This essay explores the role that GC II 10 plays in the context of the treatise as a whole. It argues that while the rest of the treatise, up to and including GC II 9, explains generation and perishing by means of material and formal causes, GC II 10 provides the efficient and final causes, and thus brings the project announced at the outset of GC to completion. The essay analyses the arguments for the efficient cause of generation and corruption (identified with the sun’s annual course along the ecliptic) and its final cause (identified with a universal desire for the highest kind of being). For Aristotle, the best approximation to the being of imperishable substance which the sublunary sphere permits, given the nature of its constituents, is perpetual reproduction (for living things) and an endless cycle of reciprocal change (for elements). Finally, the essay illustrates how Aristotle’s fourfold scheme of causal explanations practically applies to generation and perishing in view of what Aristotle claims elsewhere about the unmoved mover and the gradation of being.