It is like saying, “It does not exist until after it exists, and it does not come to exist until after it exists.” Such circularity is intrinsically impossible.

It is also a variety of infinite regress at the very root of causation, though the later thinkers called it “regress.” They said: if the totality of what the world’s existence depends upon were in place from pre-eternity, the world itself would necessarily exist, for an effect cannot fail to follow a present cause. If, however, it were not in place from pre-eternity and something then occurred whereby it became the cause of the world, the same argument applies to that occurrence—and a regress ensues. In other words, that occurrence will not take place until something prior to it takes place by which the agent becomes an agent, and that occurrence itself will not take place until something prior to it takes place by which