on a separate mover, then that which has necessary existence in itself would be a body moving with a motion subsisting in it, for which it depends on something else.

It could then be said that the mover of the celestial sphere is likewise a body moving with a motion within it, whether or not it depends on something else for that motion. If it has no need of anything else, that is all the more tenable.

If it is said that the celestial sphere has contingent existence, that it must therefore depend on the Necessary Existent, and that the Necessary Existent is thus a cause that necessarily produces it, then the Necessary Existent must be its complete cause from eternity—for if it were not so, it would not be so.

No part of the effect of a complete cause can be delayed beyond that cause. Thus, if it is a complete cause of the celestial sphere’s motion, that motion must exist from eternity, which is impossible. If it is not its complete cause, something new must arise through which it becomes a complete cause of whatever motion occurs.

If this newly arising thing comes from the Necessary Existent, their position is invalidated. If it comes from the contingent being, their position is all the more untenable, for whatever comes from the contingent being must have come to it from the Necessary Existent, since it has nothing of itself.

This could serve as an argument at the outset of this question: if the perpetual motion of the celestial sphere proceeds from a necessitating cause, then, if that cause is its complete cause from eternity, no part of its effect can be delayed beyond it. If, however, the cause was not complete from eternity, it became a necessitating cause after not having been one.

If this completeness comes from itself, it would be moving, contrary to what they claim. If it comes from something else, then that which has necessary existence in itself would depend on something else for the completeness of its action.