This line of reasoning, then, proves only the presence of a final cause; it in no way demonstrates an efficient cause. Grant, for argument’s sake, that the motion in question is volitional, and that every volitional motion must have some beloved goal it seeks. What, then, is the productive, efficient source that brings about this yearning, volitional motion?

If one were to claim that the celestial sphere is necessary in and of itself, that would not in fact reflect their doctrine—and the claim would be unsound on two counts.

First, a being that is necessary through itself can never stand in need of anything else, whether an efficient cause or a final cause. Thus, if you attribute to it a final cause on which it depends for its will and movement, it is no longer self-sufficient and therefore cannot be necessary in itself.

Second, once it is conceded that the sphere could be necessary by its very nature, it is equally possible to say that it serves as the final cause of its own motion, just as it is said to be the efficient cause of that motion. A fuller treatment of the flaws in their position has been offered elsewhere.

As for Ibn Sīnā and his adherents, they turned away from this path and adopted a method that blends the approach of the theologians with that of the earlier philosophers. They declared: “Whatever exists is either necessary or contingent, and the contingent requires a necessary being,” much as the theologians say: “Whatever exists is either originated or eternal, and the originated must depend upon an eternal cause.”