Since I began touring with my book The Shock Doctrine, I have had a number of exchanges like this, revolving around the same basic question: when hard-right political leaders and their advisers apply brutal economic shock therapy, do they honestly believe the trickle-down effects will build equitable societies - or are they just deliberately creating the conditions for yet another corporate feeding frenzy? Put bluntly: has the world been transformed over the past three decades by lofty ideology or by lowly greed?

A definitive answer would require reading the minds of men such as Dick Cheney and Paul Bremer, so I tend to dodge. The ideology in question holds that self-interest is the engine that drives society to its greatest heights. Isn't pursuing their own self-interest (and that of their campaign donors) compatible with that philosophy? That's the beauty: they don't have to choose. Unfortunately, this rarely satisfies graduate students looking for deeper meaning. Thankfully, I now have a new escape hatch: quoting Alan Greenspan.

His autobiography, The Age of Turbulence, has been marketed as a mystery solved. The man who bit his tongue for 18 years as head of the Federal Reserve was finally going to tell the world what he believed. And Greenspan has delivered, using his book and the surrounding publicity as a platform for his "libertarian Republican" ideology, chiding George Bush for abandoning the crusade for small government and revealing that he became a policy-maker because he thought he could advance his radical ideology more effectively "as an insider, rather than as a critical pamphleteer" on the margins. Yet the most interesting aspect of Greenspan's story is what it reveals about the ambiguous role of ideas in the free-market crusade. Given that Greenspan is perhaps the world's most powerful living free-market ideologue, it is significant that his commitment to ideology seems rather thin and perfunctory - less zealous belief, more convenient cover story.

Much of the debate around Greenspan's legacy has revolved around the matter of hypocrisy, of a man preaching laissez faire who repeatedly intervened in the market to save the wealthiest players. The economy that is Greenspan's legacy hardly fits the definition of a libertarian market, but looks very much like another phenomenon described in his book: "When a government's leaders routinely seek out private-sector individuals or businesses and, in exchange for political support, bestow favours on them, the society is said to be in the grip of 'crony capitalism'."

He was talking about Indonesia under Suharto, but my mind went straight to Iraq under Halliburton. Greenspan is currently warning the world about a dangerous looming backlash against capitalism. Apparently, this has nothing at all to do with the policies of negligent deregulation that were his trademark. Nothing to do with stagnant wages due to free trade and weakened unions, nor with pensions lost to Enron or the dotcom crash, nor homes seized in the subprime mortgage crisis. According to Greenspan, rampant inequality is caused by lousy high schools (which also have nothing to do with his ideology's war on the public sphere). I debated with Greenspan on the US radio show Democracy Now! recently and was stunned that this man who preaches the doctrine of personal responsibility refuses to take any at all.

Yet ideological contradictions are only relevant if Greenspan really is a true believer. I'm not convinced. Greenspan writes that as a student he had no interest in big ideas. Unlike his classmates in thrall to Keynesianism, with its promise of building a better world, Greenspan was simply good at maths. He started doing research for powerful corporations; it was profitable, but Greenspan made no claims to a higher social contribution. Then he discovered Ayn Rand. "What she did ... was to make me think why capitalism is not only efficient and practical, but also moral," he said in 1974.

Rand's ideas about the "utopia of greed" allowed Greenspan to keep doing what he was doing but infused his corporate service with a powerful new sense of mission: making money wasn't just good for him, it was good for society as a whole. Of course, the flip side of this is the cruel disregard for those left behind. "Undeviating purpose and rationality achieve joy and fulfilment," Greenspan wrote as a zealous new convert. "Parasites who persistently avoid either purpose or reason perish as they should." Was it this mindset that served him well as he supported shock therapy in Russia (72 million impoverished) and east Asia after the 1997 economic crisis (24 million pushed into unemployment)?

Rand has played this role of greed-enabler for countless disciples. According to the New York Times, Atlas Shrugged - Rand's novel that ends with the hero tracing a dollar sign in the air like a benediction - stands as "one of the most influential business books ever written". Since Rand is simply pulped-up Adam Smith, her influence on men such as Greenspan suggests an interesting possibility. Perhaps the true purpose of the entire literature of trickle-down theory is to liberate entrepreneurs to pursue their narrowest advantage while claiming global altruistic motives - not so much an economic philosophy as an elaborate, retroactive rationale.

What Greenspan teaches us is that trickle-down isn't really an ideology after all. It's more like the friend we call after some embarrassing excess who will tell us, "Don't beat yourself up: You deserve it."

· A version of this article appears in the Nation (www.thenation.com)

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