Early in the expansion, for example, we kept rates unusually low for an extended period, when financial sector fragility held back the economy. Most recently we have needed to raise rates to relatively high levels in real terms in response to the side effects of accelerating growth and related demand-supply imbalances.
Variations in the stance of policy - or keeping it the same - in response to evolving forces are made in the framework of an unchanging objective - to foster as best we can those financial conditions most likely to promote sustained economic expansion at the highest rate possible. Maximum sustainable growth, as history so amply demonstrates, requires price stability.