By Joseph Stiglitz, adapted from a white paper published in May by the Roosevelt Institute, where he is chief economist. Stiglitz received the 2001 Nobel Prize in Economics.

Americans are finally beginning to appreciate the magnitude of the inequalities in income and wealth that mark our society. Lately, this realization has been helped along by an unexpected source: the French economist Thomas Piketty, whose Capital in the Twenty-First Century is the surprise bestseller of the year. Piketty has collected the most extensive evidence available of the increases in economic inequality and inherited wealth over the past forty years, which…