Graduates from Columbia University's School of Business hold a sign as they cheer during university's commencement ceremony in New York

With Thomas Piketty’s book, Capital in the 21st Century, rising to number 1 on best-seller lists, inequality has become central to the public debate over economic policy. Piketty, and much of this discussion, focuses on the sharp increases in the share of income and wealth going to the top 1 percent, .1 percent and .01 percent of the population.

This is indeed a critical issue. Whatever the resolution of particular numerical arguments, it is almost certain that the share of income going to the top 1 percent of the population has risen by 10 percentage points over the last generation, and that the share of the bottom 90 percent has fallen by a comparable amount. The only groups that have seen faster income growth than the top 1 percent are the top .1 percent and top .01 percent.

Applications are seen at a rally held by supporters of the Affordable Care Act in Jackson, MississippiThis discussion helps push policy in constructive directions. Taxes can be reformed to eliminate loopholes and become more progressive, while also promoting a more efficient allocation of investment. In areas ranging from local zoning laws to intellectual property protection, from financial regulation to energy subsidies, public policy now bestows great fortunes on those whose primary skill is working the political system rather than producing great products and services. There is a clear case for policy measures to reduce profits from such rent- seeking activities, as a number of economists, notably Dean Baker and the late Mancur Olsen, have emphasized.

Unless one regards envy as a virtue, the key reason for concern about inequality is that lower- and middle-income workers have too little — not that the rich have too much. So in judging policies relating to inequality, the criterion should be what their impact will be on the middle class and the poor. On any reasonable reading of the evidence starting where the United States is today, more could be done to increase tax progressivity without doing any noticeable damage to the prospects for economic growth.

It is important to remember, however, that important aspects of inequality are unlikely to be transformed just by limited income redistribution. Consider two fundamental components of life: health and the ability to provide opportunity for children.