In his best-selling book "Capital in the Twenty-First Century," Thomas Piketty argues that capitalism aggravates inequality through several mechanisms, all of which are based on the notion that r (the return on capital) falls less quickly than g (growth in income).

While debate about Piketty's work has focused largely on the advanced economies, this fundamental concept fits China's recent experience, and thus merits closer examination.

Of course, a large share of China's population has gained from three decades of unprecedentedly rapid GDP growth. The fixed-capital investments that have formed the basis of China's growth model largely have benefited the entire economy; infrastructure improvements, for example, have enabled the rural poor to increase their productivity and incomes.