Hannes Malmberg commented on my review of Saez and Zucman in response to a point I made about the elasticity of capital supply:

I think you are confusing demand and supply elasticities of capital.

The revenue calculations hinge on the elasticity of capital supply, i.e., how fast capital supply rise with the interest rate (how much more do people decide to save).

The Piketty spiral, in contrast, hinges on the elasticity of capital demand, i.e., how fast the interest rate fall with increasing capital (i.e., how fast firms and companies switch away from using capital when it gets more expensive).

There is nothing theoretically preventing us from having an almost horizontal capital demand curve, and an almost vertical capital supply curve. In such a world, a capital tax raises a lot of revenue, but increasing the savings propensity increase the capital stock without reducing the interest rate. (...)

I think he is basically right, and I'll partially retract section 3A of my