Prior to Friedman's Philips Curve research, generally accepted wisdom held that an economy could essentially choose how to trade off inflation with unemployment.
Friedman is also noted for developing the Philips Curve, an economic model that noted the inverse relationship between the rates of unemployment and inflation.
Monetarists correctly argued that inflation is always a monetary phenomenon, but the newly revived theory that was long ago dismissed even by Friedman is merely a variation of the much discredited Phillips Curve.