Francis Wheen is a journalist and author of several books, including a highly acclaimed biography of Karl Marx. His collected journalism, Hoo-Hahs and Passing Frenzies, won the George Orwell prize in 2003.

Francis Wheen's new book, How Mumbo-Jumbo Conquered the World: A Short History of Modern Delusions, is published by Fourth Estate.

1. "God is on our side"

George W Bush thinks so, as do Tony Blair and Osama bin Laden and an alarmingly high percentage of other important figures in today's world. After September 11 2001 Blair claimed that religion was the solution not the problem, since "Jews, Muslims and Christians are all children of Abraham" - unaware that the example of Abraham was also cited by Mohammed Atta, hijacker of the one of the planes that shattered the New York skyline. RH Tawney wrote in Religion and the Rise of Capitalism that "modern social theory, like modern political theory, developed only when society was given a naturalistic instead of a religious explanation". In which case modern social and political theory would now seem to be dead.

2. The market is rational

Financial sophisticates in the 21st century smile at the madness of the South Sea Bubble or the absurdity of the Dutch tulip craze. Yet only a few years ago they scrambled and jostled to buy shares in dotcom companies which had no earnings at all nor any prospect of ever turning a profit. To justify this apparent insanity, they maintained that such a revolutionary business as the internet required a new business model in which balance sheets were irrelevant. In short, they thought they had repealed the laws of financial gravity - until they came crashing down to earth.

3. There is no such thing as reality

Hence the inverted commas which postmodernists invariably place round the word. They see everything from history to quantum physics as a text, subject to the "infinite play of signification". But if all notions of truth and falsity cease to have any validity, how can one combat bogus ideas - or indeed outright lies? There is, for instance, a mass of carefully empirical research on the Nazi extermination of the Jews. As Professor Richard Evans points out, "To regard it as fictional, unreal or no nearer to historical reality than, say, the work of the 'revisionists' who deny that Auschwitz ever happened at all, is simply wrong. Here is an issue where evidence really counts, and can be used to establish the essential facts. Auschwitz was not a discourse."

4. We mustn't be "judgmental"

In 2002 the Guardian revealed that Christian fundamentalists had taken control of a state-funded school in Gateshead and were striving to "show the superiority" of creationist beliefs in their classes. When Jenny Tonge MP asked Tony Blair if he was happy that the Book of Genesis was now being promoted as the most reliable biology textbook, he replied: "Yes. . . In the end a more diverse school system will deliver better results for our children." This is the enfeebling consequence of unthinking cultural and intellectual relativism. If some schools start teaching that the moon is made of Swiss cheese or that the stars are God's daisy chain, no doubt that too will be officially welcomed as a healthy sign of educational diversity.

5. Laissez-faire capitalism is the prerequisite for trade and prosperity

The International Monetary Fund may say so, as it imposes Thatcher-style solutions all over the world, but its own figures tell a different story. Its report on The World Economy in the 20th Century", published in 2000, includes a graph - printed very small, perhaps in the hope that no one would notice - which shows that the pre-Thatcherite period between 1950 and 1973 was by far the most successful of the century. This was an era characterised by capital controls, fixed exchange rates, strong trade unions, a large public sector and a general acceptance of government's role in demand management. The average annual growth in "per capita real GDP" throughout the world was 2.9% - precisely twice as high as the average rate in the two decades since then.

6. Astrology and similar delusions are "harmless fun"

Those who say this never explain what is either funny or harmless in promoting a con-trick which preys on ignorance and anxiety. Yet even the Observer, Britain's most venerable and enlightened Sunday newspaper, now has a horoscope page.

7. Thin air is solid

Charles Leadbeater's book Living on Thin Air (1999), a starry-eyed guide to the "weightless economy", was described by Peter Mandelson as "a blueprint for what a radical modernising project will entail in years to come". The dustjacket also carried a tribute from Tony Blair, hailing Leadbeater as "an extraordinarily interesting thinker" whose book "raises criticial questions for Britain's future". Three years later, after the pricking of the dotcom bubble, industry secretary Patricia Hewitt admitted that "industrial policy in [Labour's] first term of office was mistaken, placing too much emphasis on the dotcom economy at the expense of Britain's manufacturing base...The idea of Living on Thin Air was so much hot air." Tactfully, she forgot to mention that the chief hot-air salesman had been her own leader.

8. Sentimental hysteria is a sign of emotional maturity

The psychotherapist Susie Orbach interpreted the 'floral revolution' outside Kensington Palace after Princess Diana's death as proof that we were "growing up as a nation". Will Hutton, radical social democrat and republican, said that the collective genuflection before a dead aristocrat showed that the British were "freeing ourselves from the reins of the past". The assumption is that emotional populism represents a new kind of collective politics. In fact, it is nothing more than narcissism in disguise.

9. America's economic success is entirely due to private enterprise

In the 19th century, the American government promoted the formation of a national economy, the building of railroads and the development of the telegraph. More recently, the internet was created by the Pentagon. American agriculture is heavily subsidised and protected, as are the steel industry and many other sectors of the world's biggest "free-market economy". At times of economic slowdown, even under presidents who denigrate the role of government, the US will increase its deficit to finance expansionary fiscal and monetary policies. But its leaders get very cross indeed if any developing country tries to follow this example.

10. "It could be you. . ."

This was the advertising slogan for the National Lottery, that monument to imbecility, which was introduced (fittingly enough) by John Major. And millions of British adults apparently believed it, even though the odds on winning the jackpot are 13m to one. It could be you. . . but it bloody well won't be.