 Speusippus of Athens was the son of Plato’s sister Potone; he became head of the Academy on Plato’s death in 348/347 and remained its head for eight years (Diogenes Laertius iv 1), apparently until his death. His date of birth is harder to get a fix on; it has reasonably been estimated at ca. 410. He apparently wrote a lot: “a great many treatises and many dialogues” (ibid. iv 4; Diogenes lists about 30 titles, and his bibliography is on his own admission incomplete). We have very little of what he wrote, if any (we have something from a work later attributed to him, On Pythagorean Numbers, discussed below, but this is not one of Diogenes’ titles; and we may have something preserved in Iamblichus, De communi mathematica scientia iv, also discussed below).