Plato, Letters 341c

καὶ γραψόντων, ὅσοι φασὶν εἰδέναι περὶ ὧν ἐγὼ σπουδάζω, εἴτʼ ἐμοῦ ἀκηκοότες εἴτʼ ἄλλων εἴθʼ ὡς εὑρόντες αὐτοί· τούτους οὐκ ἔστιν κατά γε τὴν ἐμὴν δόξαν περὶ τοῦ πράγματος ἐπαΐειν οὐδέν. οὔκουν ἐμόν γε περὶ αὐτῶν ἔστιν σύγγραμμα οὐδὲ μήποτε γένηται· ῥητὸν γὰρ οὐδαμῶς ἐστιν ὡς ἄλλα μαθήματα, ἀλλʼ ἐκ πολλῆς συνουσίας γιγνομένης περὶ τὸ πρᾶγμα αὐτὸ καὶ τοῦ συζῆν ἐξαίφνης, οἷον ἀπὸ πυρὸς

concerning all these writers, or prospective writers, who claim to know the subjects which I seriously study, whether as hearers of mine or of other teachers, or from their own discoveries; it is impossible, in my judgement at least, that these men should understand anything about this subject. There does not exist, nor will there ever exist, any treatise of mine dealing therewith. For it does not at all admit of verbal expression like other studies, but, as a result of continued application to the subject itself and communion therewith, it is brought to birth in the soul on a sudden, as light that is kindled