Xenocrates (died 314 bc, Athens) was a Greek philosopher, pupil of Plato, and successor of Speusippus as the head of the Greek Academy, which Plato founded about 387 bc. In the company of Aristotle he left Athens after Plato’s death in 348/347, returning in 339 on his election as head of the Academy, where he remained until his death.
Xenocrates’ writings are lost except for fragments, but his doctrines appear to resemble Plato’s as reported by Aristotle. Among them is the “derivation” of all reality from the interaction of two opposite principles, “the One” and “the indeterminate dyad.” It is the dyad that is responsible for multiplicity, or diversity, evil, and motion, whereas the One is responsible for unity, good, and rest. Numbers and geometrical magnitudes are seen as the first products of this derivation. In addition Xenocrates divided all of reality into three realms: (1) the sensibles, or objects of sensation; (2) the intelligibles, or objects of true knowledge, such as Plato’s “Ideas”; and (3) the bodies of the heavens, which mediate between the sensibles and the intelligibles and are therefore objects of “opinion.” This tripartite division typifies the Academy’s tendency to bridge the gap between the two traditional modes of cognition, the mode of sense experience and the mode of intellection.
A second threefold division in Xenocrates’ thought separated gods, men, and “demons.” The demons represented semihuman, semidivine beings, some good and others evil. To these beings Xenocrates attributed much of what popular religion attributed to gods, and ritual mysteries were instituted to propitiate them, especially the evil ones. Though it is uncertain how literally Xenocrates viewed the demons, his demonology was highly influential, particularly on those early Christian writers who identified pagan deities with evil demons.
The classical distinction differentiating mind, body, and soul has been attributed by some to Xenocrates and by others to the Stoic philosopher Poseidonius. The same is true of the related doctrine that men die twice, the second time occurring on the Moon and consisting in the mind’s separation from the soul to make its ascent to the Sun. Sometimes considered an Atomist for his view that matter is composed of indivisible units, he held that Pythagoras, who stressed the importance of numbers in philosophy, was responsible for the Atomist view of acoustics, in which the sound perceived as a single entity actually consists of discrete sounds. The same Pythagorean influence on thinkers of the Academy can be seen in Xenocrates’ devotion to tripartite divisions. Yet another such division is found in his general view of philosophy, which he divided into logic, physics, and ethics. The origin of philosophy, he maintained, lies in man’s desire to resolve his anxieties. Happiness is defined as the acquisition of the perfection that is peculiar and proper to man; thus, enjoyment consists in being in contact with the things that are natural to him. This doctrine, which suggests the primacy of ethics over speculation in philosophy, foreshadows the Stoic view that ethical norms are to be derived from observation of the natural world. Xenocrates admitted, however, that external items are important for happiness, a notion that the Stoics rejected.