Plato, Laws 669b

πρῶτον γιγνώσκειν, ἔπειτα ὡς ὀρθῶς, ἔπειθʼ ὡς εὖ, τὸ τρίτον, εἴργασται τῶν εἰκόνων ἡτισοῦν ῥήμασί τε καὶ μέλεσι καὶ τοῖς ῥυθμοῖς; ἔοικε γοῦν. μὴ τοίνυν ἀπείπωμεν λέγοντες τὸ περὶ τὴν μουσικὴν ᾗ χαλεπόν· ἐπειδὴ γὰρ ὑμνεῖται περὶ αὐτὴν διαφερόντως ἢ τὰς ἄλλας εἰκόνας, εὐλαβείας δὴ δεῖται πλείστης πασῶν εἰκόνων. ἁμαρτών τε γάρ τις μέγιστʼ ἂν βλάπτοιτο,

first, a knowledge of the nature of the original; next, a knowledge of the correctness of the copy; and thirdly, a knowledge of the excellence with which the copy is executed? It would seem so, certainly. Let us not hesitate, then, to mention the point wherein lies the difficulty of music. Just because it is more talked about than any other form of representation, it needs more caution than any. The man who blunders in this art will do himself the greatest harm, by welcoming base morals;