Simple Motions, Simple Bodies and Aristotle’s Explanation of Locomotion in De Caelo I.2

The thesis of this paper is that, in De Caelo I.2, the introduction and differentiation of simple bodies is achieved entirely by differentiating simple motions. This runs counter to the traditional interpretations of De Caelo I.2, which consider how, and how completely, Aristotle uses the differentiation of simple magnitudes to differentiate simple bodies, and which assume that he introduces the notion of a simple body independently of the notion of a simple motion. But the traditional interpretations miss the point of Aristotle’s argument in De Caelo I.2, which – so I argue – is to introduce the notion of simple motions, using this to introduce the notion of simple bodies, and to thereby provide an explanatory account of all possible locomotion. This is the reason why Aristotle identifies simple bodies in De Caelo I.2 with the fundamental components of the universe.