Rationalism and the “rational actor assumption” in realist international relations theory

The commitment to the rational actor model of state behavior is said to be a core assumption of realist theory. This assumption is listed in most textbook accounts of realism. Yet is rationality a core supposition of realist theory, and if so, what kind of rationality is implied in these claims? Debate on the relationship between realism, and what is often labeled as rationality is replete with misunderstandings. Authors deploy terms such as rationality, rationalism, and rational actor in diverse and contradictory ways. This article aims to cut through this confusion and provide an account of the different ways in which these terms are used in the field of International Relations (IR). We argue that much of the confusion surrounding rationalism/rationality in IR arises due to a failure to distinguish between rationalism as an epistemological position (the observer rationality assumption) and rationality as an ontological position (the rational actor assumption). We use this distinction to examine carefully the relationship between the concepts of rationalism/rationality in realist theory.


Introduction
A core assumption of realist theory is said to be the commitment to the rational actor model of state behavior. This assumption is listed in most textbook accounts of realism.
Recently, however, some mainstream realists, such as John Mearsheimer, have begun to question whether this assumption applies only to certain forms of realism, but not to others. In particular, Mearsheimer (2009) has suggested that the influential structural realism of Kenneth Waltz has no commitment to the "rational actor assumption." 1 Bessner and Guilhot (2015) provide support for this denial of the relationship between Waltz and the "rational actor assumption." According to Bessner and Guilhot, Waltz explicitly rejects the "rational actor assumption" on the basis of his commitment to systems theory and his desire to exclude any form of decisionism in structural realism.
We think these claims are wrong. Indeed, if realism were to reject one of its core assumptions, such as the rational actor model of state behavior, then it is not clear what is left of the theory. In their critique of realism as encompassing the assumptions of rival paradigms, Legro and Moravcsik (1999: 6) argue that there are two core assumptions of "minimal realism": anarchy and rationality. With respect to the rationality assumption, Legro and Moravcsik (1999: 12) maintain that realists assume that the units "are rational in the conventional sense that they select a strategy by choosing the most effective available means to achieve their ends, subject to constraints imposed by environmental uncertainty and incomplete information." Theories cannot be stripped of their core assumptions without also abandoning the research program itself (Lakatos et al., 1978). Despite Waltz claiming to have little time for the concept of rationality, his theory only makes sense if it assumes that states do act rationally and follow the demands and incentives of the structure of the system. Waltz does not have to believe that states always act rationally, but he does have to assume that if states do not adapt their behavior to the demands of the system, then the system will punish them. As such, his theory has no specifiable outcomes if stripped of the "rational actor assumption." As Glaser (2010: 2) explains, "Evaluation of this rational-state versus rational-state interaction lies at the heart of the entire neorealist/structural-realist international relations theory project, as the major works incorporate either a rationality assumption or an evolutionary mechanism that selects out states that behavior [sic] irrationally." Debate on the relationship between realism and rationalism is replete with confusion. Authors deploy terms such as rationality, rationalism, and rational actor in diverse and contradictory ways. This article aims to cut through this confusion and provide an account of the different ways in which these terms are used. A supplementary aim of the article is to examine carefully the relationship between the concept of rationality and realist theory. In doing so, our goal is to provide a degree of order concerning the general confusion that exists about this important relationship. The issue also has important consequences for those approaches that reject so-called rationalist forms of theorizing. Despite the decline of the inter-paradigm debate the distinction between rationalist and supposedly nonrationalist theorizing remains one of the most enduring in IR. But we can only assess objections to rationalism if we have a clear sense of what is meant by those using the term. Thus, although this article's central question is to explore the relationship between rationality in realist theory, the implications of this analysis go beyond realism.
Claims about rationality in realism, and among the critics of realism, confuse two different meanings of the term. The first is an ontological claim, or assumption, about the nature of the actors in the system; the "rational actor assumption." Some authors (Rathbun, 2019) argue that there is an important distinction between the instrumental rationality assumed in rational choice theory and the judicious, enlightened decisionmaking involving the use of reason that Morgenthau, for example, embraces. We do not think this is a valid distinction. Instrumental rationality in rational choice theory may be more formally circumscribed, but it still relies on a strategic consideration of the best course of action taken after a consideration of the context framing the decision, orientated toward the achievement of some desired end. This is exactly the same as the kind of rationality (pragmatism) that Morgenthau defends. In this respect, both forms of rationality are identical. They refer to the ontological property (rationality) an actor is assumed to possess in order to assess the best options in a given situation to achieve a given end. Both are means/ends orientated. The second is an epistemological claim, or assumption, about the possibility of developing a rational theory of international politics. As Morgenthau (1946: 3)

writes in Scientific Man:
Aside from the continuing influence which the original rationalistic philosophy exerts in our civilization under the guise of scientific terminologies, seventeenth and eighteenth century rationalism and the mode of thought prevailing in the nineteenth and twentieth centuries have, however, two qualities in common, both of which are rooted in rationalistic assumptions; the conception of the social and the physical world as being intelligible through the same rational processes, however, these processes are to be defined, and the conviction that understanding in terms of these rational processes is all that is needed for the rational control of the social and physical world.
Although Morgenthau was deeply critical of this version of "rationalism" in Scientific Man, he eventually came to embrace a form of it in Politics Among Nations. Famously, Morgenthau (1955: 4) announced that "Realism, believing as it does in the objectivity of the laws of politics, must also believe in the possibility of developing a rational theory that reflects, however imperfectly and one-sidedly, these objective laws." For the sake of clarity, we will refer to this as the "observer rationality assumption" to distinguish it from the "actor rationality assumption." In unpacking this issue, we aim to illuminate what this controversy means not only for realist theory in particular, but also for disciplinary understandings of rationalist IR theory in general. We begin by examining the existing literature and review the different ways in which terms such as rationality, rationalism, and the "rational actor assumption" are used. In section two, we examine the role that the "rational actor assumption" plays in both the classical realism of Morgenthau and the structural realism of Mearsheimer and Waltz. We differentiate between some of these uses and provide an explanation of why the confusion occurs. Finally, we conclude by arguing that both the "rational actor assumption," and the assumption of "observer rationality" demonstrate how realist theory is best understood as a normative theory of how states "ought" to behave and not as a theory of how they do behave. As Glaser (2010: 2-3) notes, states do not always behave rationally, but realist theory suggests that those that do produce the most optimal outcomes for themselves and the system. Realist claims about state rationality are injunctions about how states should behave, not about how they do behave. This makes realism a normative theory. This is not a particularly new claim, but it is worth restating, given textbook claims that realism is a set of objective claims about the world (Carr, 1964;Glaser, 2010;Kennan, 1951;Morgenthau, 1955;Scheuerman, 2011;Tucker, 1970).
