As for the third, it does not establish the eternity of the heavens, since there may be an act subsisting in His essence followed by another act, or one effect followed by another, or both.
Al-Āmidī, al-Abharī, and others have presented this argument and answered it by countering it with the temporal events that occur daily.
[Al-Āmidī’s discussion in “Daqā’iq al-haqā’iq” (The Subtleties of Realities)]
Al-Āmidī’s discussion in Daqā’iq al-haqā’iq
Presenting the argument for their position in Daqā’iq al-haqā’iq, al-Āmidī said:
If what proceeds from the intrinsically Necessary Existent were temporally originated, existing after nonexistence, then in itself it would be either necessary, impossible, or possible.
It cannot be necessary, for otherwise it would never have been nonexistent. Nor can it be impossible, for otherwise it would never have existed. Thus, it can only be intrinsically possible.
If, then, it came into being without an originator and determining factor, one of the two alternatives for a possible being would have prevailed without a determining factor, which is impossible. If it came into being through an originator and determining factor, that determining factor must be either eternal or temporally originated.
If it is temporally originated, the same reasoning applies to it as to the first, while infinite regress and circularity are impossible. Thus, the determining factor must either be eternal or ultimately depend upon an eternal determining factor.
Either everything indispensable for bringing the effect into existence was eternally present together with that eternal determining factor, or something remained to be awaited.
If something remained to be awaited, the same reasoning applies to its coming into being as to the first, necessarily resulting in infinite regress or circularity, which is impossible. If the first alternative holds, the eternity of the cause entails the eternity of the effect.
The same ruling applies to what necessarily proceeds from the Necessary through that which is intrinsically necessary.
Al-Āmidī said in reply:
This entails the existence of some temporal event. For