For the debut of his latest weighty title, “On War in Philosophy,” the French philosopher Bernard-Henri Lévy made the glossy spreads of French magazines with his trademark panache: crisp, unbuttoned white Charvet shirts, golden tan and a windswept silvery mane of hair.

But this glamorous literary campaign was suddenly marred by an absolute philosophical truth: Mr. Lévy backed up the book’s theories by citing the thought of a fake philosopher. In fact, the sham philosopher has never been a secret, and even has his own Wikipedia entry.

In the uproar that followed over the rigors of his research, Mr. Lévy on Tuesday summed up his situation with one e-mailed sentence: “My source of information is books, not Wikipedia.”

Despite his celebrity as a philosopher, Mr. Lévy has a long history of fending off critics who have attacked his research. In the United States, where Mr. Lévy published “American Vertigo,” his version of traveling in the footsteps of Alexis de Tocqueville, Garrison Keillor wrote a scorching critique in The New York Times Book Review in 2006 citing “the grandiosity of a college sophomore, a student padding out a term paper.”

The blunder particularly resonated in Paris, where Mr. Lévy is a ubiquitous presence on talk shows and in magazines, and is known simply as B.H.L.

In his newest book, Mr. Lévy attacked the 18th-century German philosopher Immanuel Kant as a madman, and in support cited the Paraguayan lectures of Jean-Baptiste Botul to his 20th-century followers.

In fact Mr. Botul is the longtime creature of Frédéric Pagès, a journalist with the satirical weekly Le Canard Enchaîné. “We’ve had a big laugh, obviously,” Mr. Pagès said of Mr. Lévy. “This one was an error that was really simple that the media immediately understood.”...