The absence of a requisite cause is more appropriately linked to the absence of its effect than the converse. The reason is that, because the existence of the requisite is what actually yields the existence of the thing it necessitates, the intellect naturally assigns the non-occurrence of the effect to the non-existence of its requisite as a necessary correlation. For the non-existence of anything can only result from one of two matters: either the requisite cause is lacking, or a preventing factor is present. Once the requisite has been established, the effect can fail to appear only for one of these two reasons. Hence, when the causal factor that should bring a thing into being has indeed come together, but an existing impediment hinders and thwarts it, at times the non-existence of the thing is attributed to the absence of its requisite, and at other times to the presence of its impediment and antagonist.

This is the meaning of the Muslims’ dictum: “Whatever Allah wills comes to be, and whatever He does not will never comes to be.” His will alone is the only efficient cause; therefore, the negation of His will necessarily entails the non-existence of the thing. Nothing exists until He wills it, and nothing can ever exist without His will. We possess no cause that could bring a thing into existence while His will prevents it. Rather, His will is the complete and sufficient cause: when it is present, nothing can obstruct it, and when it is absent, no requisite cause remains. “Whatever mercy Allah opens up for people, none can withhold it…” (Fatir 2).