Discussion of Ben Bernanke’s possible successor has focused on who could best manage the US Federal Reserve’s eventual exit from its multiyear monetary expansion. While President Barack Obama should take that into account, what he should really be looking for in the next chairman is someone who can institutionalise a new policy approach at the central bank and get congressional agreement for doing so.

Like it or not, when Mr Bernanke steps down in January, his replacement will have to make unconventional monetary policy conventional, and establish a viable oversight framework for doing so.

The great lesson of the financial crisis for monetary policy is that there is no one interest rate that determines or even represents credit conditions in the modern economy. For the past 30 years, both monetary economics and policy making have made the comforting assumption that movements in the central bank’s main policy interest rate would affect the whole economy in a predictable way. This allowed academic and market analysts to try to explain central bank behaviour in terms of simple rules.