Speusippus spyo͞osĭpˈəs [key], fl. 347–339 b.c., Greek philosopher; disciple and nephew of Plato, whom he succeeded as head of the Academy. Speusippus distinguished 10 grades of being, thereby prefiguring Neoplatonism. He held that the good is not the source of being but is its goal. One of his most significant ideas is that it is impossible to have satisfactory knowledge of anything without knowing all things besides. A portion of his writings on Pythagorean numbers has survived.

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