 An accidental ordering takes place over time, as when rain comes from a cloud, the cloud comes from vapor, and vapor comes from a prior rain (Incoherence I.4 {268}). Such an ordering is circular, inasmuch as the materials from one stage are corrupted and reused in a later stage, and so there is no threat of an actual infinity. There is thus nothing incoherent about such a series extending infinitely far into the past and infinitely far into the future, and indeed Ibn Rushd argues that such an infinity can be proved in various ways (Davidson 1987). One fundamental proof arises from the nature of the First Cause. Since it is itself unmoved—that is, wholly changeless—its causal agency must likewise be eternal. “A thing lacking the potential for change and alteration cannot be changed at any time, since if it were then its alteration would be by cause of itself, and so there would be alteration without the possibility for it” (LongCaelo I.103). It is, for Ibn Rushd, incoherent to posit an eternally existing, changeless actuality, which suddenly springs into agency after having not acted for an eternity. In general, “the effect of a cause cannot be delayed after the causation” (Incoherence I.1 {15}). Similar considerations show that the world’s future existence must likewise be eternal (Incoherence 1.1 {22}).