Mr. Dennett, the co-director of the Center for Cognitive Studies at Tufts University and perhaps America’s most widely read (and debated) living philosopher, recently sold the Xanthippe, his 42-foot cruiser, named for Socrates’ reputedly shrewish wife. But he still had his boat shoes, his Darwin-esque beard, and an eagerness to demonstrate his sail-handling skills while discussing his 16th book, “Intuition Pumps and Other Tools for Thinking,” which W. W. Norton is publishing next week.

Never mind that the boathouse’s fleet was unexpectedly confined to shore, thanks to a temporary shutdown of river traffic. And never mind that the boats lacked a boom crutch, the piece of nautical equipment that Mr. Dennett uses in the book as a punning name for the kind of faulty thinking tool that blows up in (mostly other) philosophers’ faces.

Sailing was still an apt illustration of the kind of empirically minded problem-solving that Mr. Dennett has long preferred to the abstractions of more traditional philosophy, to the great irritation of some colleagues.

“Philosophers can seldom put their knowledge to practical use,” Mr. Dennett said, squinting under the brim of a baseball hat reading “Freedom Evolves,” a play on the title of his 2003 book on free will. “But if you’re a sailor, you can. I just get a kick out of that.”

These days, Mr. Dennett, 71, is most famous for his blunt-talking atheist activism. “There’s simply no polite way to tell people they’ve dedicated their lives to an illusion,” he said flatly.

But for decades, he has presented himself among his fellow philosophers as a ruthless slayer of metaphysical fancy.

“It’s always good fun to argue with him,” said David Chalmers, a professor of philosophy at New York University and Australian National University, who has long crossed swords with him over the nature of consciousness. “In person, he’s very charming, teasing and joking, though sometimes he’s less good-tempered in print.”

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