 For that, we still need Marx or his modern-day equivalent".Harvey also takes Piketty to task for dismissing Marx's "Das Kapital" without ever having read it.IMF economist Carlos Góes researched the basic thesis put forth by the book - that when the rate of return on capital ("r") is greater than the rate of economic growth ("g") over the long term, the result is concentration of wealth - and found no empirical support for it; in fact, an opposite trend was identified in 75% of the countries studied in depth.