Plato, Meno 79c

ἀρετῆς πράττηται, ὥσπερ εἰρηκὼς ὅτι ἀρετή ἐστιν τὸ ὅλον καὶ ἤδη γνωσομένου ἐμοῦ, καὶ ἐὰν σὺ κατακερματίζῃς αὐτὴν κατὰ μόρια. δεῖται οὖν σοι πάλιν ἐξ ἀρχῆς, ὡς ἐμοὶ δοκεῖ, τῆς αὐτῆς ἐρωτήσεως, ὦ φίλε Μένων, τί ἐστιν ἀρετή, εἰ μετὰ μορίου ἀρετῆς πᾶσα πρᾶξις ἀρετὴ ἂν εἴη; τοῦτο γάρ ἐστιν λέγειν, ὅταν λέγῃ τις, ὅτι πᾶσα ἡ μετὰ δικαιοσύνης πρᾶξις ἀρετή ἐστιν. ἢ οὐ δοκεῖ σοι πάλιν δεῖσθαι τῆς αὐτῆς ἐρωτήσεως, ἀλλʼ οἴει τινὰ εἰδέναι μόριον ἀρετῆς ὅτι ἐστίν, αὐτὴν μὴ εἰδότα; οὐκ ἔμοιγε δοκεῖ.

with a part of virtue; as though you had told me what virtue is in the whole, and I must understand it forthwith—when you are really splitting it up into fragments! I think therefore that you must face the same question all over again, my dear Meno—What is virtue?—if we are to be told that every action accompanied by a part of virtue is virtue; for that is the meaning of the statement that every action accompanied by justice is virtue. Or do you not agree that you have to meet the same question afresh? Do you suppose that anyone can know a part of virtue when he does not know virtue itself? No, I do not.