Mr. Izzard shares what’s on his mind: Using false breasts as earmuffs, the unbelievable popularity of balsamic vinegar, Neanderthal man decorating a house …

Not to find a clown sweet and funny is close to heresy, I guess. All clowns are sweet and funny by right. That’s why they’re clowns. They’ve only to appear in white face and do a little mime for us, and voila!—the cynical adult world is magically charmed and returned to purest childhood.

Bill Irwin’s 75-minute The Harlequin Studies at the Signature didn’t do that for me, unfortunately. The "studies" in his title makes his clowning much too dry and academic for my taste. Scholarly, half-jesting references are made to a meeting of Archetype and Individual when all one yearns for is the custard pie. The modest little sketches are textbook stuff: Mischievous Harlequin fools his gullible old master Pantalone once again; Harlequin juggles plate; Harlequin juggles hat; Harlequin walks down invisible stairs; Harlequin falls in love with Wrong Girl. Alas, we see the jokes coming in a dull enchantment zone occupied only by rarefied, overindulged clowning. Everything is in muted good taste. Even when Mr. Irwin is vulgar, he farts quietly.

That said, I must report that the audience as a whole seemed to enjoy Mr. Irwin and his fellow clowns (who tumble a lot). Only a pocket of malcontents surrounding me, as if placed in separate seating for the Anti-Life, failed to respond to his watery reconstruction of traditional commedia dell’arte (cf. commedia, 1550-1800). The vitality and daring of truly spontaneous improvisation—a glorious liberty and individualism that can bring a theater to uncontrolled uproar—are the magical qualities that keep the commedia dell’arte tradition alive. Mr. Irwin, in partnership with the unpredictable extrovert David Shiner, was wonderfully funny in Fool Moon on Broadway. But his lackluster Harlequin Studies needs a red nose, or the child’s infectious, unstoppable howls of laughter.

But what makes me laugh—and what makes you laugh—are mysterious things. Or, as Laurence Olivier once put it charmingly about an admired fellow actor who was playing a comic role, "He’s as much humor as a dead baby in an open coffin." We can theorize about laughter a thousand ways, as Freud and Bergson did, but in the end, why we laugh when we do is an unsolvable mystery. I was once fortunate enough to interview one of the greatest comics in England, Ken (Doddy) Dodd, whose manic, vaudevillian genius was informed by his own very serious studies into the history of laughter. He was an intellectual of humor who once defined Malvolio as the sort of man who used to stand up in a strip club and shout, "What time do the jugglers come on?" He even wondered during our meeting why we make the sound of laughter. "I mean," he suggested in all seriousness, "why doesn’t your nose light up instead?"

There’s no answer to that. But Freud’s theories of comedy were no use to Doddy as a performer. "The problem with Freud," he explained, "is that he never played the Glasgow Empire, second house, Saturday night." The old Glasgow Empire was the fabled graveyard of comics. No fancy Freudian theories could help the entertainer who was brave or foolish enough to go out there and face the mob.

And yet there are people who can make us laugh on sight. Bill Murray makes me laugh without actually doing anything. Jokes per se tend to embarrass me. I always worry I won’t get the joke. Ricky Gervais, the brilliant "anti-comedian" who created the BBC America import The Office, makes me laugh precisely because the character he plays to sly deadpan perfection thinks he’s funny but isn’t. I’ve never found Jerry Seinfeld funny. Steve Martin—always; Chris Rock—no. I prefer Keaton to Chaplin, funnily enough. Anyone who slips on a banana peel is funny. Donald Rumsfeld is funny. So is any Preston Sturges movie, any time. Oscar Wilde isn’t as funny as he would like to be. (He’s witty.) Margaret Cho—no; Jonathan Swift—yes. I threw in Swift to be impressively Swiftian. And all the loved, eccentric performers from my childhood, including this eternal exchange between a drunk and a man nursing a cardboard box under his arm who has just returned from Egypt with an elephant:

"Where do you keep the elephant?" the drunk asks him.

"It’s in this box."

"I thought I heard a rustling!"

Which brings me to my favorite, Eddie Izzard, the transvestite wizard who had us all in stitches during his new Sexie touring show that stopped off at the packed City Center. Times have changed! I first saw him testing the waters hilariously seven years ago at the Performance Space 122 downtown, where he wore high heels, quite modest PVC trousers, green nail varnish, red lipstick, perhaps a dab of rouge. But Uptown Eddie at City Center was wearing knee-high spiked boots, fetching fishnet stockings, a sparkly black skirt slit to the waist, plus a form-fitting bustier, red lipstick (of course), eye makeup that was a little heavy on the kohl, a stylish spiky haircut with great blond highlighting and all of it tastefully set off with diamond earrings.

But this is the point: He’s still our Eddie! Success in America hasn’t spoiled him in the least. He’s always looked like a doll. Why does he dress like a woman? It’s what he likes to do. He’s in artful costume! I wrote when I first saw him that his surprising costume of sexual ambiguity is as traditional and unthreatening as the white-face clown’s. Now here’s a performance that brings an audience to the point of mad laughter while seeming to be utterly, spontaneously improvised. Mr. Izzard doesn’t tell jokes; he isn’t hostile. He doesn’t ask to be liked or loved (but he is). He seems to have no political agenda (though he’s clearly a libertarian). He’s an absurdist storyteller conjuring up insane stage pictures. He’s a literate fantasist in the noble tradition of rambling on about absolutely anything that comes to mind—including using false breasts as earmuffs, the agonizingly slow pace of archaeologists, stabbing children on planes with forks, the unbelievable popularity of balsamic vinegar, the retelling of Homer’s Odyssey from the vantage point of a water skier, dog racing from the point of view of the greyhounds, Neanderthal man decorating a house and—if I heard it right—the sound of cats thrown out of a car window. He’s such a master of the unpredictable that he pretends to get lost. "Where was I?" he asked at one point, peering out at us. "So … yes. But. O.K.! Fifty thousand years ago. Stay with me …." There’s a link, incidentally, with the stream-of-consciousness comedy of one of Britain’s music-hall greats, Frankie Howerd, whose insane diversions and asides gave you the impression that he’d lost the plot, too. "No, don’t. Well. Yes. I mean," Frankie would say. "Pull yourselves together! You’ll make me a laughing stock …. " But there’s no one like Eddie Izzard. I don’t know of any performer who’s as unique or as funny. His comic genius is that his surreal, near-cozy chats liberate us to such dizzying heights that we don’t want to pull ourselves together at all.