Plato, Epinomis 989d

ἀρετήν, ὃ δὴ καὶ μέγιστόν ἐστι συμπάντων πάσῃ τῇ πόλει. τοῦτο δὴ οὖν τὸ μέρος εἶναί φαμεν φύσει κυριώτατον καὶ δυνατὸν ὡς οἷόν τε κάλλιστα καὶ ἄριστα μαθεῖν, εἰ διδάσκοι τις. ἀλλʼ οὐδʼ ἂν διδάξειεν, εἰ μὴ θεὸς ὑφηγοῖτο· εἰ τʼ οὖν διδάσκοι, κατὰ τρόπον δὲ μὴ δρῷ τὸ τοιοῦτον, κρεῖττον μὴ μανθάνειν. ὅμως δʼ ἐκ τῶν νῦν λεγομένων ἀνάγκη μαθεῖν ταῦτα καὶ ἐμὲ λέγειν τὴν τοιαύτην τε καὶ ἀρίστην φύσιν.

but truly honoring virtue, which indeed is the most important of all business for the whole state. That section of us, then, we say is naturally the most competent, and supremely able to learn the best and noblest lessons that it may be taught: but it cannot get this teaching either, unless God gives his guidance. If, however, it should be so taught, but should fail in some way to do accordingly, it were better for it not to learn. Nevertheless it follows of necessity from our present statements, that I agree that the nature which is of this kind, and the best, should learn certain things.