In GC II 3, Aristotle gives an initial justification of three theses: (i) that there are four primary bodies; (ii) that these are earth, air, fire, and water; and (iii) that each is associated with two primary differentiae. Despite his laconic presentation, Aristotle offers an impressive variety of justifications for his main contentions: he appeals to combinatorial mathematics, to what is “in accordance with argument,” to empirical observation, and to his predecessors. I consider whether this chapter indicates that the primary bodies are not really elements; whether the “apparent simple bodies” Aristotle mentions are the primary bodies or something else; and how to understand the “fiery” and “airy” things that are not fire and air (respectively) but somehow like them. I find that the primary bodies are indeed genuine elements of sensible bodies for Aristotle; that the “apparent simple bodies” are the everyday counterparts of the elemental bodies; and that the contrast between fiery and airy things and fire and air is a contrast between the elemental bodies and their everyday counterparts.

This essay provides an analysis of GC I and explains why we now need to investigate the “so-called elements” – the primary bodies that make up all the more complex bodies of the sublunary world. This is an important passage for understanding how the discussion of the elements fits into the overall program of the whole work. In the second section, Aristotle broaches the question of whether there is a kind of matter “beyond” these elements. He criticizes two earlier theories which (he thinks) give an affirmative answer to this question: Anaximander’s theory of the apeiron and Plato’s theory of the Receptacle in the Timaeus. In the final section, Aristotle sets out his own position. This section is evidence that he was committed to prime matter – an ultimate material substratum which partially constitutes each of the primary sublunary bodies, and which underlies the process of elemental inter-transformation.