There are five main reasons that we mostly concentrate on Morgenthau, Waltz, and Mearsheimer. We do, however, also consider the work of other realists including neoclassical realists who have focused on the concept of rationality. First, it is in Morgenthau that the confusion between the ontological assumption of a rational actor and the epistemological assumption of a rational observer first emerges. Second, these are the most influential proponents of classical and structural realism respectively, and it is important to demonstrate how these issues play out in the primary, not the secondary literature. Third, if the confusion begins with Morgenthau, it is in Mearsheimer's recent attempt to distance Waltz's structural realism from the rational actor assumption that the debate is most clearly articulated. Mearsheimer is not the only realist who has raised questions about the rationality assumption in Waltz's theory. Even though Waltz's structural realism had a profound influence on the field of International Relations, his theory has been open to multiple interpretations and a source of endless debate. The most recent controversy has focused on Waltz's understanding of rationality and the question of whether or not his theory employs the rational actor assumption. We believe that it is fundamentally important to clarify Waltz's position on the role that rationality has on his theory. Fourth, if we can make the case in relation to these key authors then the argument has implications for all theorists working in that tradition. Fifth and perhaps most importantly, all recent attempts (Fearon, 1995;Glaser, 2010;Rathbun, 2019) to develop the concept of state rationality do not alter the fundamental premise of the rational actor assumption, which views states as strategic actors (means) orientated toward desired outcomes (ends). Or, as Glaser (2010: 2) puts it, "The state is assumed to be rational-it makes purposive decisions that take reasonable account of its interests, and the international constraints and opportunities that it faces." A careful reading of the work of these prominent realists leads to the conclusion that international politics would be more harmonious and peaceful if only states could act in a rational manner (the rational actor assumption), and that "observer rationality" is what makes this point epistemologically compelling. In fact, as it turns out, most realists, especially Waltz, argue that states do not typically act in rational ways, but that they should. As such, realism is a set of injunctions about how states should act, and not, an objective theory of how states do act.

Differentiating rationality, rationalism, and rational choice
As evidenced by the literature in the field, the meaning of rationality is not self-evident. Determining if realism is a rationalist theory is made more difficult by the fact that IR theorists use the word rationality in different ways. In international relations theory there are three primary concepts that are often invoked when discussing the issue. These are rationalism, rationality, and the "rational actor assumption." 2 The differences between these concepts are not clearly articulated, and scholars mean diverse things when they use them. In this section, we aim to demonstrate not only how these concepts can refer to different things, but also to provide an explanation of why these confusions occur and demonstrate the impact they have on a range of important debates in the discipline.
We argue that rationality (sometimes termed rationalist, or rational), is the broadest of these uses and the most problematic, and hence least useful in terms of nuanced theoretical debate. Unfortunately, it is also the term most often used when discussing realism.
For example, it is commonplace to see claims such as that of Schweller and Wohlforth (2000: 70) who write that "although some realist theories make strong assumptions about rationality, such assumptions are not essential to realism." Schweller and Wohlforth go on to claim that "neorealism is not a rationalist theory of state behavior." But what does rationalist mean in this context?
To claim that realism is a rationalist theory of state behavior can be taken to mean that the theory assumes that states, or state leaders, act rationally. In effect, this form of rationality assumes a "rational actor" model of state behavior. This is an ontological claim about the nature of actors. But this is not the only understanding of rationality that is possible. In Scientific Man Versus Power Politics, for example, Morgenthau (1946) uses the term rationalism in a very specific epistemological manner. This kind of rationality is a commitment, assumed, or explicitly defended, to the Enlightenment view that international politics can be explained in a rational manner. Although often conflated, these two "rationality" assumptions are quite different and should be clearly distinguished. Unless they are distinguished it is impossible to know what Schweller and Wolforth mean when they claim the strong assumptions about rationality are not essential not realism.
In particular, they need to be differentiated because one, the "rational actor assumption" represents an ontological claim, whereas the other, rationalism, expresses a particular set of methodological and epistemological positions. For the sake of clarity, we call the first the "rational actor assumption" and the second the "observer rationality assumption." The "rational actor assumption" refers to properties of the actors that are the subject of study, the "observer rationality assumption" refers to potential for an accurate (objective) study of the subject matter. In most cases, those who embrace the "observer rationality assumption" also embrace the "rational actor assumption"; that states act rationally is a condition of possibility for an objective theory of international politics. The reverse is not always the case. It is possible to accept the "rational actor assumption" yet reject the proposition that a rational (objective) theory of international politics is possible. Williams (2005), for example, seems to accept a limited version of the "rational actor" assumption, yet rejects the "observer rationality assumption" to build his version of "wilfull realism." Rationalism and the rational actor assumption in IR theory As Kahler (1998: 920) notes, "at the time of its entry into American intellectual life, the relationship between realism and rationalism in politics was more confrontational than complementary." Hans Morgenthau, for example, uses the term rationalism in a very specific epistemological manner. In many respects Morgenthau equates rationalism with a determined, one might say messianic, commitment to scientism. Morgenthau also considered rationalism to be a defining feature of Liberal Utopianism. According to Morgenthau (1946: 10): the principles of scientific reason are always simple, consistent, and abstract; the social world is always complicated, incongruous, and concrete. To apply the former to the latter is either futile, in that the social reality remains impervious to the attack of the 'one-eyed reason, deficient in its vision of depth'; or it is fatal, in that it will bring about results destructive of the intended purpose.
Two things are worthy of note here. First, Morgenthau is incorrect to suggest that the principles of scientific reason are simple, consistent, or abstract. The idea that science is simple, consistent, and abstract probably comes from Morgenthau's belief that positivism is the dominant theory of science. As such, Morgenthau was not rejecting science per se, but the positivist account of it. But accounts of the practice of science long ago moved away from the simplistic vision presented by positivism. Current wisdom in the philosophy of science suggests that science is messy, fluid, dynamic, and contingent (Ziman, 1978(Ziman, , 2002. Hence when Morgenthau is deeply critical of the Enlightenment idea that the use of human reason can be applied to the political realm, he most likely has in mind the positivist ideal of science, which partly helps explain, why, in Politics Among Nations he accepts a limited (non-positivist) account of science.
Morgenthau argued that the rationalist philosophy of the seventeenth and eighteenth centuries continued to make itself manifest in the period between the two world wars with devastating consequences. For Morgenthau (1946: 5), it could not be otherwise, as "the philosophy of rationalism has misunderstood the nature of man, the nature of the social world, and the nature of reason itself." As applied to the physical world, the rationalist view that "the world is governed by laws which are accessible to human reason" achieved some tremendous successes; the problem, however, was the belief that this same view could be extended to the social world. For Morgenthau, politics and the social world did not conform to the rationalist view, and the attempt to apply rationalism to human affairs inevitably led to disastrous consequences. The dire consequences of applying rationalism to politics were, according to Morgenthau, most evident in the triumph of liberalism on the international scene. Liberalism in international affairs, he argued, "is a rationalist ideology of foreign politics." This approach, Morgenthau (1946: 71) argued, "derives directly from the liberal misconception of international affairs as something essentially rational, where politics plays the role of a disease to be cured by means of reason." This is why, according to Morgenthau, rationalism leads to so much havoc on the international scene, as evidenced during the interwar period when it reigned supreme. Its problems are multiplied when it is applied to the world of politics. According to Morgenthau, while "politics must be understood through reason. . . it is not in reason that it finds its model." Most importantly for Morgenthau (1946: 10) is the claim that "politics is an art and not a science, and what is required for its mastery is not the rationality of the engineer but the wisdom and moral strength of the statesman." It seems clear that Morgenthau is invoking rationalism in its epistemological sense. Morgenthau means to invoke the Enlightenment idea that the use of human reason can be applied to the political realm in the same manner that science has applied it to the natural realm. However, the reasons for Morgenthau's rejection of rationalism are not epistemological, but ontological and political. The philosophy of rationalism, according to Morgenthau (1946: 5), "has misunderstood the nature of man, the nature of the social world, and the nature of reason itself." Rationalism fails for Morgenthau because it attempts to understand a world that is simply not susceptible to the kind of reason man can bring to bear on it.
