Plato, Meno 73c

δίκαιοι; ναί. πάντες ἄρʼ ἄνθρωποι τῷ αὐτῷ τρόπῳ ἀγαθοί εἰσιν· τῶν αὐτῶν γὰρ τυχόντες ἀγαθοὶ γίγνονται. ἔοικε. οὐκ ἂν δήπου, εἴ γε μὴ ἡ αὐτὴ ἀρετὴ ἦν αὐτῶν, τῷ αὐτῷ ἂν τρόπῳ ἀγαθοὶ ἦσαν. οὐ δῆτα. ἐπειδὴ τοίνυν ἡ αὐτὴ ἀρετὴ πάντων ἐστίν, πειρῶ εἰπεῖν καὶ ἀναμνησθῆναι τί αὐτό φησι Γοργίας εἶναι καὶ σὺ μετʼ ἐκείνου. τί ἄλλο γʼ ἢ ἄρχειν οἷόν τʼ εἶναι τῶν ἀνθρώπων;

So all mankind are good in the same way; for they become good when they acquire the same qualities. So it seems. And I presume, if they had not the same virtue, they would not be good in the same way. No, indeed. Seeing then that it is the same virtue in all cases, try and tell me, if you can recollect, what Gorgias—and you in agreement with him—say it is. Simply that it is the power of governing mankind—