Paul Kurtz, who became a national leader in efforts to debunk paranormal phenomena and pseudoscience — what he called “insidious” gimmicks that had blossomed into an industry profiting on ignorance, died Oct. 20 at his home in Amherst, N.Y. He was 86.

He had a heart arrhythmia, but the immediate cause of death has not been determined, said his son, Jonathan Kurtz.

Dr. Kurtz taught philosophy for 25 years at the State University of New York at Buffalo and drew broader influence through his thousands of media appearances promoting the need for skepticism and rational thinking. He counted among his supporters the astronomer Carl Sagan, authors Isaac Asimov and Martin Gardner, and the behaviorist B.F. Skinner.

Dr. Kurtz, who wrote and edited dozens of books, oversaw a sprawling organization that included the Amherst-based Center for Inquiry, the Committee for Skeptical Inquiry (formerly the Committee for the Scientific Investigation of Claims of the Paranormal) and the publishing house Prometheus Books. He also edited the Humanist, a magazine published by the Washington-based American Humanist Association.

Dr. Kurtz once defined his vision as defending “the philosophy of skepticism — especially as an antidote for public gullibility — and the values of the secular and humanist outlook.”

Paul Kurtz, the secular humanist philosopher, died Oct. 20, at his home in the Buffalo suburb of Amherst, N.Y. His death was announced Oct. 22 by the Center for Inquiry, which he founded. (DON HEUPEL/AP)

His influence and prominence grew with the spread of cultlike religious movements in the 1970s as well as the purported psychic abilities of the spoon-bending media sensation Uri Geller.

“There is always the danger that once irrationality grows, it will spill over into other areas,” he told the New York Times in 1977. “There is no guarantee that a society so infected by unreason will be resistant to even the most virulent programs of dangerous ideological sects.”

Dr. Kurtz was disturbed by a growing tendency of news media outlets to give what he considered uncritical coverage of psychics, fortunetellers, astrologers, and sightings of UFOs and Bigfoot.

After the release of the Steven Spielberg film “Close Encounters of the Third Kind” (1977), Dr. Kurtz braced for a new round of claims regarding abductions by aliens and cattle mutilations by supernatural forces.

Speaking to The Washington Post in 1978, he warned of “a reversion to primitive credulity in the world’s most technologically advanced country.”

He assailed Erich von Daniken, the author of “Chariots of the Gods” and other books that fascinated millions of readers by asserting that extraterrestrial beings left behind signs of their presence in Mayan temples, the Easter Island moai and other structural wonders.

Dr. Kurtz’s Committee for the Scientific Investigation of Claims of the Paranormal filed complaints with the Federal Communications Commission and two congressional subcommittees against NBC for broadcasting “Exploring the Unknown,” a 1977 program narrated by actor Burt Lancaster that used a documentary-like approach to topics such as “psychic surgery” by Filipino faith healers claiming to remove a tumor by making incisions with psychic forces.

Dr. Kurtz was bluntly dismissive of the growth in alternative medicine.

“Homeopathy, magnetic therapy, therapeutic touch and acupuncture, growing every year, are complete nonsense and have only proven to have had a placebo effect,” he told Forbes magazine in 2000, “yet some of these subjects are being taught in medical schools.”

Paul Winter Kurtz was born Dec. 21, 1925, in Newark. He described his parents, a businessman and a homemaker, as “freethinkers.”

During World War II, he served in the Army in Europe and participated in the Battle of the Bulge. He was in a unit that saw Dachau and Buchenwald concentration camps soon after their liberation.

After the war, he studied at New York University under philosopher Sidney Hook, whose pragmatist beliefs profoundly influenced him. He graduated in 1948 and earned a doctorate in philosophy from Columbia University in 1952. He taught at several colleges before joining the State University of New York at Buffalo, where he worked from 1965 to 1991.

In 1969, he created Prometheus Books, a publishing house that released titles by authors including Gardner (“Science: Good, Bad and Bogus”) and Asimov. The Committee for the Scientific Investigation of Claims of the Paranormal, which began in the mid-1970s, published the Skeptical Inquirer to combat pseudoscience. Another of his magazines, Free Inquiry, campaigned against horoscopes in newspapers.

In 2010, Dr. Kurtz resigned from the Center for Inquiry’s board of directors, saying he disapproved of some of its recent projects, such as International Blasphemy Rights Day, as “angry atheism.” He then founded another group, the Institute for Science and Human Values.

He coined the term “eupraxophy” to describe an ethical, joyful lifestyle based on logic and reason rather than transcendental beliefs. The word, based on the Greek roots for “good,” “practice” and “wisdom,” was the title of one of his books, “Eupraxophy: Living Without Religion” (1989).

Survivors include his wife, Claudine Vial Kurtz; four children; a brother; a sister; and five grandchildren.

In 1987, Dr. Kurtz was asked by the Chicago Tribune what he would do if he ever encountered God.

“I’d immediately pass out pamphlets, asking God to change the furniture in the universe and reorder it in a more just way,” he said, before adding: “This is hypothetical, of course.”