ear [A]The most recent recession in the United States began inDecember of 2007 and ended in June of 2009, according to the official arbiter of recession dating, the NationalBureau ofEconomic Research. However, two years after the official end of the recession, fewAmericans would say that economic troubles are behind us. The unemployment rate, in particular, remains above 9 percent. Some labor market indicators, such as the proportion of long-term unemployed, are worse now than for any postwar recession.　　[B]There are two widely circulated narratives to explain what is going on. The Keynesian narrative is that there has been a major drop in aggregate demanD、According to this narrative, the slump can be largely cured by using monetary and fiscal stimulus.The main anti-Keynesian narrative is that businesses are suffering from uncertainty and over-regulation.According to this narrative, the slump can be cured by having the government commit to and follow a more hands-off approach.　　[C]I want to suggest a third interpretation. Without ruling out a role for aggregate demand or for the regulatory environment, I wish to suggest that structural change is an important factor in the current rate of high unemployment. The economy is in a state of transition, in which the middle-class jobs that emerged after World War II have begun to decline.AsErikBrynjolfsson andAndrew McAfee put it in a recent e-book RaceAgainst the Machine:The root of our problems is not that we’re in a Great Recession, or a Great Stagnation, but rather that we are in the early throes of a Great Restructuring.[D]In fact, I believe that the GreatDepression of the 1930s can also be interpreted in part as an economic transition. The impact of the internal combustion engine and the small electric motor on farming and manufacturing reduced the value of uneducated laborers. Instead, by the 1950s, a middle class of largely clerical workers was the most significant part of the labor force.Between 1930 and 1950, the United States economy underwent a Great Transition.Demand fell for human effort such as lifting, squeezing, and hammering.Demand increased for workers who could read and follow directions. The evolutionary process eventually changed us from a nation of laborers to a nation of clerks.　　[E]The proportion of employment classified as “clerical and kindred workers” grew from 5.2 percent in 1910 to a peak of 19.3 percent in 1980. (However, by 2000 this proportion had edged down to 17.4 percent.) Overall, workers classified as clerical, professional workers, technical workers, managers, officials, and proprietors exceeded 50 percent of the labor force by 2000.Corresponding declines took place in the manual occupations. Workers classified as laborers, other than farm or mine, peaked at 11.4 percent of the labor force in 1920 but were barely 6 percent by 1950 and less than 4 percent by 2000. Farmers and farm laborers fell from 33 percent of the labor force in 1910 to less than 15 percent by 1950 and only 1.2 percent in 2000.　　[F]The introduction of the tractor and improvements in the factory rapidly reduced the demand for uneducated workers.By the 1930s, a marginal farm hand could not produce enough to justify his employment. Sharecropping, never much better than a subsistence occupation, was no longer viable. Meanwhile, machines were replacing manufacturing occupations like cigar rolling and glass blowing for light bulbs.[G]The structural-transition interpretation of the unemployment problem of the 1930s would be that the demand for uneducated workers in the United States had fallen, but the supply remained high. The high school graduation rate was only 8.8 percent in 1912 and still just 29 percent in 1931.By 1950, it had reached 59 percent.3 With a new generation of workers who had completed high school, the mismatch between skills and jobs had been greatly reduceD、　　[H]What took place after the Second World Wa