is impossible, and its failure to occur once those conditions are complete is likewise impossible. For if, after the completion of every causal condition, the effect were still absent, its absence would have to be either impossible or merely possible. If it were impossible, that would mean the act remains impossible even though the agent has fulfilled all the requisite conditions—an outright contradiction.

Now, suppose it truly were impossible. If that impossibility endured, the act could never occur at all, which flatly contradicts reality. If, however, it later became possible, this would mean it shifted from impossibility to possibility even though no new causal condition had arisen to render the agent effective.

It is self-evident that the transition from impossibility to possibility can occur only when something new appears that makes the act feasible. If nothing new has come about, the two situations are identical; to declare one impossible and the other possible would be to favor one of two equivalent alternatives without any differentiating factor—a notion that the intellect immediately rejects.

If it is said that, once the agent and all the conditions of causation were complete, the act remained merely possible—neither necessary nor impossible—then its occurrence at that very moment would be as possible as its occurrence later on. To single out one of the two moments for existence without a factor that tips the balance would again be preference without a preferer; and if such a preferent factor is required, that factor becomes part of the causal conditions, so that without it the act would be impossible, not merely possible. Thus one of two conclusions is unavoidable: either the contingent entity comes to be when its complete cause is present, or it fails to come to be when its complete cause is absent.

For this reason Muslims say, “Whatever Allah wills comes to be, and whatever He does not will does not come to be; so whatever He wills…"