Morgenthau, however, faces an additional problem. Having rejected the use of reason to study the realm of international politics in Scientific Man, how can he legitimate his own reflections on that realm in Politics Among Nations? Appeals to the "wisdom and moral strength of the statesman" are of little help in this regard, particularly when considered in light of some of Morgenthau's (1965) damning criticisms of those same statesmen. Morgenthau (1955: 16-19) confronts this problem head-on in Politics Among Nations and constructs a limited defense of a science of international relations. Hence, when taken together Scientific Man (SM) and Politics Among Nations (PAN) can be said to represent the difference between a strong (SM) and a weak (PAN) version of rationalism. Nonetheless, it is clear that by rationalism Morgenthau means only to signify any attempt to study a given realm of activity by the application of human reason to that realm; however contingent and incomplete the results of that study might be. Morgenthau's rationalism, then, does not require acceptance of the "rational actor" assumption.
A second major use of the term rationalism in IR comes from the work of Keohane (1988). While there are similarities between Keohane's usage and that of Morgenthau, there are clear differences. Keohane uses the term rationalism to group together those approaches that he sets in opposition to what he calls the reflectivist tradition. 3 Although Keohane recognizes the differences among the various rationalist approaches, he thinks there are elements that bind them together and which set them apart from reflectivist approaches. There are three aspects to Keohane's account of rationalism that are worthy of consideration. First, is the importance of what he (Keohane, 1988: 381) calls a substantive theory of rationality. Here he (Keohane, 1988: 381) draws on Herbert Simon, who argued that substantive rationality characterizes "behavior that can be adjudged objectively to be optimally adapted to the situation". As such, it is clear that a significant aspect of Keohane's use of the term rationalism is dependent on rational choice theory and by extension the "rational actor assumption" (Green and Shapiro, 1994). Rational choice theory uses a specific definition of "substantive rationality" to mean that individuals act "as if" balancing costs against benefits to arrive at outcomes that maximize personal advantage. In rational choice theory, all decisions, crazy or sane, are postulated as mimicking such a "rational" process. The "as if" is important in this formulation. Rational choice theorists do not actually have to believe that this is how individuals make decisions; they can, and often do, use this as an analytical device to help simplify the process of inquiry. This approach has been influential in economics and political science, and Waltz explicitly embedded his structural theory of international politics in microeconomic theory. As Williams (2005: 138) notes, "as has often been noted, despite its structuralist language, Waltzian neorealism was actually grounded in rationalist, microeconomic assumptions that place it clearly within the tradition of liberal rationalism, a foundation that provided a fertile basis for what Ole Weaver usefully dubbed the 'neo-neo synthesis'".
The second aspect to note about Keohane's concept of rationalism is that it is not dependent upon a materialist ontology. This runs counter to William's account of rationalism, which suggest that rationalist approaches are embedded within a materialist ontology. This might be the case with Waltz, but not with Keohane. In fact, Keohane's (1988: 382-386) definition of institutions is embedded in an ontology of rules, practices, perceptions, cognition, and cooperation, and these are clearly not exclusively materialist in form. Third, there is no necessary commitment in Keohane's treatment of rationalism to an empiricist epistemology, which again, is an essential feature of rationalism in Williams's account. Indeed, given his account of institutions, an empiricist epistemology will be wholly inadequate to deal with them; rules, perceptions, and cognition, are not directly available to the senses.
Confusion about the use of the term rationalism, however, became embedded within the discipline due to the way Keohane contrasted rationalist approaches with those approaches he labeled reflectivists. Keen to distance themselves from Keohane's "rationalists" the reflectivists began to use the label rationalism in a way that paid little attention to the specifics of the context in which the term was used. The reflectivist approaches that emerged in opposition to the mainstream from about the mid-1980s were objecting to a range of positions that were not always easily connected. However, once Keohane's concept of rationalism took hold, reflectivists began to use it in ways that went well beyond his original formulation, and the idea of a rationalist-reflectivist dividing line began to take hold. Yet, the discipline seems to have embraced this problematic distinction. Fearon and Wendt (2002: 54), for example, exemplify this view when they explain that rationalism as used in IR "seems to refer variously to formal and informal applications of rational choice theory to IR questions, to any work drawing on the tradition of microeconomic theory from Alfred Marshal to recent developments in evolutionary game theory, or most broadly to any 'positivist' exercise in explaining foreign policy by reference to goal-seeking behaviour." Brian Rathbun's work represents another recent attempt to grapple with rationalism in IR. By rationalism, Rathbun (2007: 541) refers "to the tradition in recent international scholarship that draws on microeconomic theories in which political actors seek to maximize their utility within structural constraints, most importantly a lack of information about intentions." This is consistent with Keohane's use of the term but not with that of Morgenthau and Williams, since Rathbun is clearly limiting his account of rationalism to the rational actor assumption and makes (at this point) no epistemological claims. Elsewhere Rathbun (2013: 2) argues that "rationalism is a distinct paradigm, an ontology of international relations painting a picture of utilitarian individuals acting strategically and instrumentally to further their own egoistic interests." He continues, "this is the ontology of game theory, bargaining theory, and the expected utility approach to foreign policy decision-making," all of which are correctly construed as adopting the "rational actor assumption." 4 The key terms for these theories are "preferences, information, strategies, and common knowledge" (Katzenstein et al., 1998: 678). All of these theories assume rational actors who engage in utilitarian calculations and pursue strategic interactions with other rational actors, but they make no assumptions about the importance of materialism, empiricism, or a commitment to some form of universalism.
It is clear that, for Rathbun, rationalism refers specifically to the "rational actor assumption." Yet, Rathbun (2008: 306) also claims that "neorealism is not a 'rationalist' paradigm." But if neorealism is not a rationalist paradigm, then according to Rathbun's own account of rationalism, it is not committed to the "rational actor assumption." This seems to be inconsistent with Rathbun's claim that for neorealism "states should judge and interpret their environment as objectively as possible, as mistakes can have serious consequences. The system provides incentives for rationality, understood as objectively understanding the implications of anarchy without illusions" (Rathbun, 2008: 305). This statement suggests that Rathbun believes that neorealism has a "rational actor assumption," even if the system provides the incentives for rational behavior. Often called "ecological rationality," systems of this kind require rational actors for their reproduction and are presented as an alternative to rational choice theory. However, the idea of ecological rationality already incorporates actor rationality and was a feature of Simon's (1957: 198, 202) original account of bounded rationality Simon. As Simon (1990: 7) would later put it, "Human rational behavior (and the rational behavior of all physical symbol systems) is shaped by a scissors whose two blades are the structure of task environments and the computational capabilities of the actor." We are now in a position to summarize the various confusing ways in which approaches that are said to be rationalist might differ. First, rationalism can be used in the way Morgenthau uses it; as a broad approach to the study of international politics that assumes the social realm is susceptible to the use of human reason in the hope of acquiring knowledge that can be used in achieving progress in human affairs. A second use of rationalism is that of rationalism as the "rational actor assumption"; that social life itself is composed of rational actors. Theories that accept the "rational actor assumption," and rational choice theory, can be understood as attempts to understand individual actors (which may be collectivities) as acting, or interacting, on the basis of the assumption that, given their objectives, resources, and circumstances, they are all attempting to do the best they can for themselves; they are acting rationally.
