Note 34 — Chapter XIII · HIPPIAS MAJOR — HIPPIAS MINOR.
Reading edition
Plat. Hipp. Maj. 303 E — 304 A. Οὔκουν ὠφέλιμον, φήσει, τὸ ποιοῦν τἀγαθόν, τὸ δὲ ποιοῦν καὶ τὸ ποιούμενον, ἕτερον νῦν δὴ ἐφάνη, καὶ εἰς τὸν πρότερον λόγον ἥκει ὑμῖν ὁ λόγος; οὔτε γὰρ τὸ ἀγαθὸν ἂν εἴη καλὸν οὔτε τὸ καλὸν ἀγαθόν, εἴπερ ἄλλο αὐτῶν ἑκάτερόν ἐστιν.
These last words deserve attention, because they coincide with the doctrine ascribed to Antisthenes, which has caused so many hard words to be applied to him (as well as to Stilpon) by critics, from Kolôtes downwards. The general principle here laid down by Plato is — A is something different from B, therefore A is not B and B is not A. In other words, A cannot be predicated of B nor B of A. Antisthenes said in like manner — Ἄνθρωπος and Ἀγαθὸς are different from each other, therefore you cannot say Ἄνθρωπος ἐστιν ἀγαθός. You can only say Ἄνθρωπος ἐστιν Ἄνθρωπος — Ἀγαθός ἐστιν ἀγαθός.
I have touched farther upon this point in my chapter upon Antisthenes and the other Viri Sokratici.