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The prom& of InstitutionabtTheory ~ I n his usual direct way, John J. Mearsheimer has sharpened the theoretical issues dividing realist from institutionalist theory, and for this service we are grateful. We are also pleased that he has read the institutionalistliterature so thoroughly. He correctlyasserts that liberal institutionalists treat states as rational egoists operating in a world in which agreements cannot be hierarchically enforced, and that institutionalists only expect interstate cooperation to occur if states have significant common interests. Hence institutionalist theory does not espouse the Wilsonian concept of collectivesecurity-which Charles and Clifford Kupchan refer to as "ideal collective security"-critiqued so well by I.L. Claude thirty years ago.' Nor does institutionalism embrace the aspirations to transform international relations put forward by some critical theorists. Like realism, institutionalist theory is utilitarian and rationalistic.2 However, Professor Mearsheimer's version of realism has some rather serious flaws. Among them are its penchant for assertions that turn out to be incorrect; its propensity to privilege its own viewpoint, so that in the absence of decisive evidence either way it invariably seems to prevail; its failure to explicate the conditions for the operation of its generalizations;and its logical contradictions,escaped only through verbal sleight-of-hand.We will begin by pointing out such errors from his own recent articles in this journal, then Robert 0.Keohane and ~i~~L. Martin Robert 0.Keohane is Stanfield Professor of International Peace, Harvard University, and author of After Hegemony: Cooperation and Discord in the World Political Economy (Princeton University Press, 1984). Lisa L. Martin is John L. Loeb Associate Professor of Government, Harvard University,and author of Coercive Cooperation: Explaining Multilateral Economic Sanctions (Princeton University Press, 1992). The authors thank Marc Busch, Chris Gelpi, Andrew Moravcsik, and Celeste Wallander for their valuable comments on an earlier version of this essay. 1. Inis L. Claude, Power and International Relations (New York Random House, 1962).Mearsheimer relies heavily on Claude's critique in his own discussion of collective security. 2. See Richard K. Ashley, "The Poverty of Neorealism," International Organization, Vol. 38, No. 2 (Spring 1984),pp. 225-286. Ashley included Robert 0.Keohane as one of the "neorealists" whose "orrery of errors" he rejected. The fact that Mearsheimer criticized institutionalism and critical theory in the same article should not, therefore, lead readers to believe that there is an intellectual affinity between these two schoolsof thought. However,the work of "constructivist" theorists such as Alexander Wendt eloquently makes a number of arguments that many institutionalists would accept. International Security, Vol. 20, No. 1 (Summer 1995),pp. 39-51 0 1995by the President and Fellows of Harvard College and the Massachusetts Institute of Technology 39 International Security 20:1 1 40 examine his major claims about institutionalism. We consider the illusory divide between security and economic issues, the muddled question of “relative gains,” and empirical work (admittedly in its early stages) that provides evidence of the significance of international institutions. We conclude that institutions sometimes matter, and that it is a worthy task of social science to discover how, and under what conditions, this is the case. The Fallacious Logic of Realism Five years ago Professor Mearsheimer forecast the imminent decline of NATO: “It is the Soviet threat that holds NATO together. Take away that offensive threat and the United States is likely to abandon the Continent, whereupon the defensive alliance it headed for forty years may di~integrate.”~ At the same time, he predicted that ”the EC is likely [due to the end of the Cold War1 to grow weaker, not stronger with time.”4 Yet now that both NATO and the European Community, now the European Union (EU), are expanding their memberships, and hardly in decline, he abandons specificity for the equally false but more difficult to falsify generalizationthat “institutionshave minimal influenceon state behavior and thus hold little prospect for promoting stability in a post-Cold War ~ o r l d . ” ~ Professor Mearsheimer demands proof that international institutions matter. Yet he begins his articleby reminding us that major governments recently have been emphasizing the value of international institutions; he could have added that they invest significant material and reputational resources in NATO, the EU, and also in...