Plato, Laws 654d

τῷ σώματι μὴ πάνυ δυνατὸς ᾖ κατορθοῦν, ἢ διανοεῖσθαι, τῇ δὲ ἡδονῇ καὶ λύπῃ κατορθοῖ, τὰ μὲν ἀσπαζόμενος, ὅσα καλά, τὰ δὲ δυσχεραίνων, ὁπόσα μὴ καλά; πολὺ τὸ διαφέρον, ὦ ξένε, λέγεις τῆς παιδείας. οὐκοῦν εἰ μὲν τὸ καλὸν ᾠδῆς τε καὶ ὀρχήσεως πέρι γιγνώσκομεν τρεῖς ὄντες, ἴσμεν καὶ τὸν πεπαιδευμένον τε καὶ ἀπαίδευτον ὀρθῶς· εἰ δὲ ἀγνοοῦμέν γε τοῦτο, οὐδʼ εἴ τις παιδείας ἐστὶν φυλακὴ καὶ ὅπου διαγιγνώσκειν ἄν ποτε

he yet keeps right in his feelings of pain and pleasure, welcoming everything good and abhorring everything not good. There is a vast difference between the two cases, Stranger, in point of education. If, then, we three understand what constitutes goodness in respect of dance and song, we also know who is and who is not rightly educated but without this knowledge we shall never be able to discern whether there exists any safeguard for education