Plato, Laws 668d

ὁ δὲ τὸ ὀρθῶς μὴ γιγνώσκων ἆρʼ ἄν ποτε τό γε εὖ καὶ τὸ κακῶς δυνατὸς εἴη διαγνῶναι; λέγω δὲ οὐ πάνυ σαφῶς, ἀλλʼ ὧδε σαφέστερον ἴσως ἂν λεχθείη. πῶς; εἰσὶν δήπου κατὰ τὴν ὄψιν ἡμῖν ἀπεικασίαι μυρίαι. ναί. τί οὖν εἴ τις καὶ ἐν τούτοις ἀγνοοῖ τῶν μεμιμημένων ὅτι ποτʼ ἐστὶν ἕκαστον τῶν σωμάτων; ἆρʼ ἄν ποτε τό γε ὀρθῶς αὐτῶν εἰργασμένον γνοίη; λέγω δὲ τὸ τοιόνδε, οἷον τοὺς ἀριθμοὺς τοῦ σώματος καὶ ἑκάστων τῶν μερῶν

And would a man who does not know what constitutes perfection be able to decide as to the goodness or badness of a poem? But I am not making myself quite clear: it might be clearer if I put it in this way— In what way? As regards objects of sight we have, of course, thousands of representations. Yes. How, then, if in this class of objects a man were to be ignorant of the nature of each of the bodies represented could he ever know whether it is perfectly executed? What I mean is this: whether it preserves the proper dimensions and the positions of each of the bodily parts,