Aristotle, Rhetoric 1419b
περὶ δὲ τῶν γελοίων, ἐπειδή τινα δοκεῖ χρῆσιν ἔχειν ἐν τοῖς ἀγῶσι, καὶ δεῖν ἔφη Γοργίας τὴν μὲν σπουδὴν διαφθείρειν τῶν ἐναντίων γέλωτι τὸν δὲ γέλωτα σπουδῇ, ὀρθῶς λέγων, εἴρηται πόσα εἴδη γελοίων ἔστιν ἐν τοῖς περὶ ποιητικῆς, ὧν τὸ μὲν ἁρμόττει ἐλευθέρῳ τὸ δ’ οὔ, ὅπως τὸ ἁρμόττον αὑτῷ λήψεται. ἔστι δ’ ἡ εἰρωνεία τῆς βωμολοχίας ἐλευθεριώτερον· ὁ μὲν γὰρ αὑτοῦ ἕνεκα ποιεῖ τὸ γελοῖον, ὁ δὲ βωμολόχος ἑτέρου.
And concerning jokes: since they can be of some use in debates, Gorgias said (and he spoke correctly) that one should destroy the laughter of one’s opponents with seriousness, and their seriousness with laughter. How many kinds of jokes there are has been discussed in my books On Poetics. Among these there are some which are suitable for a gentleman, but others which are unsuitable, so that you should select those which suit you. Irony is more appropriate to a gentleman than ribaldry, as the former causes laughter at one’s own expense, but ribaldry causes laughter at someone else’s expense.