Xenocrates (zĬnŏk´rətēz), 396–314 BC, Greek philosopher, b. Chalcedon, successor of Speusippus as head of the Academy. He was a disciple of Plato, whom he accompanied to Sicily in 361 BC His ascetic life and noble character greatly influenced his pupils. He was the first to divide philosophy into dialectic (or logic), physics, and ethics, the latter two being his principal themes. He held that mathematical objects and the Platonic Ideas are both substances, and both identical, causing Aristotle to say of him that he "made ideal and mathematical number the same." His Platonic ethics taught that virtue produces happiness, although external goods can contribute. Only fragments of his work survive.