Plato, Laws 670c

ὅτι δὲ δρῶσιν ταῦτα ἀγνοοῦντες αὐτῶν ἕκαστα, οὐ συλλογίζονται. τὸ δέ που προσήκοντα μὲν ἔχον πᾶν μέλος ὀρθῶς ἔχει, μὴ προσήκοντα δὲ ἡμαρτημένως. ἀναγκαιότατα. τί οὖν ὁ μηδʼ ὅτι ποτʼ ἔχει γιγνώσκων; ἆρα, ὅπερ εἴπομεν, ὡς ὀρθῶς γε αὐτὸ ἔχει, γνώσεταί ποτε ἐν ὁτῳοῦν; καὶ τίς μηχανή; τοῦτʼ οὖν, ὡς ἔοικεν, ἀνευρίσκομεν αὖ τὰ νῦν, ὅτι τοῖς ᾠδοῖς ἡμῖν, οὓς νῦν παρακαλοῦμεν καὶ ἑκόντας τινὰ

in time; and they fail to comprehend that, in doing each of these things, they do them in ignorance. But the fact is that every tune which has its appropriate elements is correct, but incorrect if the elements are inappropriate. Undoubtedly. What then of the man who does not know in the least what the tune’s elements are? Will he ever know about any tune, as we said, that it is correct? There is no possible means of his doing so. We are now once more, as it appears, discovering the fact that these singers of ours (whom we are now inviting