Oratory is good only if it has the qualities of fitness for the occasion, propriety of style, and originality of treatment, while in the case of letters there is no such need whatsoever.
τοὺς μὲν γὰρ λόγους οὐχ οἷόν τε καλῶς ἔχειν, ἢν μὴ τῶν καιρῶν καὶ τοῦ πρέποντος καὶ τοῦ καινῶς μετάσχωσιν, τοῖς δὲ γράμμασιν οὐδενὸς τούτων προσεδέησεν.
Original text (Ancient Greek)