Speusippus

Speusippus was the son of Plato's sister Potone and succeeded his uncle as head of the Academy on his death in 347 BCE, leading it for some eight years until his own death. He accompanied Plato on his last journey to Sicily. Only fragments of his many writings survive, but enough to show that he revised his uncle's teaching in a markedly mathematical direction.

He appears to have abandoned the Forms as Plato had conceived them, treating mathematical objects — numbers and magnitudes — as the fundamental realities instead. He also held that the first principle, the One, is so far above being that it cannot yet be called good or beautiful, since goodness and beauty emerge only later as things develop, like the flower from the seed. This austere conception of a first principle beyond even goodness strikingly anticipates the later Neoplatonist insistence that the One lies beyond all attributes.

His leadership marks the beginning of the Academy's long internal development, in which Plato's heirs — Speusippus, Xenocrates, and their successors — debated, systematized, and recast the master's thought rather than simply repeating it.