Many social scientists have constructed elaborate theories on the basis of this assumption. In rational choice theories, individuals are said to be motivated by the wants or goals that express their "preferences." They act within specific given constraints, and on the basis of the information that they have about the conditions under which they are acting. The relationship between preferences and constraints is treated in purely technical terms. It is a relationship of a means to an end. Since it is not possible for individuals to achieve all of the different things that they want, they must make choices about both their goals and the means for attaining these goals. Rational choice theories hold that individuals must anticipate the outcomes of alternative courses of action and calculate that which will be best for them. Rational individuals choose the alternative that is likely to give them the greatest satisfaction; often referred to as "utility maximization." Disaggregating these two approaches to rationalism helps illuminate the problems with those theorists that fail to distinguish between them.
Differentiating between these uses allows us to see that some forms of realism can embrace the "rational actor assumption" to varying degrees, yet not adopt "observer rationality." This, we believe, is the position adopted in Williams account of "wilfull realism." But equally some versions of realism can endorse "observer rationality" yet not accept the "rational actor assumption." Yet the discipline seems to assume that because the term "rational" appears in both rationalism and the "rational actor assumption" that these two positions are closely related. In some instances, they may be, but in many others they are not.

Rationalism and the rational actor assumption in realism
To ask if realism is a rationalist theory of international relations demands that we first understand in what sense rationality is claimed or denied. Textbooks typically claim that rationality is a core assumption of realism, but often neglect to specify what is meant by that claim. On the other hand, some realists deny that rationality is a core assumption of realism but fail to clarify what is it they are saying realism is not. The above discussion helps us clarify what is at stake here, but some examples will further illuminate the issue. Schweller (2003: 324), for example, does not identify rationality as one of realism's core assumptions. In fact, he argues that "realism's hardcore assumptions do not-contrary to conventional wisdom-include rationality." Jeffrey W. Taliaferro agrees that there has been a tendency to overstate the extent to which realist theories are rationalist. According to Taliaferro (2000Taliaferro ( /2001, "classical realism, neorealism, and neoclassical realism have an ambiguous and tenuous relationship to rational models of state behavior." And in their Introduction to Neoclassical Realism, the State, and Foreign Policy, Taliaferro, Lobell, and Ripsman concur with Schweller and Wohlforth, arguing that the rationality assumption is "not essential to realism" (Taliaferro et al., 2009: 22). And, as indicated at the beginning of this article, Mearsheimer (2009) has immersed himself into the controversy by claiming that Waltz intentionally decided to reject the "rational actor assumption" from his theory. According to Mearsheimer, Waltz "insists that his theory of international politics does not employ a rational actor assumption" (Mearsheimer, 2011: 425). 5 But which rationality assumption? That states, or state leaders, are rational actors (actor rationality)? Or rationalism understood in terms of a commitment to the possibility of a rational theory of international politics (observer rationality)?
Although we have established in the previous section that realist theory is not necessarily synonymous with all the meanings of rationalism as defined in the literature, in this section we aim to demonstrate that the "rational actor assumption" is a core assumption of almost all forms of realism. In fact, it is difficult to envision realist theory without the "rational actor assumption." More often than not, the "rational actor assumption" of realism implies nothing more than the idea that states behave in an instrumental manner to achieve their desired goals. Many realists do not devote a lot of attention to unpacking the "rational actor assumption" apart from asserting that states make considered assessments about their external environments and act strategically to realize their interests. As Grieco (1997: 164-165) explains "state rationality, from a realist viewpoint, has at least three elements." First, "realists assume that states are goal oriented." Second, "realists assume that states have consistent goals. . .state preferences are ordered and transitive in the sense that if outcome A is preferred to B, and B is preferred to C, then A is preferred to C." Third, "states are assumed by realists to devise strategies to achieve their goals" and "these strategies take into account the rank ordering by states of these goals." Likewise, Glaser (2010: 30) explains "acting rationally means that states are purposive actors that make at least reasonable efforts to choose the strategy that is best suited to achieving their goals. States are assumed to be able to identify and compare options, evaluating the prospects that they will succeed, as well as their costs and benefits." In these examples, the use of words such as "rationality" or "rationally" are references to the "rational actor assumption." Contrary to these who have recently argued that rationality is not a core tenet of realism, we aim to demonstrate that both realist and neorealist theory do indeed embrace the "rational actor assumption." But this should not be taken to mean that realism is synonymous with rationalism; at least not if rationalism, as is often the case, refers to something other than the "rational actor assumption."

Morgenthau and the "rational actor assumption"
It is impossible to summarize the complexity of Morgenthau's realism in a short section of an article. In part, this is because Morgenthau conflated the "rational actor assumption" and the possibility of "observer rationality." While noting the many obstacles that stood in the way of creating a theory of international politics, Morgenthau (1959: 20) wrote: What makes a theory of politics possible in spite of the ambiguities of its subject matter is the rationality in which both the mind of the observer and the object of observation, that is, politics, partake. Politics is engaged in by rational men who pursue certain rational interests with rational means.
Here, we can see the source of the confusion. For Morgenthau, what makes a theory of politics possible are two things. First, is the fact that the observer has a particular kind of rationality. Second, is the fact that politics is a practice conducted by rational men who pursue rational interests with rational means. Three things are worthy of note here. First, this rationality is common to both the observer and those engaged in the practice of international politics. Second, and keeping in mind his critique of rationalism in Scientific Man, it is reasonable to assume that Morgenthau thinks that if taken too far the rationality of the observer can lead to hubris and the scientism that he rejects. This is what Morgenthau means by rationalism. However, despite his critique of rationalism in Scientific Man, it is clear that Morgenthau also thought that a "rational" theory of politics was possible; hence our claim that in Politics Among Nations Morgenthau embraced a soft rationalism. Third, is the fact that Morgenthau must believe that both the "observer rationality assumption" and the "rational actor assumption" are universal characteristics. This must be the case since Morgenthau argues that all states act in a rational manner, and that rational observers can understand the strategic action of all states.
