It isn't very often that a serious book on economics becomes a bestseller, but on Saturday evening, French scholar Thomas Piketty's Capital in the 21st Century was No 1 on the Amazon list. In a highly regarded review in the New York Review of Books, fellow economist Paul Krugman predicted that Piketty would soon become a household name. He has caused "a revolution in our understanding of long-term trends in inequality," Krugman explained.

As Piketty told Qz.com recently, because the return on investment tends to exceed the rate of growth, inequality isn’t an unintended consequence but an inevitable part of capitalism. This means that higher taxes on wealth are required to protect democratic society.

Listen to him explain his ideas here.