SPEUSIPPUSAthens, 339 B.C.
Ancient Greek philosopher, head of the Platonic Academy after Plato's death (347 BC). Speusippus, Plato's nephew and student, had accompanied him on his trip to Sicily in 361 BC. He was also an advocate of cooperativism, on behalf of his uncle, of political figures, including Dionysius II of Syracuse.
From the philosophical texts of Speusippus, some passages, his references to other authors and above all an extensive part of his work on Pythagorean numbers have been preserved. Like many of his contemporaries and immediate successors in the newly-formed Academy, Speusippus emphasized the importance of numbers and numerical combinations and downplayed the importance of ideas. In the passage, for example, from his work on numbers, the special meaning - derived from its "perfection" - of the number ten is explained.
According to what is mentioned by Aristotle, which is often judged to be inaccurate in the points mentioned in Plato, Speysippus adopted the Platonic doctrine according to which all things originate achronically from two opposite principles, "One" and the indeterminate "duality" as principles of good and evil respectively. However, Speusippos denied attributing moral values to them. He organized reality using numerical terms, into ten progressively deflating spheres. Between the spheres of real numbers ("mathematical") and those of the body ("sensible") he placed the sphere of the soul, all parts of which he considered immortal. Aristotle strongly criticizes Speussippus, but Speussippus's "Similar" (a comparative study of plant and animal physiology) is aptly compared to Aristotle's own On the histories of Animals, and probably echoes Speussippus' view that nothing can be defined unless everything is defined at the same time, because classification and definition are directly connected.