His death was confirmed by his stepdaughter Elizabeth Glazer.

Mr. Gay, a refugee from Nazi Germany, devoted his career to exploring the social history of ideas, a quest that took him far from his original area of specialization, Voltaire and the Enlightenment. “He is one of the major American historians of European thought, period,” said Sander L. Gilman, a cultural and literary historian at Emory University.

It was his work on the 18th century that sealed Mr. Gay’s reputation as one of the pre-eminent historians of his generation. “Voltaire’s Politics,” published in 1959, was followed by “The Enlightenment: An Interpretation,” a monumental two-part study whose first volume, subtitled “The Rise of Modern Paganism,” won the National Book Award in 1967. The second volume, subtitled “The Science of Freedom,” was published in 1969.

“That is the last great work to provide a synthetic account of the philosophes and their world,” said Margaret Jacob, a professor of history at U.C.L.A. “It was canonical. He just had an encyclopedic grasp of the subject.”

A longstanding interest in Freud’s ideas led Mr. Gay to train at the Western New England Institute for Psychoanalysis and motivated him to write a revisionist psychohistory of the Victorian middle classes, “The Bourgeois Experience: Victoria to Freud,” whose five volumes were published in the 1980s. He also wrote the acclaimed “Sigmund Freud: A Life for Our Time” (1988), the first substantial Freud biography since Ernest Jones’s three-volume one in the 1950s.

Freud and Mr. Gay were both assimilated, nonreligious Jews nourished by and trapped in a Germanic culture whose anti-Semitic undercurrents gathered strength around them. Their shared predicament provoked some of Mr. Gay’s most personal and anguished historical writing, notably the essays in “Freud, Jews and Other Germans” (1978) and the autobiographical “My German Question: Growing Up in Nazi Berlin” (1998).

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