This paper reevaluates the basic prescriptions of monetary policy design in the new Keynesian paradigm through the lens of imperfect knowledge. We show that while the basic logic of monetary policy design under rational expectations continues to obtain, perfect knowledge and learning can limit the set of policies available to central banks, rendering expectations management in general more difficult. Nonetheless, the desirability of some form of price-level targeting, inducing inertia in interest-rate policy, paramount under rational expectations, is robust to the assumption of imperfect knowledge.

This paper proposes a theory of the fiscal foundations of inflation based on imperfect knowledge and learning. Because imperfect knowledge breaks Ricardian equivalence, the scale and composition of the public debt matter for inflation. High and moderate duration debt generates wealth effects on consumption demand that impairs the intertemporal substitution channel of monetary policy: aggressive monetary policy is required to anchor inflation expectations. Counterfactual experiments conducted in an estimated model reveal that the US economy would have been substantially more volatile over the Great Inflation and Great Moderation periods if US debt levels had been those observed in Italy or Japan.