Harvard sociologist Nathan Glazer in 1969. (JHU Sheridan Libraries/Gado/Getty Images)

Nathan Glazer, an urban sociologist and scholar of ethnicity, race and education whose intellectual odyssey took him from the socialist left to the neoconservative right to a label-defying position near the political center, died Jan. 19 at his home in Cambridge, Mass. He was 95.

His daughter Sarah Glazer Khedouri confirmed the death but did not give a precise cause.

A self-described “mild radical” in the 1950s, Dr. Glazer was part of a group of left-leaning thinkers who were “mugged by reality,” in journalist Irving Kristol’s formulation, and turned against the social programs of President Lyndon B. Johnson’s Great Society initiative in the 1960s.

That group became known as the neoconservatives, a term that originated as a pejorative under socialist political theorist Michael Harrington before being embraced by Kristol and rejected by Dr. Glazer, who ultimately considered himself a centrist Democrat, according to friends. He told the Wall Street Journal last year that he voted Republican only once, in Massachusetts, to protest “the fact that some Kennedy was being elected from the district again and again.”

Dr. Glazer worked in the John F. Kennedy administration, in what is now the Department of Housing and Urban Development, and was a consultant to Johnson’s Model Cities program. But he drew on social science research to conclude that programs designed to alleviate poverty — including Head Start, the Job Corps and Meals on Wheels — were counterproductive.

States that emphasized such programs did not always see results, he found, particularly in the realm of education. In Dr. Glazer’s view, those initiatives discouraged self-sufficiency and were incapable of addressing the real issue: a deterioration of the family and other social units fundamental to American life.

“Whereas the prevailing wisdom was that social policies would make steady progress, I came to believe that although social policy had ameliorated some of the problems we had inherited, it had also given rise to other problems no less grave in their effect on human happiness,” he wrote in “The Limits of Social Policy” (1988).

Dr. Glazer was one of the last surviving members of the New York Intellectuals, a group of sharp-elbowed writers and critics who helped drive the country’s intellectual discourse in the middle of the 20th century, writing articles in the pages of small magazines such as Commentary, Partisan Review and eventually the Public Interest.

Founded in 1965 by Kristol and sociologist Daniel Bell, the Public Interest became a bastion of neoconservative thought, even as Dr. Glazer tried to preserve it as a space for rigorous public policy analysis while serving as co-editor from 1973 to 2002.

“He was the most inductive thinker I ever knew, and the most curious,” said Mark Lilla , an intellectual historian at Columbia University who edited a book with Dr. Glazer and worked with him at the Public Interest. “He was interested in looking at the evidence, rather than looking for evidence that supported whatever hypothesis he had, and was always on the lookout for evidence that he was wrong.”

Indeed, Dr. Glazer’s intellectual reputation was primarily that of a perennial reassessor. A New York Times profile in 1998, headlined “Nathan Glazer Changes His Mind, Again,” began: “Nathan Glazer has had more second thoughts in his lifetime than most people have had thoughts.”

A longtime professor at Harvard University, Dr. Glazer was a co-author of two seminal works of social science. The first, “The Lonely Crowd” (1950), is sometimes cited as the most popular work of American sociology.

Primarily written by David Riesman, with contributions from Reuel Denney and Dr. Glazer, the book proposed three character types with which to divide society — “other-directed,” “inner-directed” and “tradition-directed” — and was widely seen as a swipe at American consumerism and conformity.

His other signature work, “Beyond the Melting Pot” (1963), was one of the first serious studies of ethnicity and assimilation. Written with Daniel Patrick Moynihan, the scholar turned U.S. senator, the book examined black, Puerto Rican, Jewish, Italian and Irish populations in New York City. America, the writers found, was less a melting pot than a mosaic, in which the identities of different racial and ethnic groups persisted generations after their arrival in the United States.

Somewhat controversially, Dr. Glazer also argued that prejudice and racism alone could not explain the “concentration of problems in the Negro community.” Values and behavior also played a significant role, in his view, although he believed that civil rights legislation passed in the mid-1960s would effectively enable African Americans to rise up the social and economic ladder.

When that advancement never came to pass, his views began to shift, perhaps most notably in the field of affirmative action. While his 1975 book “Affirmative Discrimination” argued that “public policy must be exercised without distinction of race, color or national origin,” he later championed a pragmatic approach to higher education admissions, one that employed a racial preference.

While conservatives lambasted him, suggesting he had sold out in the face of pressure from liberal colleagues, Dr. Glazer insisted he was once again changing his views only in the face of shifting evidence. He had never abandoned his ideals, he said, only adjusted his thinking on how best to achieve them.

“[When] I look at policies that are trying to improve welfare,” he said in the 1997 documentary “Arguing the World,” according to the magazine City Journal, “I think you must keep on trying even if you have not had great success.”

The youngest of seven children, Nathan Glazer was born in Manhattan on Feb. 25, 1923. Both parents were Jewish immigrants from Poland; his father was a sewing-machine operator, and his mother was a homemaker. A brother, Joe Glazer, became a protest singer known as “labor’s troubadour” for his performances at picket lines and union rallies.

Dr. Glazer studied sociology at the City College of New York, where, according to “Arguing the World,” he argued, ate lunch and played table tennis in a cafeteria alcove with Bell, Kristol and literary critic Irving Howe. “One of the characteristics of [our] group was a notion of its universal competence,” he said, adding that he and his friends “shot our mouths off on” everything from culture to politics. Their approach, he added, stemmed from “the arrogance that if you’re a Marxist, you can understand anything, and it was a model that even as we gave up our Marxism we nevertheless stuck with.”

He received a bachelor’s degree in 1944, earned a master’s degree in linguistics from the University of Pennsylvania that same year, and went on to work as an editor at Commentary, Anchor Books and Random House. Dr. Glazer received his doctorate in sociology from Columbia University in 1962 and taught at the University of California at Berkeley, Bennington College in Vermont and Smith College in Northampton, Mass., before joining Harvard in 1969.

His first marriage, to writer Ruth Slotkin, ended in divorce. Survivors include his wife of 57 years, the former Sulochana Raghavan of Cambridge; three daughters from his first marriage, Sophie Glazer of Stuart, Fla., and Elizabeth Glazer and Glazer Khedouri, both of Manhattan; seven grandchildren; and two great-grandchildren.

Dr. Glazer sometimes traced the pivotal moment in his intellectual evolution — his “mugged by reality” moment, as it were — to the 1960s, when he became disillusioned with the student Free Speech Movement while teaching at Berkeley. But that was just the beginning of a career spent grappling with the chief tenets of the left and the right.

“You begin to break with orthodoxy, and then you see other challenges to it,” he told the New York Times in 1998. “They don’t seem so outlandish or threatening as they once did.”

“It reminds me of the old Leninist line,” he added: “ ‘Who says A, must say B.’ From saying B, you’ll go on to C, D and you’ll end up at Z. There’s no stopping.”