Plato, Laws 668c

καὶ ἀπεικασία· καὶ τοῦτό γε μῶν οὐκ ἂν σύμπαντες ὁμολογοῖεν ποιηταί τε καὶ ἀκροαταὶ καὶ ὑποκριταί; καὶ μάλα. δεῖ δὴ καθʼ ἕκαστόν γε, ὡς ἔοικε, γιγνώσκειν τῶν ποιημάτων ὅτι ποτʼ ἐστὶν τὸν μέλλοντα ἐν αὐτῷ μὴ ἁμαρτήσεσθαι· μὴ γὰρ γιγνώσκων τὴν οὐσίαν, τί ποτε βούλεται καὶ ὅτου ποτʼ ἐστὶν εἰκὼν ὄντως, σχολῇ τήν γε ὀρθότητα τῆς βουλήσεως ἢ καὶ ἁμαρτίαν αὐτοῦ διαγνώσεται. σχολῇ· πῶς δʼ οὔ;

imitative and representative; that much, at least, they would all admit,—poets, audience, and actors alike, would they not? They would. Now the man who is to judge a poem unerringly must know in each particular case the exact nature of the poem; for if he does not know its essence,—what its intention is and what the actual original which it represents,—then he will hardly be able to decide how far it succeeds or fails in fulfilling its intention. Hardly, to be sure.