Philip E. Slater, a prominent sociologist and lodestar of the countercultural movement who abandoned academia to escape the hollow existence he decried in his best-selling volume “The Pursuit of Loneliness,” died June 20 at his home in Santa Cruz, Calif. He was 86.

The cause was lymphoma, said his wife, Susan Helgeson.

By his early 40s, Dr. Slater had achieved what many Americans would have then and would still today consider markers of considerable success: a Harvard education, chairmanship of the sociology department at Brandeis University and publication of a book that would sell half a million copies.

In that book — “The Pursuit of Loneliness: American Culture at the Breaking Point” (1970) — Dr. Slater examined the cherished American value of individualism. He argued that it was not an absolute virtue, but rather the cause of the emptiness afflicting so many in his generation. He essentially argued that, as Americans strove harder for achievements, they pulled farther away from community and the fulfillment it offered.

“We all have our quirks, which provide surface variety,” he wrote, “but aside from this, human beings have very little basis for their persistent claim that they are not all members of the same species.”

Philip E. Slater (Susan Helgeson)

Kenneth Keniston, then a Yale University psychology professor, wrote in the New York Times that the book was a “brilliant, sweeping and ‘relevant’ critique of modern America.” As readers swarmed to the volume, apparently seeking an alternative to societal careerism and competition, Dr. Slater took a place among the leading sociologists and social critics of the day.

But academic life “disappointed” him, he would later tell a Harvard publication. Shortly after publication of his book, he left Brandeis and helped co-found Greenhouse, a personal growth center in Cambridge, Mass. His colleagues in that endeavor included Morrie Schwartz, the late Brandeis professor featured in Mitch Albom’s popular book “Tuesdays With Morrie.”

By the mid-1970s, Dr. Slater settled in California, took up acting and pursued playwriting. In 1980, he published another noted book, “Wealth Addiction,” in which he decried American materialism and promoted the “voluntary simplicity” that he had implemented in his own life. At the time of his death, one of his children told the Santa Cruz Sentinel that he owned enough worldly possessions to fill two small totes.

Dr. Slater acknowledged that his lifestyle brought with it financial hardship, but he insisted that the advantages far outweighed the difficulties.

“It was the experience of losing everything and finding I was having a wonderful time,” Dr. Slater once told an interviewer. “When I lost control over my life, it opened me to experiences I otherwise would not have had. I would have protected myself against them. . . . I hadn’t lost anything precious.”

“The Pursuit of Loneliness” was republished in 1976 and in 1990 — a measure, perhaps, of its abiding relevance.

Philip Elliot Slater was born May 15, 1927, in Riverton, N.J. His father was a shipping and railroad executive. During World War II, the younger Slater served in the U.S. Merchant Marine.

He received a bachelor’s degree in government in 1950 and a doctorate in 1955, both from Harvard. While at the university, he was among the students who participated in scientific testing of the hallucinogenic drug LSD.

“It definitely felt like we were expanding our consciousness,” he was quoted as saying in Don Lattin’s book “The Harvard Psychedelic Club.” “From that moment, we saw the world differently than people who had not had the experience.”

Throughout his career, Dr. Slater was deeply interested in issues surrounding democracy.

In “The Temporary Society” (1968), coauthored with leadership consultant Warren Bennis, he predicted that democracy would win out over other forms of government during the Cold War. In “A Dream Deferred” (1991), Dr. Slater examined the ways democratic ideals had been neglected in the United States.

“Everyone talks about democracy,” he wrote, “but few people have any idea why it exists, why it is happening now, or where it will lead. Most people see it as a merely political phenomenon — which is a little like seeing TV as merely an electrical phenomenon.”

Dr. Slater’s creative output included “How I Saved the World,” a 1985 novel centering on Taylor Bishop, a onetime mental patient who takes upon himself the burden of averting nuclear war. Writing in The Washington Post, reviewer Wray Herbert described it as a “preposterous but thoroughly engaging” story.

Dr. Slater’s marriages to Gwen MacEllven, Jeanne Durling and Dori Appel ended in divorce. Survivors include his wife of 22 years, Susan Helgeson of Santa Cruz; three children from his first marriage, Wendy Palmer of Oak Bluffs, Mass., Scott Slater of Cambridge, Mass., and Stephanie Slater of Watertown, Mass.; a daughter from his third marriage, Dashka Slater of Oakland, Calif.; two stepdaughters, Christie Castro of Atascadero, Calif., and Melanie Beck of Aptos, Calif.; eight grandchildren; and two great-grandchildren.

For “Wealth Addiction,” Dr. Slater chose a fitting and poignant epigraph attributed to Yoshida Kenko, the 14th-century philosopher: “Since olden times, there has rarely been a sage who was wealthy.”