He makes some good additional points:
Here are some criticisms that come to mind.
1. If “the” full-employment real interest rate is negative, then why do we need quantitative easing? Why does not the excess of saving over investment not by itself drive long-term rates to zero?
2. Summers wants to claim that full employment has been achieved in recent years because of asset bubbles. However, in a world of negative real interest rates, there is no such thing as an asset bubble. Real assets have infinite value in such a world.
The full post is here.