Abstract

Aristotle divided the natural world into two realms: the celestial spheres of the heavens revolve eternally around the sublunary domain where the elements naturally rise and fall. The cosmos is structured by a contrast between two simple and irreducible kinds of motion, circular and rectilinear. A different view of circular motion seems to be offered in the little-studied Mechanica, attributed to Aristotle in the manuscript tradition but now usually seen as the work of a Peripatetic philosopher of the early third century BCE . The Mechanica understands motion on a circular path as the result of a combination of two rectilinear motions, but the details of this account remain unclear. What did this analysis aim to achieve? Is it based on mathematical or physical principles? Why is it difficult to read? To what extent did it clash with Aristotle’s views of the natural world? I shall address these questions, arguing that the Mechanica draws on the resources of geometry to support a basically physical agenda and to deliver a causal explanation.