THE origins of the current economic crisis can be traced to a particular kind of social epidemic: a speculative bubble that generated pervasive optimism and complacency. That epidemic has run its course. But we are now living with the malaise it caused.
News accounts of the economic crisis rarely put it in these terms. They tend to focus on distinct short-term developments or on the roles of prominent people like Federal Reserve governors, members of Congress or Wall Street financiers. These stories grab attention and may be supported by some of the economic statistics that the government and private institutions collect.
But the economic situation is primarily driven by hard-to-quantify sociological factors that play out over many years.
A half-century ago, there was a lively discussion among economists about the dynamics of price expectations. For example, Alain C. Enthoven, then of the Massachusetts Institute of Technology, and Kenneth J. Arrow of Stanford wrote in 1956 that expectations that extrapolate past price increases can produce economic instability. But that thinking was largely cast aside in the 1960s, when my profession embraced the theory that efficient markets formed by people holding rational expectations could explain virtually all economic activity.
As a result, economists in recent decades have not developed expectations theory much further. That needs to be corrected in coming years. In the meantime, this failing helps explain why the current crisis was generally unpredicted, and why its future course is so poorly understood.