Yet in jointly honoring the work of Mr. Fama and Mr. Shiller, the committee also highlighted how far the economics profession remains from agreeing on the answer to a basic and consequential question: How do markets work?

“It encapsulates the state of modern economics,” said Justin Wolfers, an economist at the University of Michigan. “We have big important questions that remain largely open and we have giants bringing evidence to bear. And the answer turns out to be more complicated than markets are efficient — or markets are inefficient.”

The dispute is not merely academic. The deregulation of financial markets beginning in the 1980s was justified by the view that markets are rational and efficient. Complacence about rising home prices in the 2000s similarly reflected the view that prices are inherently rational. In the aftermath of the crisis, conversely, the work of Mr. Shiller and other proponents of behavioral economics — the integration of psychology into economic models — has been influential in shaping an intensification of financial regulation. And Federal Reserve officials are now debating whether bubbles can be identified and when they should be popped.

Mr. Fama, 74, was honored for showing in the 1960s that asset prices are “extremely hard to predict over short horizons.” He has said the seeds of his theory were planted as an undergraduate at Tufts University, while working for a professor who ran a stock market forecasting service. Mr. Fama was charged with devising and testing forecasting schemes, which invariably failed to work. He later coined the term "efficient markets" to describe his view that asset price movements could not be predicted because prices fully reflected all available information.

The theory basically asserted, in the words of the economist Burton Malkiel, that “a blindfolded monkey throwing darts at a newspaper’s financial pages could select a portfolio that would do just as well as one carefully selected by experts.”

It has been repeatedly validated, sometimes in experiments involving actual monkeys. And while many market prognosticators on Wall Street still thrive in part by claiming that they can offer investments that will consistently beat the market averages, Mr. Fama’s well-established theory has influenced the way millions of people now invest, contributing to the popularity of index funds that hold broad, diversified baskets of equities.

Mr. Shiller, 67, introduced in the early 1980s an important limitation on the idea that markets operate efficiently. He showed that the volatility of stock prices was greater than the volatility in corporate dividends. Moreover, he found that some of those irrational deviations fell into predictable patterns.