Οὐκοῦν ὅταν μέν τις μουσικῇ παρέχῃ καταυλεῖν καὶ καταχεῖν τῆς ψυχῆς διὰ τῶν ὤτων ὥσπερ διὰ χώνης ἃς νῦν δὴ ἡμεῖς ἐλέγομεν τὰς γλυκείας τε καὶ μαλακὰς καὶ θρηνώδεις ἁρμονίας, καὶ μινυρίζων τε καὶ γεγανωμένος ὑπὸ τῆς ᾠδῆς διατελῇ τὸν βίον ὅλον, οὗτος τὸ μὲν πρῶτον, εἴ τι θυμοειδὲς εἶχεν, ὥσπερ σίδηρον ἐμάλαξε καὶ χρήσιμον ἐξ ἀχρήστου καὶ σκληροῦ ἐποίησεν· ὅταν δ’ ἐπέχων μὴ ἀνίῃ ἀλλὰ κηλῇ, τὸ μετὰ τοῦτο ἤδη τήκει καὶ λείβει, ἕως ἂν ἐκτήξῃ τὸν θυμὸν καὶ ἐκτέμῃ ὥσπερ νεῦρα ἐκ τῆς ψυχῆς καὶ ποιήσῃ μαλθακὸν αἰχμητήν.
(Plato, Rep. 411a-b)
And, when a man allows music to play upon him and to pour into his soul through the funnel of his ears those sweet and soft and melancholy airs of which we were just now speaking, and his whole life is passed in warbling and the delights of song; in the first stage of the process the passion or spirit which is in him is tempered like iron, and made useful, instead of brittle and useless. But, if he carries on the softening and soothing process, in the next stage he begins to melt and waste, until he has wasted away his spirit and cut out the sinews of his soul; and he becomes a feeble warrior. (tr. Benjamin Jowett)