Indeed, if politics is "governed by objective laws that have their roots in human nature," then realism, Morgenthau (1955: 4) wrote, "must also believe in the possibility of developing a rational theory that reflects, however imperfectly and onesidedly, these objective laws." In the political sphere, the central concept for Morgenthau was interest defined in terms of power. This central concept, according to Morgenthau (1959: 17), "allows the observer to distinguish the field of politics from other social spheres, to orient himself in the maze of empirical phenomena which make up the field of politics, and to establish a measure of rational order within it." The concept of interest defined in terms of power served as the second of Morgenthau's six principles of realism. The concept, according to Morgenthau (1955: 5), enabled the political realist to navigate the landscape of international politics and "provides the link between reason trying to understand international politics and the facts to be understood." Moreover, it allowed Morgenthau to understand politics in terms of a Weberian ideal-type characterization (Turner and Mazur, 2009). It represented an ideal-type through which the theorist could understand reality. Moreover, the concept of interest defined in terms of power provided a rational map that could be used as a tool to approach political reality. It was rational for states to perceive their interests in terms of power, and the observer of that process could look over the shoulders of the statesmen and in some instances "understand his thoughts and actions perhaps better than he, the actor on the political scene, does himself" (Morgenthau, 1955: 5). Morgenthau embraces both the "rational actor assumption" and the belief that an observer could think rationally about the political realm. Morgenthau believed that this allowed him to provide "a kind of rational outline of politics, a map of the political scene." He wrote (Morgenthau, 1959: 17): Such a map does not provide a complete description of the political landscape as it is in a particular period of history. It rather provides the timeless features of its geography distinct from their ever-changing historic setting. Such a map, then, will tell us what are the rational possibilities for travel from one spot on the map to another, and which road is most likely to be taken by certain travelers under certain conditions. Thus it imparts a measure of rational order to the observing mind and, by doing so, establishes one of the conditions for successful action.
According to Morgenthau, not only does a realist theory of politics seek to depict the rational essence of politics, but normatively, a rational policy is also a good policy. Morgenthau was aware that the activity of politics contained both a rational and a contingent element. Indeed, it was the contingencies of politics-the accidents, the unforeseen and unanticipated events, the irrationalities-that proved to be the greatest obstacle to constructing a theory of politics. He believed that it was the task of theory to sort out the rational from the contingent elements so that a degree of order could be derived from the otherwise unconnected material. Thus, confirming his commitment to a soft form of rationalism. Theory can show that behind the seemingly random events of politics there are regularly repeated patterns of behavior such as the balance of power. Rationality was defended on the grounds that it provided the conditions of possibility for a theory of politics. Morgenthau (1955: 7) explained that political realism "shares with all social theory the need, for the sake of theoretical understanding, to stress the rational elements of political reality; for it is these rational elements that make reality intelligible for theory." On a second and more practical level, "political realism considers a rational foreign policy to be good foreign policy; for only a rational foreign policy minimizes risks and maximizes benefits and, hence, complies both with the moral precept of prudence and the political requirement of success" (Morgenthau, 1955: 7).

Structural realism and "rational actor assumption"
Most scholars would agree that realism is committed to the "observer rationality assumption." Waltz, in particular, sets out a detailed defense of the possibility of it in Theory of International Politics. In addition, in order to make the argument that the structure of the international system generates powerful incentives and disincentives for states to act in particular ways, it is necessary to assume that states are unified rational actors able to assess external constraints and opportunities and select appropriate policies on the basis of a cost-benefit analysis to pursue their national interest. If either individual decision makers are assumed to be non-rational, that is, plagued by cognitive pathologies, or states are disaggregated and unable to act coherently in a unitary rational manner, then it is impossible to postulate that structural factors can explain either the behavior of the component units or international outcomes. In short, it is reasonable to conclude that structural factors can only be incorporated in a general explanation of international politics if the actors are assumed to be rational. The source of that rationality may be considered to reside in the structural constraints, but unless the actors are also rational those structural constraints will not drive behavior in a manner that reproduces the logic of the system. In this manner, structural realism is committed to both the "rational actor assumption" and the "observer rationality assumption." Importantly, the "rational actor assumption" is what allows structural factors to be incorporated in a general explanation of international politics without reference to the idiosyncrasies of particular leaders or a range of domestic political variables. Without this, Waltz would be forced to accept reductionism. It is important, however, to distinguish between a theoretical assumption and how states act in the real world. Waltz (1979: 7) adopts an instrumentalist treatment of his theoretical assumptions, arguing that "in modeling a theory, one looks for suggestive ways of depicting the theory, and not the reality it deals with." He is categorical that the issue "is not whether the isolation of a realm is realistic, but whether it is useful. And usefulness is judged by the explanatory and predictive powers of the theory that may be fashioned" (Waltz, 1979: 8). In Waltz's account, rational actors are simply a theoretical assumption, and the fact that states frequently act in a non-rational manner is not a detriment to this theory. As he explains (Waltz, 1979: 91): In a micro theory, whether of international politics or economics, the motivation of the actors is assumed rather than realistically described. I assume that states seek to ensure their survival.
The assumption is a radical simplification made for the sake of constructing a theory. The question to ask of the assumption, as ever, is not whether it is true but whether it is the most sensible and useful one that can be made.
Recently, an opposing view has emerged that suggests that Waltz does not have a "rational actor assumption" in his theory. Mearsheimer (2009), for example, argues that Waltz deliberately eschewed the "rational actor assumption" and that scholars have failed to acknowledge the profound consequences this decision has for his theory. Likewise, Bessner and Guilhot have also argued that Waltz deliberately omitted the "rational actor assumption" from his structural theory. They claim (Bessner and Guilhot, 2015: 110) that "Theory of International Politics thus rested on methodological choices that excluded any 'rationality assumption' (i.e. the idea that humans were rational actors)." What are these methodological choices, and in what way do they exclude Waltz from embracing the rational actor model in Theory of International Politics? First, Bessner and Guilhot (2015) claim that Waltz says little about the roots of his theory. And second, they suggest having found a hidden ideological aversion in Waltz to decisionism embedded in cybernetics. However, both of these claims are subject to challenge. Waltz is clear on the micro-economic roots of his theory and cybernetics does not necessarily exclude decisionism. Bessner and Guilhot have confused Waltz's claim that theory itself is a creative exercise that comes in a flash of intuition and ignored his explicit claims about the roots of his theory. The distinction is between theory understood in a generic sense and Waltz's own specific theory of international politics. Waltz is very clear on the roots of his theory. His primary inspiration is economics. As Waltz (1979: 71) explains: How can one construct a theory of international politics without simultaneously constructing a theory of foreign policy? The question is exactly like asking how an economic theory of markets can be written in the absence of a theory of the firm. The answer is "very easily". Market theory is a structural theory showing how firms are pressed by market forces to do certain things in certain ways.
