Plato, Gorgias 459b7-c2
Socrates: “So, the politician and the art of rhetoric are also the same regarding the rest of the arts: it isn’t necessary for the speaker to know how the facts themselves stand, but he need only to have found some persuasive device so he seems to those who don’t know anything to know more than those who actually know.”
ΣΩ. Οὐκοῦν καὶ περὶ τὰς ἄλλας ἁπάσας τέχνας ὡσαύτως ἔχει ὁ ῥήτωρ καὶ ἡ ῥητορική· αὐτὰ μὲν τὰ πράγματα οὐδὲν δεῖ αὐτὴν εἰδέναι ὅπως ἔχει, μηχανὴνδέ τινα πειθοῦς ηὑρηκέναι ὥστε φαίνεσθαι τοῖς οὐκ εἰδόσι μᾶλλον εἰδέναι τῶν εἰδότων.
Thanks to @diyclassics for making me read this Greek this morning.