In 1849, the Scottish essayist Thomas Carlyle labeled economics the “dismal science.” Two centuries later, contemporary practitioners still study dismal choices: Higher prices or fewer jobs? Spend or save? They have also become a smug lot.

Economists take pride in the sophisticated statistical techniques on which they rely to analyze phenomena such as growth, inflation, unemployment, trade, and even the long-term effects of abortion on crime rates. Many are convinced that their methods are more rigorous than those of all other social sciences and dismiss research that does not rest on quantitative methods as little more than “storytelling” or, worse, “glorified journalism.” Anthropologists, some economists jest, believe that the plural of anecdote is “data.”

A survey published in the Journal of Economic Perspectives found that 77 percent of the doctoral candidates in the leading departments in the United States believe that “economics is the most scientific of the social sciences.” It turns out, however, that this certitude does not stem from how well they regard their own discipline but rather from their contempt for the other social sciences. Although they were nearly unanimous about the relative superiority of their profession, only 9 percent of the respondents were convinced that economists agree on fundamental issues.

And they are right. Economists today are still grappling with basic questions for which they have no answers. Much more than fodder for academic squabbles, this uncertainty often has serious consequences. When economists err in theory, people suffer in practice. Fernando Henrique Cardoso, Brazil’s former president, recalls that in the midst of his country’s financial crisis, he received calls from experts at the International...