...behind flexible inflation targeting. It is OK to have a target based on inflation alone, with no mention of the output gap, because you cannot in the long run keep inflation at target without also keeping the output gap at zero. This is sometimes called the divine coincidence. However if, at low inflation rates, inflation becomes a noisy, weak and asymmetric indicator of the output gap, then focusing on inflation is going to perform badly. In these circumstances it could be many years before it becomes clear that we have been continually running the economy under capacity, and needlessly wasting resources. Unfortunately even when that point of realisation arrives, for obvious reasons monetary policymakers are going to be reluctant to acknowledge the mistake.