Xenarchus (3) of Seleucia, Peripatetic philosopher, c. 30 BCE

Xenarchus taught at Alexandria, Athens, and Rome, and his acquaintances included the geographer Strabo and the emperor Augustus. He is best known for his critique of Aristotle’s fifth element, which constitutes the material of the heavenly bodies according to the De caelo. Xenarchus targeted in particular Aristotle’s reliance on direct correspondences between simple bodies and simple motions and suggested that the ontologically privileged fire “in its natural place” could perform circular motion and was thus a plausible candidate for the material constituent of the heavens. He made further contributions in physics, psychology, and ethics, but he does not seem to have shown the same interest in the Categories as his Peripatetic contemporaries.