Plato, Meno 92c

πῶς οὖν ἄν, ὦ δαιμόνιε, εἰδείης περὶ τούτου τοῦ πράγματος, εἴτε τι ἀγαθὸν ἔχει ἐν αὑτῷ εἴτε φλαῦρον, οὗ παντάπασιν ἄπειρος εἴης; ῥᾳδίως· τούτους γοῦν οἶδα οἵ εἰσιν, εἴτʼ οὖν ἄπειρος αὐτῶν εἰμι εἴτε μή. μάντις εἶ ἴσως, ὦ Ἄνυτε· ἐπεὶ ὅπως γε ἄλλως οἶσθα τούτων πέρι, ἐξ ὧν αὐτὸς λέγεις θαυμάζοιμʼ ἄν. ἀλλὰ γὰρ οὐ τούτους ἐπιζητοῦμεν τίνες εἰσίν, παρʼ οὓς ἂν

And trust I never may. How then, my good sir, can you tell whether a thing has any good or evil in it, if you are quite without experience of it? Easily: the fact is, I know what these people are, whether I have experience of them or not. You are a wizard, perhaps, Anytus; for I really cannot see, from what you say yourself, how else you can know anything about them. But we are not inquiring now who the teachers are