In fact, there are many instances where Waltz (1979Waltz ( , 1986Waltz ( , 2011 explicitly draws the analogy between his theory and that of the market. The "rational actor assumption" is most evident when we turn to Waltz's notion of an international system, which is built on the same underlying assumptions and principles of microeconomics. Keohane (1986: 167) recognized this connection when he wrote that "the Structural Realist research program is similar to that of microeconomics. Both use the rationality assumption to permit inferences about actor behavior to be made from system structure." The international system, according to Waltz, represents a distinct and separate level of analysis that helps to account for significant outcomes. Like the market in economics, the international system is an autonomous force that exerts pressure on the units that comprise the system. Waltz advocated what can be called a "top-down" approach proceeding from the international system to the individual nation-states. This is why he relied on a microeconomic theory of the market, not a theory of a firm. In this sense, Waltz embraces both system rationality and the "rational actor assumption." Waltz's explanation of the ordering principle of an anarchical international structure is also based on the analogy with microeconomic theory. He explains (Waltz, 1979: 91) that "international-political systems, like economic markets, are individualist in origin, spontaneously generated, and unintended." According to Waltz, it is through the interaction of the units that a structure emerges. The structure, in turn, helps to shape the behavior of the units. Here the analogy between microeconomics and international politics is particularly salient. Waltz (1979: 91) explains, "in both systems, structures are formed by the coaction of their units." The ordering principle of internationalpolitical systems is anarchy, meaning that it is a de-centralized realm of activity lacking an over-arching government. But notwithstanding the lack of an orderer, anarchy is a type of international order that does affect the behavior of the actors. According to Waltz, self-help is the key principle of action in both market and international-political systems. All of the actors must rely only on themselves to meet their objectives. In an anarchic structure, states, according to Waltz, are like units; they perform the same function. They are like units in the sense that each state is sovereign and seeks survival. As with microeconomics, the attributes of the actors are treated as theoretical assumptions to be used rather than variables to be explained. Waltz (1979: 91) assumes that a rational state will "seek to ensure survival" because "survival is a prerequisite to achieving any goals that states may have." This must also mean that he assumes that states rationally pursue their core interests in order to survive; if they did not rationally pursue their survival, the death rate of states would be considerably higher than it has been throughout history.
Waltz not only draws on microeconomics to help explain how the structure of the international system is generated, but he also borrows many of the same ontological assumptions that microeconomic theory makes about individuals and firms. Most fundamentally, microeconomics relies extensively on the assumption that actors, both individuals and firms, are rational. By analogy, the units of neorealism are self-interested and instrumentally rational sovereign states. Waltz explicitly endorses the assumption that states "are unitary actors who, at a minimum, seek their own preservation and, at a maximum, drive for universal domination." He assumes (Waltz, 1979: 118), moreover, that "states, or those who act for them, try in more of less sensible ways to use the means available in order to achieve the ends in view." Now to act in sensible ways is, we argue, is to behave in a rational manner. Commenting on a throwaway passage in his "A Response to My Critics" where he allegedly dismisses the word "rationality," Waltz (1986: 330) writes that he does not differ with Robert Keohane: over rationality, except semantically. I prefer to state the rationality assumption differently. My preference is based partly on fear that 'rationality' carries the wrong connotations. Since making foreign policy is such a complicated business, one cannot expect of political leaders the nicely calculated decisions that the word 'rationality' suggests. More significantly, my preference is based on the importance I accord, and Keohane denies, to the process of selection that takes place in competitive systems.
Here, Waltz is admitting that he has a "rational actor assumption," although he indicates that he prefers to define it differently from Keohane. His reluctance on using the term rationality, however, derives from his insistence that political leaders are rarely as rational and calculated as the theory suggests. But again, it has to be remembered, that for Waltz, theoretical assumptions do not have to be realistic. Hence the theory requires a rational actor, even if Waltz thinks actual actors are rarely rational.
Some who argue (Goddard and Nexon, 2005;Resende-Santos, 1996) that Waltz's theory does not have a "rational actor assumption" emphasize the role that he placed on socialization and the process of evolutionary selection to explain why certain patterns of behavior continually repeat themselves. The argument is that processes of selection, emulation, and socialization make the assumption of rationality unnecessary in accounting for international outcomes such as the balance of power. According to this interpretation, rather than assuming that states are necessarily rational actors, states emulate the successful actions of others and come to realize that the anarchical structure reward certain types of behavior and punishes other types of behavior. However, for Waltz, the dual mechanisms of socialization and emulation only make sense if it is assumed that states are rational actors. As he explains, "a market constrains the units that comprise it from taking certain actions and disposes them toward taking others." Likewise, "socialization encourages similarities of attributes and of behavior. So does competition. Competition generates an order, the units of which adjust their relations through their autonomous decisions and acts" (Waltz, 1979: 76).
The processes of socialization and competition provide strong support to our claim that Waltz does have a "rational actor assumption" in his theory. The competition that ensues in international anarchy has the effect of furthering the pressure on states to be rational. Waltz (1979: 76-77) writes that "competitive systems are regulated, so to speak, by the 'rationality' of the more successful competitors" and "competition spurs the actors to accommodate their ways to the socially most acceptable and successful practices." Thus, if structures have a socializing effect, and states seek to emulate the successful practices of other states, one must believe that states are rational actors who can comprehend their environment and engage in learning. State behavior has to be considered rationally matched to the rationality of outcomes the system demands.
The second significant influence on the development of Waltz's theory is systems theory, or more specifically, "cybernetics." According to Bessner and Guilhot (2015: 88), "Waltz incorporated cybernetics and system theory into Theory of International Politics, which allowed him to develop a theory of international relations that was no longer burdened with the problem of decisionmaking." However the conclusions Bessner and Guilhot draw from this are unfounded. Waltz (1979: 40, 56) admits that cybernetics was an influence in how he developed his theory, but its influence on him was not as strong as Bessner and Guilhot assume. As Waltz (1979: 59) explains: The presence of systemic effects, however, does not in itself mean that the realm of international politics can be defined as a system in the sense in which that term is used by general-systems theorists. In their sense, a system is a full-blown organization, hierarchically arranged with differentiated parts performing specified functions. The attempt to follow the general-systems model has been a misfortune, for our subject matter does not fit the model closely enough to make the model useful. International politics lacks the articulated order and the hierarchical arrangement that would make a general-systems approach appropriate.
Waltz rejects the applicability of cybernetics, or general-systems theory, to international politics for a specific reason. This is the issue of system "feedback" that he critiques in his discussion of Morton Kaplan's systemic theory. Waltz (1979: 56-57) notes how the concept of feedback is borrowed from cybernetics but claims that it has no purchase in international politics: By such as definition, feedback operates only within an organization; that is, the notion of feedback has no precise, distinct, technical meaning outside of a hierarchic order. . .But in international relations, what corresponded to such notions? Nothing! Kaplan simply uses the word without worrying about its formal appropriateness.
Although influenced by cybernetics and general-systems theory, Waltz explicitly rejects the idea that they have any applicability in terms of international relations.
Finally, Bessner and Guilhot (2015: 110) use a quote from Waltz to bolster their argument. As they put it, "Neorealist theory, Waltz wrote in the book [Theory of International Politics], requires no assumption of rationality or of constancy of will on the part of all the actors." Now importantly, it needs to be understood that Waltz chooses his words carefully, and he is saying is that neorealism requires no assumption on the part of "all" of the actors. But as he goes on to explain, the "theory says simply that if some do relatively well, others will emulate them or fall by the wayside. Obviously, the system won't work if all states lose interest in preserving themselves" (Waltz, 1979: 118). And which states will survive? Well, obviously those that act rationally in terms of the demands of the system. So, Waltz is correct, his theory does not need to assume that all states will act rationally, but for the system to survive some of them must act in a rational manner.
