Plato, Meno 89d

τί οὖν δή; πρὸς τί βλέπων δυσχεραίνεις αὐτὸ καὶ ἀπιστεῖς μὴ οὐκ ἐπιστήμη ᾖ ἡ ἀρετή; ἐγώ σοι ἐρῶ, ὦ Μένων. τὸ μὲν γὰρ διδακτὸν αὐτὸ εἶναι, εἴπερ ἐπιστήμη ἐστίν, οὐκ ἀνατίθεμαι μὴ οὐ καλῶς λέγεσθαι· ὅτι δὲ οὐκ ἔστιν ἐπιστήμη, σκέψαι ἐάν σοι δοκῶ εἰκότως ἀπιστεῖν. τόδε γάρ μοι εἰπέ· εἰ ἔστιν διδακτὸν ὁτιοῦν πρᾶγμα, μὴ μόνον ἀρετή, οὐκ ἀναγκαῖον αὐτοῦ καὶ διδασκάλους καὶ μαθητὰς εἶναι; ἔμοιγε δοκεῖ.

Why, what reason have you to make a difficulty about it, and feel a doubt as to virtue being knowledge? I will tell you, Meno. I do not withdraw as incorrect the statement that it is taught, if it is knowledge; but as to its being knowledge, consider if you think I have grounds for misgiving. For tell me now: if anything at all, not merely virtue, is teachable, must there not be teachers and learners of it?