[20] Aristotle, de An. 430b 5, and generally iii. 2, iii. 5.
[21] For Plato’s Logic, the controversies as to the genuineness of the dialogues may be treated summarily. The Theaetetus labours under no suspicion. The Sophistes is apparently matter for animadversion by Aristotle in the Metaphysics and elsewhere, but derives stronger support from the testimonies to the Politicus which presumes it. The Politicus and Philebus are guaranteed by the use made of them in Aristotle’s Ethics. The rejection of the Parmenides would involve the paradox of a nameless contemporary of Plato and Aristotle who was inferior as a metaphysician to neither. No other dialogue adds anything to the logical content of these.
Granted their genuineness, the relative dating of three of them is given, viz. Theaetetus, Sophistes and Politicus in the order named. The Philebus seems to presuppose Politicus, 283-284, but if this be an error, it will affect the logical theory not at all. There remains the Parmenides. It can scarcely be later than the Sophistes. The antinomies with which it concludes are more naturally taken as a prelude to the discussion of the Sophistes than as an unnecessary retreatment of the doctrine of the one and the many in a more negative form. It may well be earlier than the Theaetetus in its present form. The stylistic argument shows the Theaetetus relatively early. The maturity of its philosophic outlook tends to give it a place relatively advanced in the Platonic canon. To meet the problem here raised, the theory has been devised of an earlier and a later version. The first may have linked on to the series of Plato’s dialogues of search, and to put the Parmenides before it is impossible. The second, though it might still have preceded the Parmenides might equally well have followed the negative criticism of that dialogue, as the beginning of reconstruction. For Plato’s logic this question only has interest on account of the introduction of an Ἀριστοτέλης in a non-speaking part in the Parmenides. If this be pressed as suggesting that the philosopher Aristotle was already in full activity at the date of writing, it is of importance to know what Platonic dialogues were later than the début of his critical pupil.
On the stylistic argument as applied to Platonic controversies Janell’s Quaestiones Platonicae (1901) is important. On the whole question of genuineness and dates of the dialogues, H. Raeder, Platons philosophische Entwickelung (1905), gives an excellent conspectus of the views held and the grounds alleged. See also [Plato].
[22] E.g. that of essence and accident. Republic, 454.
[23] E.g. the discussion of correlation, ib. 437 sqq.
[24] Politicus, 285d.
[25] Sophistes, 261c sqq.
[26] E.g. in Nic. Eth. i. 6.
[27] Philebus, 16d.