Mearsheimer is another theorist who has claimed that Waltz's neorealism has no "rational actor assumption." Mearsheimer's theory embraces the "observer rationality assumption." His theory of offensive realism unambiguously assumes that states act in a strategically rational manner to increase their prospects for survival. The assumption that great powers are rational actors is one of the five bedrock assumptions of offensive realism. Mearsheimer explains that great powers "are aware of their external environment and they think strategically about how to survive in it." Moreover, "they consider the preferences of other states and how their own behavior is likely to affect the behavior of those other states, and how the behavior of those states is likely to affect their own strategy for survival" (Mearsheimer, 2001: 31). By embracing the "rational actor assumption," Mearsheimer claims that his theory of offensive realism can explain both important international outcomes, such as the formation of balancing coalitions and the conditions that lead to great power war, and the foreign policies of the great powers. Because of the "rational actor assumption," he expects that most of the time, states will act according to the logic of offensive realism. International politics, according to Mearsheimer, is one of perpetual competition with the great powers struggling against each other to achieve a dominant position.
By including the "rational actor assumption" in his theory, Mearsheimer believes his structural theory provides a more accurate description of international politics than what Waltz, and other defensive realists, can offer. 6 Moreover, unlike Waltz, Mearsheimer believes his theory can explain both international outcomes and foreign policy. Waltz (1996), of course, does not believe that his theory can explain foreign policy. For Mearsheimer, Waltz, and defensive realists more broadly, need a separate theory of domestic politics to explain foreign policy behavior. It is worth pointing out, however, that while Mearsheimer believes that the "rational actor assumption" allows him to explain much of the behavior of the great powers over the millennia, examples of nonstrategic state behavior-such as the United States decision to invade Iraq in 2004count against his theory that states act rationally.
In other words, examples of non-rational state behavior are as much a problem for Mearsheimer's offensive realism as they are for many forms of realism. On the other hand, non-rational state behavior is not a problem for Waltz's theory for two reasons. First, because he maintains that he is not explaining state behavior, only international outcomes. Second, because he does not treat his theoretical assumptions realistically but only instrumentally. Waltz does not accept that when states fail to act as predicted by the theory that this is a falsification of the theory. Again, as he (Waltz 1979: 119) explains when discussing Organski's critique of balance of power theory: His [Organski's] basic error lies in misunderstanding what an assumption is. From previous discussion, we know that assumptions are neither true nor false and that they are essential for the construction of a theory. We can freely admit that states are in fact not unitary, purposive actors. . .But all of this has always been known, and it tells us nothing about the merits of balance-of-power theory.
The fundamental issue here is the important distinction between "in fact," and "in theory." Why does Mearsheimer believe that Waltz does not have a rational actor assumption in his theory? Mearsheimer argues that Waltz's theory of international politics is actually composed of two parts. The first part, what Mearsheimer terms the "Waltzian baseline," is the most familiar; it rests on the dual assumptions that states are the main actors in the anarchic international system, and that their primary motive is to survive as a sovereign entity. This baseline aspect of theory, according to Mearsheimer (2009: 246), allows Waltz to explain "how states would act if they were rational agents." For Waltz, if states behaved in a rational manner, there would be less war because states would pursue a more restrained foreign policy. Mearsheimer (2009: 244) writes, "in effect, Waltz is saying that there would be little conflict in the international system if great powers acted strategically almost all of the time." He argues that if rational states are included in the Waltzian baseline, then international politics would, for all intents and purposes, be relatively tranquil and benign. 7 Rational states would recognize that attempts to augment their power are almost always counter-productive because other states will engage in balancing power.
According to Mearsheimer, however, Waltz does not believe that states always act in a rational, strategic manner to advance their own best interests; they start unnecessary wars and aggressively seek to augment their capabilities through conquest. Waltz acknowledges that history confirms the point that states often act foolishly and contrary to what reason would dictate. This is why, according to Mearsheimer, Waltz and other defensive realists need a separate domestic theory of foreign policy to explain all the cases when states fail to act in a strategic and rational manner. A separate theory of foreign policy is needed "because domestic politics intrude into the policy-making process and trump sound strategic logic" (Mearsheimer, 2009: 245). But this does not mean that Waltz has no "rational actor assumption." Mearsheimer's error is to treat Waltz's admission that states often act in irrational ways as evidence that Waltz did not believe that some states acted rationally most of the time. Waltz knew only too well that states often acted irrationally, but this is a claim about the practice of states in the world, not in the theory. Waltz's theory needs the assumption of actor rationality, for without it he has no means to identify, or predict, what the appropriate action would be within a given system structure.
In his attempt to refute that Waltz has a "rational actor assumption," Mearsheimer comes close to misrepresenting structural realism theory. As Rathbun (2008) makes clear, neorealism is a theory of constraints and incentives; not a determinative theory of state behavior. As Waltz himself acknowledges, states can behave in any way they chose, but the structure that they operate in will reward certain behaviors and punish others. Waltz (2003: 53) explains that states are free to "do any fool thing they care to, but they are likely to be rewarded for behavior that is responsive to structural pressures and punished for behavior that is not." This, we submit, means that Waltz does embrace the "rational actor assumption." Waltz (1986: 331) writes: That some states imitate the successful practices of others indicates that the international arena is a competitive one in which the less skillful must expect to pay the price of their ineptitude. The situation provides enough incentive to cause most of the actors to behave sensibly. Actors become "sensitive to costs" to use Shai Feldman's apt phrase, which for convenience can be called an assumption of rationality. This is a very significant quote that directly refutes the claim that Waltz does not accept the "rational actor assumption." Moreover, Waltz's commitment to the "rational actor assumption" is clear when one considers his discussion of the properties of the units in his theory. As he (Waltz, 1979: 96) explains: to say that a state is sovereign means that it decides for itself how it will cope with its internal and external problems, including whether or not to seek assistance from others and in doing so to limit its freedom by making commitments to them. States develop their own strategies, chart their own courses, make their own decisions about how to meet whatever needs they experience and whatever desires they develop. This is about as clear account of a rational actor as one could wish for. But, additionally, Waltz needs the "rational actor assumption" in order to demonstrate what the correct course of action would be in the structural conditions he identifies. Without this, he has no way of saying whether any behavior is either in accordance with the dictates of the structure or is not. States seek to survive, and the only rational behavior is that orientated toward this end, which is why Waltz is committed to the "rational actor assumption."

Realism as a normative theory
In many ways, the "rational actor assumption" serves as a normative ideal for realist theoreticians. If only states could act in a consistently rational manner international politics would be a less tragic activity. At the same time, the "rational actor assumption" is often belied by the practice of international politics. For Waltz, this does not represent a major anomaly because his instrumentalist notion of theory considers rational actors to be a useful assumption that is not undermined by examples of non-rational behavior. Conversely, non-rational behavior does represent a major anomaly for offensive realism because Mearsheimer's notion of theory considers assumptions to be realistic regardless of their difficulty of being realized in practice. Irrespective of what constitutes a theoretical anomaly, we argue that the rational actor assumption of realism serves as a normative ideal. This is not an original argument. Trachtenberg (2012: 43) has thoughtfully argued that realism is a theory of peace, not war. According to Trachtenberg, foreign policies that are rational in power-political terms actually contribute to a more peaceful world. Most realists do, however, dismiss the idea of perpetual peace and instead opt for international stability. Nomenclature aside, the point here is that many realists believe that if states acted rationally there would be less war and instability in the world.
