Expectations and the neutrality of interest rates

Our central banks set interest rates, and do not even pretend to control money supplies. How do interest rates affect inflation? We finally have a complete economic theory of inflation under interest rate targets and unconstrained liquidity. Its long-run properties mirror those of monetary theory: Inflation can be stable and determinate under interest rate targets, including a peg, analogous to a k-percent rule.

Uncomfortably, stability means that higher interest rates eventually raise inflation, just as higher money growth eventually raises inflation. Sticky prices generate some short-run non-neutrality: Higher nominal interest rates can raise real rates and lower output. A model in which higher nominal interest rates temporarily lower inflation, without a change in fiscal policy, is a harder task. I exhibit one such model, but it paints a more limited picture than standard beliefs. Generically, without a change in fiscal policy, monetary policy can only move inflation from one time to another.

The last decade has provided a near-ideal set of natural experiments to distinguish the principal theories of inflation. Inflation did not show spirals or indeterminacies at the long zero bound. The large monetary-fiscal expansion of the covid era produced a temporary spurt of inflation. The same money unleashed in quantitative easing had no such effect.