 One of the more elaborate philosophical discussions in the Doubts about Galen comes early in the work, and is devoted to the eternity of the world (this section is translated in PWL). Al-Rāzī here takes issue with Galen’s suggestion that empirical observation shows that the world was not created after not existing. Galen’s idea, based on a passage in Aristotle (On the Heavens 1.3, 270b11–16), is that the universe seems to be unchanging in its general features. If it is unchanging then it is not liable to corruption, and what is incorruptible is also ungenerable. Thus the universe has always existed, and always will. Al-Rāzī has little difficulty poking holes in this argument: he points out that the universe could be unchanging for a long time, and then be destroyed all at once, like a glass being smashed or a building collapsing when previously solid ground under it gives way (al-Rāzī, DG: §2.3). Furthermore, the incorruptibility of the universe would not be guaranteed by its lacking a natural tendency to decay. One also needs to rule out that there is some external cause that could destroy it (al-Rāzī, DG: §2.5). As often in the Doubts, al-Rāzī is here not trying to show that Galen’s conclusion is wrong—though in this case, we know that he thinks it is wrong—but that the argument offered for the conclusion is not sufficient. Ironically, this seems to be in accord with Galen’s own original intention. Galen’s argument is taken from his On Demonstration and was actually offered as an example of a proof that is not demonstrative (Koetschet 2015). Al-Rāzī is either being remarkably contentious, or has lost sight of the context of the argument: he even accuses Galen of being inconsistent, as he elsewhere states that it cannot be proven whether or not the universe is eternal.