It is known that whatever comes into existence cannot be eternal, for the two are contradictory: to say that something comes into existence means that it is not eternal.

It is also known that whatever is necessary in itself must be eternal. That whatever is necessary in itself must be eternal is more evidently known than that whatever is eternal must be necessary in itself. No known group has disputed the former, whereas a known group has disputed the latter.

Moreover, Abū al-Husayn argued that whatever is eternal must be necessary in itself on the grounds that its existence at one time has no priority over its existence at another. Thus, its existence must be necessary at every time, making its nonexistence impossible.

That whatever is necessary in itself must be eternal, however, is more evident than this.

Accordingly, it cannot be said of what comes into existence that it came into existence while being … [The impossibility of] its coming into existence while being necessary in itself is more evident than the fact that its existence at one time has no priority over its existence at another.

Abū al-Husayn based his argument on denying this priority, which amounts to saying that the two times are equal. Neither time, therefore, can be singled out over the other for something to come into existence without something that singles it out.

This alone suffices as the starting point of his argument: whatever comes into existence does so at a particular time, and singling out one of the two times necessarily requires something that singles it out.