Plato, Letters 338d

Τάραντι καὶ Διονυσίῳ ποιήσας ἀπέπλεον—ἄλλοι τέ τινες ἐν Συρακούσαις ἦσαν Δίωνός τε ἄττα διακηκοότες καὶ τούτων τινὲς ἄλλοι, παρακουσμάτων τινῶν ἔμμεστοι τῶν κατὰ φιλοσοφίαν· οἳ δοκοῦσί μοι Διονυσίῳ πειρᾶσθαι διαλέγεσθαι τῶν περὶ τὰ τοιαῦτα, ὡς Διονυσίου πάντα διακηκοότος ὅσα διενοούμην ἐγώ. ὁ δὲ οὔτε ἄλλως ἐστὶν ἀφυὴς πρὸς τὴν τοῦ μανθάνειν δύναμιν φιλότιμός τε θαυμαστῶς· ἤρεσκέν τε οὖν ἴσως αὐτῷ τὰ λεγόμενα ᾐσχύνετό τε φανερὸς γιγνόμενος

and there were certain others in Syracuse who had had some teaching from Dion, and others again who had been taught by these, men who were stuffed with some borrowed philosophical doctrines. These men, I believe, tried to discuss these subjects with Dionysius, on the assumption that Dionysius was thoroughly instructed in all my system of thought. Now besides being naturally gifted otherwise with a capacity for learning Dionysius has an extraordinary love of glory. Probably, then, he was pleased with what was said and was ashamed of having it known that he had no lessons