Plato, Meno 98d

οὔτε ἐπιστήμη οὔτε δόξα ἀληθής, ἐπίκτητα—ἢ δοκεῖ σοι φύσει ὁποτερονοῦν αὐτοῖν εἶναι; οὐκ ἔμοιγε. οὐκοῦν ἐπειδὴ οὐ φύσει, οὐδὲ οἱ ἀγαθοὶ φύσει εἶεν ἄν. οὐ δῆτα. ἐπειδὴ δέ γε οὐ φύσει, ἐσκοποῦμεν τὸ μετὰ τοῦτο εἰ διδακτόν ἐστιν. ναί. οὐκοῦν διδακτὸν ἔδοξεν εἶναι, εἰ φρόνησις ἡ ἀρετή; ναί. κἂν εἴ γε διδακτὸν εἴη, φρόνησις ἂν εἶναι; πάνυ γε.

and true opinion—is a natural property of mankind, being acquired—or do you think that either of them is natural? Not I. Then if they are not natural, good people cannot be good by nature either. Of course not. And since they are not an effect of nature, we next considered whether virtue can be taught. Yes. And we thought it teachable if virtue is wisdom? Yes. And if teachable, it must be wisdom? Certainly. And if there were teachers, it could be taught,