Before briefly turning to Morgenthau, Waltz, and Mearsheimer, it is important to acknowledge Glaser's attempt to create a prescriptive, normative theory of realism. Contrary to other structural realists, Glaser does not believe that the condition of anarchy inevitably gives rise to a Hobbesian world of competitive power seeking behavior. In fact he shows that, similar to Waltz, endlessly seeking greater gains in power often has suboptimal results and unfortunate consequences. To correct this misinformed view of state behavior, Glaser develops a normative theory of how states should ideally behave. Fundamental to his theory is the assumption that states make rational decisions, which he argues "is necessary for a prescriptive, normative theory" (Glaser 2010: 30). At the same time that Glaser's rational theory prescribes how states should act to achieve their strategic objectives, he is fully cognizant of the fact that history provides countless examples of states failing to act in a rational manner. In many ways the agenda of neoclassical realists has been to fill the gap between expected and actual behavior, which is why some refer to neoclassical realism as a "theory of mistakes" (Rathbun, 2008). But where many neoclassical realists go wrong is the mistaken belief that "both Waltz and Morgenthau reject the assumption that states act rationally" (Taliaferro et al., 2009: 22).
As we discussed above, Morgenthau's theory relied extensively on the rational actor assumption. He postulated that the assumption of rationality was a necessary precondition of creating a theory of international politics. Not only was rationality a distinguishing attribute of his realist theory, but it was also the basis on which he critiqued American foreign policy. Morgenthau's sage advice over his long career was meant to steer American foreign policy makers in a more rational direction so as to minimize the need to use military force and reduce the danger of using nuclear weapons. Political realism, for Morgenthau (1955: 7), "considers a rational foreign policy to be a good foreign policy; for only a rational foreign policy minimizes risks and maximizes benefits and, hence, complies both with the moral precept of prudence and the political requirement of success." The fact that states often failed to live up to the ideal of rational behavior was not, according to Morgenthau, a fault of the theory. To assume that examples of irrational behavior invalidated realism is to misconstrue his project of developing a theory of international politics. Morgenthau's (1955: 8) intention was "to present not an indiscriminate description of political reality, but a rational theory of international politics." The normative dimension of the rational actor assumption is in full display when Morgenthau turned his attention at the end of Politics Among Nations to the rules of diplomacy, which he regarded to be the best means of preserving peace. Above all, Morgenthau's prescription was for policymakers to follow the national interest in a rational manner. Like Morgenthau, Waltz was also committed to reducing violent conflict among nations. Waltz believed that the world would be a better place-less violence, less militarism, more cooperation, and greater self-restraint-if only state actors behaved in a consistently rational manner. Rational states would be able to follow the demands and incentives of the structure of the international system. They would be able to recognize the constraints and incentives of the international system and devise appropriate policies. What structural realists argue (Trachtenberg, 2012: 7) is "that systemic forces can actually play a positive role-and indeed that systemic pressures by and large have a stabilizing effect." This is dependent, however, on states behaving rationally. Rational policies, structural realists argue, are one's that place a premium on self-restraint and moderation. This is one of the reasons why Waltz never became a unipolar optimist. He feared correctly that without a bipolar structure, American foreign policy makers would not be able to restrain themselves because "countries that wield overwhelming power will be tempted to misuse it" (Waltz, 1993: 189). Finally, the best way to understand Waltz's prescriptive views regarding nuclear proliferation is to recognize how deeply he believed in the concept of rationality. Unlike those who oppose Iran becoming a nuclear state on the grounds that the regime is inherently non-rational, Waltz argued "Iranian policy is not made by 'mad mullahs' but by perfectly sane ayatollahs who want to survive just like any other leaders" (Waltz, 2012: 4). In this regard, structural realism is both a descriptive explanatory theory and a prescriptive normative theory. Mearsheimer (2009: 253) recognizes the normative dimension of Waltz's theory when he writes that his theory "is best suited to serve as a set of prescriptions for how states should behave so as to maximize their prospects for survival." But as we showed above, Mearsheimer mistakenly believes Waltz does not have a rational actor assumption. Mearsheimer's theory of offensive realism does have a rational actor assumption and he argues that it makes logical sense for states to continuously pursue more power even through the means of war. However, and despite the contradictions between his descriptions and prescriptions, he normatively values peace over war. Not only is it well-known that Mearsheimer was one of the most vocal critics of the Iraq War (Mearsheimer and Walt, 2003), but he also opposed the war on terror and the invasion of Afghanistan. He actually called for a "hearts and minds" strategy, rather than the violent pursuit of empire, to deal with Islamic hostility following the 9/11 attacks (Mearsheimer, 2002). And as early as 2015, he was opposed to arming Ukraine on the grounds that this would provoke Russia (Mearsheimer, 2015). Not only do these examples further validate our argument that realism is a normative theory, but the reason that Mearsheimer provides for why the United States fails to abide by the dictates of realism is the inability to act in a rational manner. If American foreign policymakers acted on the basis of rationality, instead of choosing war and violence, they would select better options such as containment, hearts and minds strategies, and respect for other countries spheres of influence. In this regard, even Mearsheimer's theory of offensive realism is, in a way, a normative, prescriptive theory of how states should act.

Conclusion
We have attempted in this article to sort through the considerable confusion that exists about the meaning of Rationalism in the field of IR. We have deemed it necessary to differentiate between rationalism, rationality, and the "rational actor assumption." This was a necessary step in order to demonstrate that realist theory is beholden to the "rational actor assumption." It is clearly apparent that some of the confusion about realism's relationship with rationalism is a function of how this word has been used in the literature. By disaggregating the various meanings, we were able to concentrate on the question of whether or not the "rational actor assumption" is a necessary component of realist theory. We found that despite claims to the contrary, realist theory-both the realism of Morgenthau and the structural realism of Waltz and Mearsheimer-embraces the "rational actor assumption." In addition, distinguishing between the "rational actor assumption" and the "observer rationality assumption" disrupts the idea of rationalism as a description of a broad range of theoretical approaches. The category of rationalist IR theory obscures more than it illuminates. Unpacking this distinction opens up space for a more considered assessment of the differences between theoretical traditions, as well as hopefully providing pathways for increased theoretical dialogue. Rather than treating Rationalist IR theory as one monolithic bloc the subtle, but important, differences between forms of Rationalist theorizing can help approaches once deemed to be on opposite ends of the theoretical spectrum to see what they share, or do not share, in common.
Finally, a detailed consideration of the role of the "rational actor assumption" in realist theory demonstrates that this is not an objective description of how states do behave, but a normative account of how they ought to behave. As such the historical claims of realism to describe the world as it is, can no longer be taken for granted. Much of the empirical evidence suggests that states do not always act rationally. It certainly has been the case historically that that the policy prescriptions of realists have not always coincided with the empirical conditions of international politics. There is, in other words, a gap between the theory and the practice. But what realists have attempted to do is to show how a rational foreign policy, especially on the part of the United States, can lead to a more restrained and less violent grand strategy. When realists prescribe a grand strategy of offshore balancing, or restraint, it is not simply a strategic argument; it is also a normative, value-based recommendation (Layne, 2006: 202-205). This distinction between the actor rationality assumed by the theory and the irrationality of state behavior, provides a compelling reason to think that Morgenthau was on to something when he raised the possibility of a counter-theory of irrational politics (Morgenthau, 1993: 7).