By Douglas Martin

Published: October 15, 2005

Arthur Seldon, a libertarian economist whose books, pamphlets and articles supplied much of the intellectual artillery that inspired Prime Minister Margaret Thatcher's free-market revolution, died Tuesday at his home in Godden Green in Kent County, England. He was 89.

His death was confirmed by the Institute of Economic Affairs, the research group he helped found and guide.

Long before Mrs. Thatcher came to power in 1979 and attacked many decades of ever-increasing government power through privatization and her other free-market policies, intellectuals on the right were formulating novel approaches to education, health and other government services. So initially radical were their notions that The Independent, a London newspaper, said this week that they were regarded as "political crackpots."

The institute, known by its acronym, I.E.A., "plowed a lonely furrow in its espousal of capitalist ideas," according to Patrick Cosgrave in "Thatcher: The First Term."

Mrs. Thatcher was listening, and regularly lunched at the institute before becoming prime minister, drinking in their message that users, not taxpayers, should pay for government services.

Tony Blair, the current Labor Party prime minister, continued much of Mrs. Thatcher's free-market emphasis. She thanked the "lonely" academics on the 30th anniversary of the institute in 1987, saying, "They were right and they saved Britain."

Mr. Seldon and Ralph Harris, now Lord Harris, the other founder of the I.E.A., steered clear of partisan politics, being careful to portray their thoughts as a product of classical liberal economics. They and their colleagues remained strictly outside of government, unlike many of the conservative research groups whose legions streamed into the administrations of President Reagan and subsequent Republicans. They were not even necessarily members of Mrs. Thatcher's Conservative Party.

Nor were some of their many ideas for transforming the British welfare state, particularly government vouchers to pay for private schooling, ultimately successful. But the institute helped change the nature of Britain's national conservation, as it also oversaw the proliferation of more than 100 similar institutions to nearly 80 countries.

This effort was greatly aided by Mr. Seldon's ability to translate complex economic ideas into clear English. He did this both as an editor of all the institute's publications, more than 350, and as the author of 28 books and some 230 articles.

His trenchant phrasemaking became famous, as in this criticism of socialist economies for providing less choice: "Socialism is a vast machine for churning out piles of goods marked 'Take it or leave it.' "

Critics faulted Mr. Seldon as seeming to start with an ideological answer he liked and then looking around for a question. In a review of Mr. Seldon's 1990 book, "Capitalism," Gordon Brown, a Labor Party leader who is now chancellor of the exchequer, suggested he made a theology out of free markets.

A letter to The Times of London in 1990 attacked Mr. Seldon's contention that the spending decisions of people were truer indications of their wishes than elections. The letter writer pointed out that wealthier people have more votes in such a formulation.

Mr. Seldon countered such criticisms by advocating a negative income tax, under which the poor would be paid money by the government. He said they could then vote with their money for the services they wanted most.

Arthur Seldon was born in the East End of London on May 29, 1916. His parents died in the flu epidemic of 1918. He was adopted by a childless cobbler and his wife, who, like his parents, were Russian-Jewish immigrants.

In 1934, he won a scholarship to the London School of Economics where he studied with Lionel Robbins and Friedrich Hayek, who taught classical liberal economics. Many others in the school embraced socialism or Communism, with which Mr. Seldon briefly flirted.

After graduating with honors, Mr. Seldon worked in a government survey research unit. In 1940, he joined the Army, serving in Africa and Italy. He next taught, edited a trade journal called Store and did research for the beer industry.

At Store, he met and married Marjorie Perrott. He adopted her son from a previous marriage, and they had two more sons. His survivors were not announced.

In 1957, he became editorial director at the institute, which was set up by businessman, Antony Fisher, who had been inspired by a lecture by Mr. Hayek. Lord Harris, as general director, handled finances and recruitment.

Mr. Seldon co-wrote the first pamphlet of the institute, "Pensions in a Free Society." It argued for private pensions, something achieved 30 years later. One of his most widely reviewed books was "Capitalism," which The Economist called "a triumph of the human spirit."

Mr. Seldon liked cricket, opera and having what he called parties for nonconformists at his home, Thatched Cottage, which was quite a large house surrounded by expansive gardens.