[Ibn Taymiyya’s commentary]

I say:

The substance of this argument is that an act can be necessary in existence and must therefore exist perpetually, since otherwise its existence and nonexistence would both be possible.

What is meant here is that it can exist perpetually through another; hence, its perpetual existence must be necessary through another, not in itself. For if its existence were necessary neither in itself nor through another, but its nonexistence were possible, then its nonexistence would have to be possible at all times. It is impossible for its nonexistence to be possible at one time but not another when the circumstances are identical. Moreover, the possibility of its perpetual nonexistence is incompatible with its existence being necessary, whether in itself or through another, at any time. For if its existence were necessary at any time, whether in itself or through another, its nonexistence could not be possible while its existence was necessary. Whenever it exists, it exists through another and is therefore necessary through another. Thus, while it exists, its nonexistence cannot be possible. If, then, its nonexistence is assumed to be possible at all times, such that its existence is necessary neither in itself nor through another, it cannot exist under any circumstances.

Yet the supposition is that its existence is possible—indeed, that its perpetual existence is possible. The possibility of existence is incompatible with the impossibility of existence. Thus, whatever can exist perpetually cannot fail to exist.

The crux of the argument is that whatever can exist perpetually is, while it exists, necessary through another. For if a contingent thing is accompanied by that which necessitates its existence, it becomes necessary through another. If it is not accompanied by that which necessitates its existence, its existence becomes impossible owing to something else. A contingent thing comes into existence only in the presence of a fully sufficient determining factor that necessitates its existence. For if its existence were not necessary in the presence of that factor, it would remain contingent; and if it were contingent, its existence could not prevail over its nonexistence without a determining factor.

This point has been disputed by groups among the Mu‘tazilites and other speculative theologians. One group says that an agent endowed with power favors one of two equivalent alternatives within his power without