WASHINGTON - "The worldly philosophers" was economist Robert Heilbroner's term for such great economic thinkers as Adam Smith, Karl Marx, John Maynard Keynes and Joseph Schumpeter. Today's free-market economists, by contrast, aren't merely not philosophers. They're not even worldly.

Has any group of professionals ever been so spectacularly wrong? Pre-Copernican astronomers and cosmologists, I suppose, and for the same reason really: They had an entire, internally consistent, theoretically rich system that described the universe.

So it is with today's mainstream economists. Theirs is an elegant system, a thing of beauty in itself, as The New York Times' Paul Krugman has argued. It just fails to jell with reality. And unlike the pre-Copernican astronomers, whose dogma posed a threat to those who challenged it but not, at least directly, to anyone else, their latter-day equivalents in the economic profession pose a clear and present danger to the well-being of damned near everyone.

The problem with contemporary economics, at least with the purer strain of free-market economics associated with the University of Chicago, is not simply that it failed to predict the near-collapse of the world financial system last year. The problem is that it believed such a collapse could not happen, that all risk could be quantified by mathematical models and that these quantifications could help us correctly price just about everything. Out of this belief arose the banks' practice of securitization, which put a value on all manner of mortgages and enabled buyers to purchase and swap them with the certainty that such transactions reflected an accurate judgment of the value of the properties and the risks associated with them.

Except, they didn't. So long as economists insisted that they did, however, there really was no need to study such things as bubbles, which only a handful of skeptics and hopelessly retro Keynesians even considered possible. Under mainstream economic theory, which held that everything was correctly priced, bubbles simply couldn't exist.

The one economist who has emerged from the current troubles with his reputation not only intact but enhanced is, of course, Keynes. Every major nation, no matter its economic or political system, has followed Keynes' prescription for combating a major downturn: increasing public spending to fill the gap created by the decline of private spending. That is why the world economy seems to be inching back from collapse and why the nations that have spent the most, China in particular, seem to be recovering fastest.

But Keynes' vision has yet to re-establish itself among economists, who, like the Catholic Church in Galileo's time, aren't about to change their cosmology just because the facts demonstrate that they happen to be wrong. The quants at the banking houses say that they simply failed to sufficiently factor some risks into their mathematical models. Once they do, their system will be corrected, and banks can resume their campaign to securitize everything (as some banks are already doing by establishing a secondary market in life insurance policies).

The problem with that, Robert Skidelsky argues in a new book on economics after the fall, "Keynes: The Return of the Master," is that it neglects one of Keynes' central insights - that an uncertainty attends human affairs that transcends quantifiable risk. (Skidelsky is also the author of a magisterial three-volume biography of Keynes.) Psychology affects value as much as rational calculation does. Thus the state must ensure against periodic madness in the markets with regulations and social insurance, because madness is a potential threat in markets just as it is in other human endeavors - because the market is a human endeavor, not reducible to a mathematical construct.

Will contemporary economists ever accept this last precept? In the 1970s, a wry economist named Robert Lekachman observed that economics students had to master so much mathematics that they became emotionally invested in the idea that the math they had learned explained - had to explain - the universe. Skidelsky calls for combining the postgraduate course in macroeconomics with another discipline - history or psychology, say - to expose young quants to the complexities of human institutions.

If mainstream economics doesn't change, however, it may eventually face the worst of all possible fates: market failure. How many students want to spend their lives quantifying a world that doesn't exist?

Harold Meyerson is editor at large of American Prospect and the L.A. Weekly. This column first appeared in the Washington Post.

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