In central banking circles, the talk of normalisation has been under way for some time. The Federal Reserve and the Bank of England have both moved interest rates off the lowest levels they hit after the great recession. At the European Central Bank, Mario Draghi has now begun to talk about the path for interest rate increases in the eurozone in order to shape expectations for a moderate tightening process.

“Normalisation” means “going back to normal”. But what, precisely, does that mean? If “normal” means the pre-crisis norm, there are many ways in which that differs from today. So here are four senses in which one could aim to “get back to normal” — and in all four, doing so is either undesirable or meaningless.

First and most simply, people sometimes use normalisation to mean getting back to a “normal” level of central bank interest rates. This is silly. Central banks should aim to set the rates that are most conducive to fulfilling their public mandate. There are many reasons — including persistently benign inflation and a lower “natural” rate (at which desired savings and investment match) — why central bank interest rates should stabilise permanently below where they were before the crisis.