Plato, Laws 670d

τρόπον ἀναγκάζομεν ᾄδειν, μέχρι γε τοσούτου πεπαιδεῦσθαι σχεδὸν ἀναγκαῖον, μέχρι τοῦ δυνατὸν εἶναι συνακολουθεῖν ἕκαστον ταῖς τε βάσεσιν τῶν ῥυθμῶν καὶ ταῖς χορδαῖς ταῖς τῶν μελῶν, ἵνα καθορῶντες τάς τε ἁρμονίας καὶ τοὺς ῥυθμούς, ἐκλέγεσθαί τε τὰ προσήκοντα οἷοί τʼ ὦσιν ἃ τοῖς τηλικούτοις τε καὶ τοιούτοις ᾄδειν πρέπον, καὶ οὕτως ᾄδωσιν, καὶ ᾄδοντες αὐτοί τε ἡδονὰς τὸ παραχρῆμα ἀσινεῖς ἥδωνται καὶ τοῖς νεωτέροις

and compelling, so to say, of their own free will to sing) must almost necessarily be trained up to such a point that every one of them may be able to follow both the steps of the rhythms and the chords of the tunes, so that, by observing the harmonies and rhythms, they may be able to select those of an appropriate kind, which it is seemly for men of their own age and character to sing, and may in this wise sing them, and in the singing may not only enjoy innocent pleasure themselves at the moment, but also may serve as leaders to the younger men in their seemly adoption of noble manners.