(FORTUNE Magazine) – This year is the 150th anniversary of Karl Marx's The Communist Manifesto, and the effort to rehabilitate the discredited prophet is in full swing. Never mind the dismal track record of Marxism as a governing ideology; article after article proclaims that today's turbulent world economy is just what the great man predicted. One writer in The New Yorker even proclaimed Marx the "thinker of the future."

I say phooey. Sure, Marx wrote about economic upheavals; so did lots of people. What he never managed to do was offer either a comprehensible explanation of why such upheavals happen or any suggestions about what to do about them (except abolish capitalism). By my reckoning, Karl Marx made about as much of a contribution to economics as Zeppo Marx made to comedy. Or as John Maynard Keynes more elegantly put it, "Marxian Socialism must always remain a portent to the historians of Opinion--how a doctrine so illogical and so dull can have exercised so powerful and enduring an influence over the minds of men, and through them, the events of history."

Harsh words, but Keynes earned the right to say them. For it was Keynes, not Marx, who cracked the code of crisis economics and explained how recessions and depressions can happen. As Japan and the rest of Asia have gone into an economic tailspin, it is Keynesianism, not Marxism, that offers useful guidance about how they might save themselves.

I have often wondered why Keynes--unlike, say, Freud--has never become a pop culture icon. His life was certainly interesting enough. Before World War I he was a member of the freethinking bohemian cluster of artists and writers known as the Bloomsbury group. (Trent Lott would not have approved of his private life.) After that war he became famous as the author of The Economic Consequences of the Peace, an eloquent condemnation of the vindictive terms imposed on the defeated Germans; his concern was vindicated by the rise of Adolf Hitler, and the memory of his warnings helped persuade a victorious America to aid, not punish, its enemies after World War II. As that war was drawing to a close, Keynes arrived in New Hampshire as the most important member of the British delegation to the Bretton Woods conference, which established an international monetary system that helped stabilize the world economy for a generation.

But however eventful his resume, only one item on it really matters: his 1936 publication of The General Theory of Employment, Interest, and Money, which was to depression economics what The Origin of Species was to biology. Before the General Theory, economists could not explain how depressions happen or what to do about them. (I've tried going through the pre-Keynesian business-cycle literature; it's a vast wasteland.) After 1936, they could.

True, there was a long, 25-year stretch when many economists turned their backs on Keynes. They claimed, with some justice, that he made assumptions that could not be rigorously justified; purists argued that a theory whose "microfoundations" are based on observation rather than axioms should be regarded as illegitimate, no matter how well it might work in practice. The devaluation of Keynes was helped by the non-Keynesian nature of the problems facing the world in the '70s and '80s--inflation rather than deflation (although in the early '20s it was Keynes who provided the first coherent explanation of the hyperinflations then consuming much of Europe), inadequate saving rather than deficient demand. And for a while various anti-Keynesian ideas--from mathematically impeccable academic demonstrations that recessions can't happen (or if they do, it's because people rationally choose to enjoy more leisure) to popular crank doctrines like supply-side economics--seemed to have crowded Keynes off the stage. But just take a look at Japan--an economy that suffers from a lack of demand, not supply; where the danger is deflation, not inflation--and tell me Keynesian ideas are no longer relevant.

So why isn't Keynes a household name? Perhaps because we want our gurus to look and sound the part. Our saviors are supposed to look like an Old Testament prophet and rage against the evils of the world; a fedora-wearing member of the Establishment, who wants to rescue the system rather than destroy it, can't make it past the casting department, no matter how unconventional his private life or his ideas. Keynes also had an off-putting belief that good economics is the product of hard thinking. "Economics is a difficult and technical subject," he once wrote, "but nobody will believe it." Worst of all, instead of presenting depressions as a morality play, with villains and heroes, he portrayed them as a dangerous but treatable disease in an otherwise healthy patient. Indeed, he once expressed the hope that economists might someday be thought of like dentists--apolitical professionals brought in to resolve technical problems.

Now I'm not saying that Keynes was right about everything. But the essential truth of Keynes' big idea--that an economy can fail if consumers and investors spend too little, that the pursuit of sound money and balanced budgets is sometimes (not always!) folly--is as evident in today's world as it was in the 1930s. And in these dangerous days, we ignore or reject that idea at the world economy's peril.

PAUL KRUGMAN is an economics professor at MIT and author of The Accidental Theorist.