Plato, Letters 345b

ἅπαξ, οὕτως εἰδέναι τε οἴεται καὶ ἱκανῶς οἶδεν, εἴτε αὐτὸς εὑρὼν ἢ καὶ μαθὼν ἔμπροσθεν παρʼ ἑτέρων, ἢ φαῦλα εἶναι τὰ λεχθέντα, ἢ τὸ τρίτον οὐ καθʼ αὑτόν, μείζονα δέ, καὶ ὄντως οὐκ ἂν δυνατὸς εἶναι φρονήσεώς τε καὶ ἀρετῆς ζῆν ἐπιμελούμενος. εἰ μὲν γὰρ φαῦλα, πολλοῖς μάρτυσι μαχεῖται τὰ ἐναντία λέγουσιν, οἳ περὶ τῶν τοιούτων πάμπολυ Διονυσίου κυριώτεροι ἂν εἶεν κριταί· εἰ δὲ ηὑρηκέναι ἢ μεμαθηκέναι, ἄξια δʼ οὖν εἶναι πρὸς παιδείαν ψυχῆς ἐλευθέρας,

that he possesses knowledge, and is his knowledge adequate, as a result of hearing me once only, or as the result of his own researches, or of previous instruction from other teachers? Or does he regard my doctrines as worthless? Or, thirdly, does he believe them to be beyond and above his capacity, and that he himself would be really incapable of living a life devoted to wisdom and virtue? For if he deems them worthless he will be in conflict with many witnesses who maintain the opposite, men who should be vastly more competent judges of such matters than Dionysius. While if he claims that he has found out these truths by research or by instruction, and if he admits their value