FORTUNE -- Life's pretty good these days for French economist Thomas Piketty, who spent Wednesday evening having his book, Capital in the Twenty-First Century, lavishly praised by two of the world's most famous economists -- Paul Krugman and Joseph Stiglitz -- who just happen to own three Nobel Prizes between them.
Piketty would probably prefer that the book that is garnering him such attention were the bearer of better news. But economists don't tend to gain renown by assuring the public that everything is A-Okay. That is certainly not the message of Capital, a 600-plus page work that convincingly warns readers that rising global wealth and income inequality over the past generation is actually the norm for capitalist economies, and that we should expect that trend to continue in the years to come.
The title of the book is an allusion to Karl Marx's famous critique of capitalism, and Piketty's analysis shows that Marx was right to believe that wealth concentration would inexorably increase in capitalist societies. Piketty draws upon work he and colleagues like Anthony Atkinson of Oxford and Emmanuel Saez of Berkeley have done in recent years to show that income and wealth inequality are increasing in the rich world, and to argue that the more egalitarian economic distribution seen after World War II was an anomaly that we can't expect to return to unless we implement government policies to bring it about.
A debate on Wednesday evening at CUNY's The Graduate Center featuring Piketty, Krugman, Stiglitz, and University of Wisconsin economist Steven Durlauf helped distill some of the ideas presented in Capital, and to critique its weaker points.
Piketty's colleagues were quick to praise the book. Krugman lauded it as a "unified field theory" of economics which joins together the study of economic growth, the distribution of income between capital and labor, and income inequality. Stiglitz was equally taken by the work, arguing that Americans would not be bothered by increased inequality if it were based on merit within a society that enables class mobility. But the U.S. is near the bottom when it comes to social mobility.
Durlauf played the role of the critic in the debate, poking holes in some of the more technical aspects of Piketty's argument, like his dismissal of the "marginal product theory" of wages (which basically asserts that a worker is paid based on his marginal contribution to a commercial enterprise) without suggesting some theory to replace it. He also suggested that Piketty should spend more time thinking about whether technology could be the reason, rather than capitalism itself, for growing disparities in wealth and income.
This critique, like those that have been offered by conservative economists Greg Mankiw and Kevin Hassett, doesn't do anything to challenge the evidence that pre-tax income and wealth inequality is growing very quickly in the rich world. Mankiw, for instance, has argued that things like government subsidies, social security, and welfare have increased people's after-tax income, so Piketty's evidence of rising inequality shouldn't be taken seriously. But such programs just show that the government is already responding to increased inequality by redistributing wealth.
The most interesting argument against Piketty's idea that a global wealth tax is needed to combat inequality comes from Kevin Hassett of the American Enterprise Institute. He points out that the rise in inequality in the wealthy world over the past generation has been matched by similarly striking reductions in global inequality, and if we are studying this issue on a global scale, this reduction in inequality makes the need for a global wealth tax seem unnecessary. Hassett also believes it's important for those of us in the developed world to not take a self-centered view of global capitalism, and that we should be hesitant to mess with a system that has brought so many people out of poverty over the past 30 years.
But none of Piketty's critics have been able to disprove the rise in pre-tax wealth and income inequality on a national level. Capital, in other words, has shifted the debate from the question of whether inequality is a problem to what exactly we should do about it.
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