While the theory of economic progress offered by Piketty is the assertion that economic progress is the result either of totally unexplained “productivity growth” or productivity growth based on technological progress divorced from capital accumulation, the truth is that a rise in the productivity of labor and concomitant economic progress almost always requires an increase in the supply of physical capital goods relative to the supply of labor. For example, a larger supply of iron ore per steel worker is essential for steel workers being able to produce more steel per worker, as is a larger, better supply of capital goods in the form of the plant and equipment used by the steel workers. The same, of course, is true of the appropriate supplies of capital goods in every branch of production.