There are, of course, those who are so innocent of improper impulses as to be beyond the reach of lewd humor. A while back, shortly after Bill Clinton went on a successful diet, someone cracked, "Clinton's lost so much weight, now he can see his intern." This struck me as a pretty good joke, so I repeated it to several of my rock-ribbed Republican friends, thinking that they would enjoy a little mockery of the former president. But the joke left them nonplused. "I don't get it," was the universal reaction. To the pure, all things are pure.
And to those of you who find the Clinton joke offensive: Honi soit qui mal y pense (the motto of the Order of the Garter -- which here might be rendered "Shame on you if you know enough to take offense.")
Sexual humor does not so much corrupt us as remind us that we are already corrupted. Only in modern times has it been feared. The sole surviving joke book we have from the Greek and Roman world, the Philogelos, or "Laughter-Lover," abounds with sex jokes. Probably put together in the 4th or 5th century, the volume contains 264 numbered jokes, the most haunting of which is surely No. 114, about a resident of Abdera, a Greek town whose citizens were renowned for their foolishness. "Seeing a eunuch, an Abderite asked him how many children he had. The eunuch replied that he had none, because he lacked the means of reproduction. Retorted the Abderite... " The rest is missing from the surviving text, which goes to show the strange potency of unheard punch lines.
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The other time-honored view of humor has a rather sweeter flavor, and a more intellectual one. It is the "incongruity theory," versions of which were held by Blaise Pascal, Immanuel Kant and Arthur Schopenhauer, which says that we laugh when the decorous suddenly dissolves into the absurd. "Do you believe in clubs for small children?" W.C. Fields was once asked. "Only when kindness fails," he replied.
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But take this joke, reputedly a favorite of George H.W. Bush: "How do you titillate an ocelot? You oscillate its tits a lot." Ostensibly, it falls into the category of raunch, with its use of the not-ready-for-prime-time word for breasts and its winking allusion to bestiality. But it is essentially sheer nonsense, a sonic jeu d'esprit. (Compare: "I'd rather have a bottle in front of me than a frontal lobotomy.")
Such "innocent" jokes, as Freud called them, serve to overcome the adult inhibition against play. Even the primmest of dowagers will emit a reluctant chuckle.
What makes sexual humor funny is precisely the sort of playful incongruity that redeems it from pure lewdness. The dirty joke has been evolving over the centuries, and I like to think that this is a story of progress, with nastiness and filth giving way to the intellectual delight in the absurd.