It might seem quite commonplace to say that Aristotle identifies fire, air, water and earth as the στοιχεῖα, or ‘elements’ – or, to be more precise, as the elements of bodies that are subject to generation and corruption. Yet there is a tradition of interpretation, already evident in the work of the sixth-century commentator John Philoponus and widespread, indeed prevalent, today, according to which Aristotle does not really believe that fire, air, water and earth are truly elemental. The basic premise of this interpretation is that Aristotle takes fire, air, water and earth to be, in some sense, composite bodies and, as such, analysable into simpler constituents. But, of course, an element of bodies is defined by Aristotle himself as something into which bodies can be analysed, and which does not admit further analysis (Metaph. 5.3, 1014a26–1014b15; Cael. 3.3, 302a14–21). So if fire, air, water and earth can be analysed into simpler or more basic constituents, then it would seem to follow that the latter ought to be considered Aristotle's true elements. These are usually identified as the primary contraries hot and cold, dry and wet; many, perhaps most, commentators would insist also upon prime matter as the subject upon which these contraries act.