Plato, Laws 669a

καὶ χρώματα ἅμα καὶ σχήματα ἀπείληφεν ὑπὸ τῆς τέχνης; ἆρά γε ἀναγκαῖον ἤδη τῷ ταῦτα γνόντι καὶ ἐκεῖνο ἑτοίμως γιγνώσκειν, εἴτε καλὸν εἴτε ὅπῃ ποτὲ ἐλλιπὲς ἂν εἴη κάλλους; πάντες μεντἂν ὡς ἔπος εἰπεῖν, ὦ ξένε, τὰ καλὰ τῶν ζῴων ἐγιγνώσκομεν. ὀρθότατα λέγεις. ἆρʼ οὖν οὐ περὶ ἑκάστην εἰκόνα, καὶ ἐν γραφικῇ καὶ ἐν μουσικῇ καὶ πάντῃ, τὸν μέλλοντα ἔμφρονα κριτὴν ἔσεσθαι δεῖ ταῦτα τρία ἔχειν, ὅ τέ ἐστι

and shapes,—is it at once inevitable that the person who knows this can easily discern also whether the work is beautiful, or wherein it is deficient in beauty? If that were so, Stranger, practically all of us would know what animals are beautiful. You are quite right. In regard, then, to every representation—whether in painting, music or any other art—must not the judicious critic possess these three requisites: