Speusippus Biography

Athenian philosopher, son of Eurymedon and of Plato's sister Potone. He accompanied Plato on his last visit to Sicily (361) and succeeded him as head of the Academy from 347 to 339. Of his voluminous writings (Diog. Laert. 4. 4) only fragments and later reports remain, but Aristotle treats him with respect and it is clear that he continued and helped to shape some major philosophical interests which the Academy had acquired under Plato.

(a) DEFINITION Speusippus argued that, since a definition is designed to identify its subject and differentiate it from everything else, it can only be established by knowing everything there is. This can hardly have been intended, as some ancient critics thought, to refute all attempts at defining. More probably it was this view of definition which prompted Speusippus in his ten books of Homoia (‘Similar Things’) to set about collecting the observable resemblances between different sorts of plant and animal, for he may have thought (as Aristotle sometimes did, An. Post. B 13) that a species can be defined by discovering a set of characteristics which it shares with various other species, taken collectively, but not with any one other species.

The Academy's interest in definition had led to the recognition that some expressions have more than one meaning. Speusippus marked this by drawing distinctions comparable to, but fuller than, those familiar from Aristotle's logic. Where a single word is in question, it may have one sense or more than one (synōnyma, homōnyma); where more than one word is in question, they may stand for one thing or for quite different things, or one may derive its sense from the other (polyōnyma, heterōnyma, parōnyma). This in itself would give Speusippus his place at the birth of logic in the Academy.

(b) PHILOSOPHY AND EXACT SCIENCE Speusippus wrote on Pythagorean mathematics (see PYTHAGORAS), endorsing the search for the elements of numbers which Plato had taken over from the Pythagoreans (see the newly discovered fragment of Speusippus, Plato Latinus 3. 40 1–5). But he refused to equate numbers with Platonic Ideas, which like others in the Academy he rejected; and he further denied the claim, which Aristotle ascribes to the Pythagoreans and Plato, that the elements of number are the elements of everything else. Other sorts and levels of reality, he argued, need other sorts of element. Hence Aristotle accuses him of making the universe ‘episodic’, disconnected; but it is Speusippus' theory that underlies Aristotle's attempt in Metaph. A to show that it is not strictly true, but only true ‘by analogy’, that all things have the same elements.

(c) ETHICS In the Academic debate which can be heard behind Plato's Philebus and the ethical writings of Aristotle Speusippus makes two appearances. He holds, first, that pleasure is neither good nor evil in itself, and second, that goodness is to be found only in the final stages of development and not in the origins.

Under all these heads it is likely that the best of his work has been digested in that of Aristotle and his successors, and in particular that his biological observations in the Homoia were largely absorbed in the treatises of the Lyceum.

Gwilym Ellis Lane Owen; Simon Hornblower