Xenocrates (zəˈnɒkrəˌtiːz; Ξενοκράτης; c. 396/5 - 314/3 BC) of Chalcedon was a Greek philosopher, mathematician, and leader (scholarch) of the Platonic Academy from 339/8 to 314/3 BC. His teachings followed those of Plato, which he attempted to define more closely, often with mathematical elements. He distinguished three forms of being: the sensible, the intelligible, and a third compounded of the two, to which correspond respectively, sense, intellect and opinion. He considered unity and duality to be gods which rule the universe, and the soul a self-moving number. God pervades all things, and there are daemonical powers, intermediate between the divine and the mortal, which consist in conditions of the soul. He held that mathematical objects and the Platonic Ideas are identical, unlike Plato who distinguished them. In ethics, he taught that virtue produces happiness, but external goods can minister to it and enable it to effect its purpose.
Xenocrates was a native of Chalcedon. By the most probable calculation he was born 396/5 BC, and died 314/3 BC at the age of 82. His father was named Agathon (Ἀγάθωνος) or Agathanor (Ἀγαθάνορος).
Moving to Athens in early youth, he became the pupil of Aeschines Socraticus, but subsequently joined himself to Plato, whom he accompanied to Sicily in 361. Upon his master's death, he paid a visit with Aristotle to Hermias of Atarneus. In 339/8 BC, Xenocrates succeeded Speusippus in the presidency of the school, defeating his competitors Menedemus of Pyrrha and Heraclides Ponticus by a few votes. On three occasions he was member of an Athenian legation, once to Philip, twice to Antipater.
Xenocrates resented the Macedonian influence then dominant at Athens. Soon after the death of Demosthenes (c. 322 BC), he declined the citizenship offered to him at the insistence of Phocion as a reward for his services in negotiating peace with Antipater after Athens' unsuccessful rebellion.