Plato, Meno 87d

ἔμοιγε δοκεῖ τοῦτο μετὰ τοῦτο σκεπτέον εἶναι. τί δὲ δή; ἄλλο τι ἢ ἀγαθὸν αὐτό φαμεν εἶναι τὴν ἀρετήν, καὶ αὕτη ἡ ὑπόθεσις μένει ἡμῖν, ἀγαθὸν αὐτὸ εἶναι; πάνυ μὲν οὖν. οὐκοῦν εἰ μέν τί ἐστιν ἀγαθὸν καὶ ἄλλο χωριζόμενον ἐπιστήμης, τάχʼ ἂν εἴη ἡ ἀρετὴ οὐκ ἐπιστήμη τις· εἰ δὲ μηδέν ἐστιν ἀγαθὸν ὃ οὐκ ἐπιστήμη περιέχει, ἐπιστήμην ἄν τινʼ αὐτὸ ὑποπτεύοντες εἶναι ὀρθῶς ὑποπτεύοιΜΕΝ. ἔστι ταῦτα. καὶ μὴν

I should say that is the next thing we have to consider. Well now, surely we call virtue a good thing, do we not, and our hypothesis stands, that it is good? Certainly we do. Then if there is some good apart and separable from knowledge, it may be that virtue is not a kind of knowledge; but if there is nothing good that is not embraced by knowledge, our suspicion that virtue is a kind of knowledge would be well founded. Quite so. Now it is by virtue that we are good? Yes.