Xenocrates (; ; c. 396/5314/3 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.
Life
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 () or Agathanor ().
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. The settlement was reached "at the price of a constitutional change: thousands of poor Athenians were disenfranchised," and Xenocrates said "that he did not want to become a citizen within a constitution he had struggled to prevent". Being unable to pay the tax levied upon resident aliens, he is said to have been saved only by the courage of the orator Lycurgus, or even to have been bought by Demetrius Phalereus, and then emancipated. In 314/3, he died from hitting his head, after tripping over a bronze pot in his house.
Xenocrates was succeeded as scholarch by Polemon, whom he had reclaimed from a life of profligacy. Besides Polemon, the statesman Phocion, Chaeron (tyrant of Pellene), the academic Crantor, the Stoic Zeno and Epicurus are said to have frequented his lectures.
Wanting in quickness of apprehension and natural grace he compensated by persevering and thorough-going industry, pure benevolence, purity of morals, unselfishness, and a moral earnestness, which compelled esteem and trust even from the Athenians of his own age.
Xenocrates adhered closely to the Platonist doctrine, and he is accounted the typical representative of the Old Academy. In his writings, which were numerous, he seems to have covered nearly the whole of the Academic program; but metaphysics and ethics were the subjects which principally engaged his thoughts. He is said to have made more explicit the division of philosophy into the three parts of Physics, Dialectic and Ethics.
When Alexander the Great sent him 30 talents of gold, he sent it back, saying that a king, not a philosopher, needs money.
Writings
With a comprehensive work on Dialectic () there were also separate treatises On Knowledge, On Knowledgibility (), On Divisions (), On Genera and Species (), On Ideas (), On the Opposite (), and others, to which probably the work On Mediate Thought () also belonged. Two works by Xenocrates on Physics are mentioned (), as are also books On the Gods (), On the Existent (), On the One (), On the Indefinite (), On the Soul (), On the Emotions () On Memory (), etc. In like manner, with the more general Ethical treatises On Happiness (), and On Virtue () there were connected separate books on individual Virtues, on the Voluntary, etc. His four books on Royalty he had addressed to Alexander (). Besides these he had written treatises On the State (), On the Power of Law (), etc., as well as upon Geometry, Arithmetic, and Astrology. Besides philosophical treatises, he wrote poetry () and paraenesis.