Plato, Republic, book 5 724:

τούτων δὴ ὑποκειμένων λεγέτω μοι, φήσω, καὶ ἀποκρινέσθω ὁ χρηστὸσ ὃσ αὐτὸ μὲν καλὸν καὶ ἰδέαν τινὰ αὐτοῦ κάλλουσ μηδεμίαν ἡγεῖται ἀεὶ μὲν κατὰ ταὐτὰ ὡσαύτωσ ἔχουσαν, πολλὰ δὲ τὰ καλὰ νομίζει, ἐκεῖνοσ ὁ φιλοθεάμων καὶ οὐδαμῇ ἀνεχόμενοσ ἄν τισ ἓν τὸ καλὸν φῇ εἶναι καὶ δίκαιον καὶ τἆλλα οὕτω.