Plato, Letters 344a

πέφυκεν, τὰ δὲ διέφθαρται, οὐδʼ ἂν ὁ Λυγκεὺς ἰδεῖν ποιήσειεν τοὺς τοιούτους. ἑνὶ δὲ λόγῳ, τὸν μὴ συγγενῆ τοῦ πράγματος οὔτʼ ἂν εὐμάθεια ποιήσειέν ποτε οὔτε μνήμη— τὴν ἀρχὴν γὰρ ἐν ἀλλοτρίαις ἕξεσιν οὐκ ἐγγίγνεται—ὥστε ὁπόσοι τῶν δικαίων τε καὶ τῶν ἄλλων ὅσα καλὰ μὴ προσφυεῖς εἰσιν καὶ συγγενεῖς, ἄλλοι δὲ ἄλλων εὐμαθεῖς ἅμα καὶ μνήμονες, οὐδʼ ὅσοι συγγενεῖς, δυσμαθεῖς δὲ καὶ ἀμνήμονες, οὐδένες τούτων μήποτε μάθωσιν ἀλήθειαν ἀρετῆς εἰς

morals is either naturally bad or else corrupted,—then not even Lynceus himself could make such folk see. In one word, neither receptivity nor memory will ever produce knowledge in him who has no affinity with the object, since it does not germinate to start with in alien states of mind; consequently neither those who have no natural connection or affinity with things just, and all else that is fair, although they are both receptive and retentive in various ways of other things, nor yet those who possess such affinity but are unreceptive and unretentive—none, I say, of these will ever learn to the utmost possible extent