Federal Reserve Bank of Minneapolis Research Department Sophisticated Monetary Policies

The Ramsey approach to policy analysis finds the best competitive equilibrium given a set of available instruments. This approach is silent about unique implementation, namely designing policies so that the associated competitive equilibrium is unique. This silence is particularly problematic in monetary policy environments where many ways of specifying policy lead to indeterminacy. We show that sophisticated policies which depend on the history of private actions and which can differ on and off the equilibrium path can uniquely implement any desired competitive equilibrium. A large literature has argued that monetary policy should adhere to the Taylor principle to eliminate indeterminacy. Our findings say that adherence to the Taylor principle on these grounds is unnecessary. Finally, we show that sophisticated policies are robust to imperfect information. ∗Atkeson, University of California, Los Angeles, Federal Reserve Bank of Minneapolis, and NBER; Chari, University of Minnesota and Federal Reserve Bank of Minneapolis; Kehoe, University of Minnesota, Federal Reserve Bank of Minneapolis, and NBER. Atkeson, Chari, and Kehoe thank the National Science Foundation for financial support and Kathleen Rolfe for excellent editorial assistance. The views expressed herein are those of the authors and not necessarily those of the Federal Reserve Bank of Minneapolis or the Federal Reserve System. Frank Ramsey proposed a now classic approach to policy analysis under commitment. This approach speci es the set of instruments available to policymakers. The Ramsey problem is to nd the competitive equilibrium that maximizes social welfare with the given set of instruments. Barro (1979), Lucas and Stokey (1983) among many others have extended this approach to situations with uncertainty by specifying the instruments as functions of exogenous events. This extension has made the approach very useful in addressing policy questions in macroeconomics. While the Ramsey approach has been very useful in characterizing the best competitive outcomes, by itself it is not an operational guide to policy in the sense that it does not tell policy-makers how to conduct policy for all possible histories. An approach that is an operational guide would specify policies for every history and would describe what the corresponding outcomes will be for every history. Here we extend the language of Chari and Kehoe (1993) to an environment in which the policymaker has commitment in order to specify policies after every history and to describe continuation outcomes after every history. In our approach, we allow policies to depend on the history of past actions by private agents and allow them to di¤er on and o¤ the equilibrium path. We label such policies sophisticated policies and label the resulting equilibrium a sophisticated equilibrium. In many macroeconomic models, especially monetary models, many ways of specifying policies lead to indeterminacy and therefore could lead to undesirable outcomes. In such models the question of pressing interest is, Can policies be speci ed as operational guides which tell policymakers what to do after every history and which lead a desired outcome to be the unique equilibrium outcome? If we can, then we say the policy uniquely implements the desired outcome. In this paper we study two standard monetary economies: a simple model with one period price setting and a model with Calvo price setting. The main contribution in this paper is to show that, under su¢ cient conditions, any outcome of a competitive equilibrium can be uniquely implemented by appropriately chosen sophisticated policies. Our ndings are of particular relevance to monetary policy. The simplest way of applying the Ramsey approach to policy-making is to nd the desired competitive equilibrium, which speci es policy as a function of exogenous events, and use that function for policy. This way of describing policies is problematic in monetary policy environments in which policymakers use short-term interest rates as their principal monetary policy instrument. The reason is that, since at least the early work of Sargent and Wallace (1975), researchers have been aware that policies which make interest rates functions only of exogenous events can lead to indeterminate outcomes. Such policies could lead to the best equilibrium but they could also lead to undesirable outcomes including hyperination and outcomes with excessive volatility due to sunspot-like uctuations. In this sense, policies which lead to indeterminacy are risky and researchers generally agree that such policies should be avoided. This concern with the risks arising from indeterminacy has led to a substantial literature which is aimed at nding policy rules which eliminate indeterminacy. (See, for example, McCallum 1979 and for some recent work see Woodford 2003.) The recent literature argues that interest rate rules should follow the Taylor principle: interest rates should rise more than one-for-one with a rise in ination rates relative to target ination. The reasoning is that an interest rate rule that obeys the Taylor principle leads to unique outcomes while a rule that violates it leads to indeterminacy. A related literature argues that the undesirable ination experiences of the 1970s in the United States was due in large part to the failure of monetary policy to obey the Taylor principle in that time period. (See, for example, Clarida, Gali, and Gertler (2000). ) Our nding that sophisticated policies can implement any equilibrium outcome implies that such policies can implement outcomes which violate the Taylor Principle along the equilibrium path as well as those which obey such a principle along the equilibrium path. Since sophisticated policies can uniquely implement any desired competitive equilibrium it follows that adherence to the Taylor principle is not needed for uniqueness. Moreover, our ndings imply that historical evidence that policy violated the Taylor principle in some periods does not necessarily imply that such policy was unwise. Our paper is also related to previous papers that address problems of indeterminacy in monetary economies (see Wallace 1981, Obstfeld and Rogo¤ 1983, Benhabib, Schmitt-Grohe, Uribe 2001, Christiano and Rostagno 2001, King, 2001, and Svensson and Woodford, 2005). Read at face value these papers pursue a di¤erent approach to implementation that we refer to as implementation via nonexistence. The idea is to specify policies so that for all outcomes