But others have put forward the view that monetary policy should only care about price stability, without any direct concern with output. The origins of this can be found in Friedman’s monetarism (he was, of course, concerned above all with price stability). It seems only a minor elision to slip from monetarism to a single objective for monetary policy.
But the point to note here is that the old monetary rules had an important element of income smoothing built into them -- when output slowed in the course of the cycle, money supply rules produced a more-or-less automatic easing of monetary policy, because the central relationship was between money and nominal income.