Then, just after the start of the Iraq war, “There was a miniburst of optimism” that capitalism was leading to democracy after all, Mr. Mandelbaum said, with three popular uprisings in Ukraine, Georgia and Kyrgyzstan and elections in Gaza, Lebanon and Egypt in 2005. The burst quickly fizzled though, when the democratic “revolutions” proved short-lived and prone to violence and corruption. Now some scholars argue that a free market can even end up undermining democracy. “Capitalism doesn’t necessarily lead toward democracy at all,” Mr. Scott said. “The one thing that you can say is that capitalism is going to relentlessly produce inequality of income, and eventually that is going to become incompatible with democracy.” That is where political leadership and institutions come in.

Another problem, said Lord Dahrendorf, a research professor at the Social Science Research Center Berlin, is that when democracy fails to deliver the economic goods, people begin to doubt its value. “Few things seem more difficult and yet few things are more important for sustainable liberty,” he wrote recently, “than to separate capitalism and democracy in people’s minds.” Otherwise, instead of mutually reinforcing each other, the two spiral into disenchantment.

Even if capitalism does not assure democracy’s existence, many economists and political scientists say it creates a hospitable atmosphere and helps democratic systems withstand turmoil. Nor should we forget, Mr. Stiglitz counsels, that “the movement from closed to open society is a very big change.” To compete economically, a nation has to be plugged into the global information network, which exposes its citizens to other political systems and cultures. Reinforcing that trend, Mr. Mandelbaum said, is that the “habits and values of a market economy, when transferred to the political sphere, make for a democracy.”

But China, he acknowledges, is “the big enchilada, the big test.” Even with its growing middle class, it still has a billion poor people. Pressure for democracy will increase, but so will push back from China’s leaders. So far they have been successful. “The Chinese government is pretty good at buying off intellectuals and the middle class who fear disorder much more than they want political participation,” Mr. Fukuyama said.

He added that he would not be surprised if China and even Russia were to come up with a “new type of authoritarian ideology that tries to justify” their non-Western systems. He has already heard the outlines of such arguments — which echo the “Asian values” idea of non-Western cultural norms that lead to different development paths — from Chinese intellectuals and Russian policy makers.

Where the theorizing spills out of the classroom, though, is around the question of what can be done to influence the process. This is where stark differences appear, not between liberals and conservatives, but between the professors and policy makers. As Mr. Fukuyama said, one point on which he has differed from neoconservatives in the Bush administration is that, “I think, in general, the United States can’t do very much.”