Professor Solow's article, “Technical Change and the Aggregate Production Function,” now virtually classic, has made a great impact on economists generally and in the last few years the subject has received unprecedented attention in economic literature. The reason for this extraordinary emphasis on “Technical Change” has been the conclusion—in Solow's above-mentioned article—based on statistical evidence, that gross output per man-hour in the United States nonfarm economy doubled over the period 1909–1949, “with 87.5 percent of the increase attributable to technical change and the remaining 12.5 percent to increased use of capital.”