possible—as with knowledge together with life: knowledge by itself is impossible, but together with life it is possible. Likewise, either of two contraries is possible by itself, but their coexistence becomes impossible when one is joined to the other. Thus, of two inseparable correlates, neither can exist in isolation, whereas two contraries cannot coexist.

This makes clear the difference between the perpetual and uninterrupted succession of effects that come into being and pass away, and the existence of an endless series of possible causes and effects. Some people deemed both categories impossible, as do many dialectical theologians. Others imagined that aggregation had the same effect with respect to possibility and impossibility; consequently, the impossibility of an endless series of causes and effects was not clear to them. They regarded this as a difficult point (1) for whose impossibility no proof could be established, even though no one actually held such a position. This was stated by al-Āmidī in Rumūz al-Kunūz (Symbols of the Treasures) (2), and by al-Abharī (3) [and those who followed them] (4).

Yet the distinction between the two kinds is evident. When one particular temporally originated thing is joined to another, the resulting perpetuity, extension, and persistence of the kind were not present in the individual instances. Thus, if the aggregate is long, extended, perpetual, numerous, and great, it does not follow that each individual instance must be long, extended, perpetual, numerous, and great. As for a series of causes and effects, each is possible, and joining it to another does not take it out of the realm of possibility. Each is also nonexistent, and joining it to another does not take it out—