In the comments on this post, he suggests a possible way to reconcile secular stagnation with a high return on capital.
One way to reconcile the two is to say that Piketty’s return on capital includes the equity premium (and other premia for privately held businesses, etc.), whereas the secular stagnation idea of a perpetual ZLB deals with only the riskfree rate.
Some remarks:
1. Fischer Black said that finance is about time and risk. The risk-free rate is the price of time. The equity premium might be a proxy for the price of risk.
2. In Keynesian terms, perhaps one can think of a low risk-free rate as reflecting the desire to hoard and a high risk premium as reflecting low animal spirits.
3. As Matt notes, this approach to reconciling secular stagnation with a high return on capital implies that those earning the high returns are being rewarded for taking risks in an economy in which such risk-taking is scarce. Picketty seems to be pretty confident that high earners will not change their behavior much in response to higher taxes. Perhaps this might be true of labor supply. But can one rule out a significant dampening effect on risk-taking?
Read Matt’s entire comment. As he points out, the secular stagnation story is difficult to reconcile with some fairly basic calculations concerning capital and investment.