1. Introduction Monetary authorities who choose to reduce their country's rate of inflation, that is, to disinflate, are usually faced with subsequent recessions. A pattern of slower growth in the money supply, followed by a lower inflation rate and lower output, can be seen in historical statistics, such as those examined by Friedman and Schwartz (1963). When there was thought to be a permanent Phillips curve trade-off between inflation and unemployment, an important policy question was what combination of inflation and unemployment was most desirable. As economists came to accept the idea of a short-run but not a long-- run trade-off between inflation and unemployment, the stage was set to ask about how much output is lost as a result of a disinflation. Okun (1978), using results from several econometric models, estimated that an extra 1% unemployment rate for one year would reduce inflation between one-sixth and one-half of 1%. To reduce inflation by 1%, these figures suggested that the unemployment rate needed to be higher by 2 to 6% of the labor force. If one uses an "Okun's law" of 2.5% of gross national product (GNP) lost for an unemployment rate higher by 1%, then the output lost to reduce inflation by 1% would be between 5 and 15% of GNP. The term "sacrifice ratio" is now widely understood to mean the ratio of the cumulated percentage loss of output (at an annual rate) to the reduction in the trend rate of inflation.1 For the disinflation in the early 1980s in the United States, Fischer (1986) figures the sacrifice ratio was about five. Other empirical studies, such as those in Ball (1994b) and Jordan (1997), find a range of estimates around an average sacrifice ratio of about two.2 The pattern of slower rates of growth in the money supply being followed by recessions has posed a challenge to theorists to develop plausible models that help us understand this phenomenon. The existence of staggered price setting is one candidate explanation, and Taylor (1979, 1980) deserves credit for introducing formal analyses of how overlapping wage contracts can lead to a persistence in wages and deviations in output from its natural rate during disinflations. Sargent (1983), in discussing conditions for a successful disinflation without much output loss, characterizes the Taylor model as follows: "In this class of models, in terms of unemployment it is costly to end inflation because firms and workers are now locked into long-term wage contracts that were negotiated on the basis of wage and price expectations that prevailed in the past. . . . In addition, the wage contracting mechanism contributes some momentum of its own to the process, so that the resulting sluggishness in inflation cannot be completely eliminated or overcome by appropriate changes in monetary and fiscal policies" (p. 55). Similarly, Vegh (1992), explaining why ending hyperinflations appears to involve less output loss than ending moderate inflations, writes, "The fact that in hyperinflations backward-looking contracts (so prevalent in industrial and chronic-inflation countries) disappears is probably at the heart of the difference in output costs" (p. 656). In a widely used textbook, Romer (1996, p. 273) writes that "the Taylor model exhibits price level inertia: the price level adjusts fully to a monetary shock only after a sustained departure of output from its normal level. As a result, it is often claimed that the Taylor model accounts for inflation inertia." Romer then adds the provocative sentence: "Ball (1994a) demonstrates, however, that this claim is incorrect." The link between the discrete-time model presented by Romer and the contention attributed to Ball is not immediately evident and needs to be clarified. Beginning with an environment of steady growth in money and prices, Ball (1994a) assumes that a new regime suddenly announces a fully credible continuous linear decline in the growth rate of money. …