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date: 20 September 2017

Opportunity and Willingness: From “Ordering Concepts” to an Analytical Perspective for the Study of Politics

Summary and Keywords

The opportunity/willingness framework (O/W) is presented as an agent-structure approach to the understanding of international relations (IR) and international conflict, with deep roots in the “ecological triad” of Harold and Margaret Sprout. While originally developed to organize thinking about international politics, this article describes how it has evolved into a guide for generating IR theory, developing research designs to study IR, and ways to evaluate those theories. It does this by showing how to synthesize what we know and bring together apparently disparate hypotheses and evidence to bear—crossing a variety of analytic boundaries—and by pulling together what we know across levels of analysis, academic disciplines, and the sub-disciplines of political science. O/W compels scholars to cross, link, and synthesize levels of analysis—complementing theories built around levels of analysis, while at the same time moving them forward in order to deal with the complex causation they have to confront. This complex causation derives from the logical features of O/W, which regards opportunity and willingness as jointly necessary conditions for the occurrence of any event. A discussion of the characteristics of necessity and sufficiency as causal processes leads to the conclusion that not only does this joint necessity distinguish O/W from theoretical approaches that are deterministic, monocausal, or are concerned only with either opportunity or willingness, but is the beginning of a logical story that demonstrates how this framework can deal with causal complexity. The joint necessity of opportunity and willingness, along with its two corollaries of “substitutability” and “nice laws,” forces a researcher to more fully specify the logical and substantive structure of the theoretical statements under investigation, and to ensure the research design is relevant to the theory and set of research hypotheses—such that there is a coherent relationship among the components of logic, theory, and method. At the end of the logical story developed in the article, it can be seen that O/W has moved well beyond an organizing principle and is a model of causal complexity of great potential.

Keywords: agent-structure approach, opportunity, willingness, environment, substitutability, nice laws, causal complexity, logic, necessity, equifinality, empirical international relations theory


The opportunity and willingness framework (O/W) was first presented in Starr’s 1978 article and subsequently elaborated in Benjamin Most and Harvey Starr, Inquiry, Logic and International Politics (1989). O/W is an agent-structure approach to the understanding of international relations and international conflict. It was also seen as a guide to developing research designs for their study. O/W was initially developed to organize thinking about international politics. Opportunity and willingness were seen as ordering concepts that could synthesize the apparently unrelated results of different disciplines, as well as cover and improve on the use of levels of analysis (as in Waltz’s three images of international conflict [1959]).

O/W draws upon the “ecological triad” of Harold and Margaret Sprout, which is comprised of an entity, its environment, and the entity-environment relationship. O/W was originally developed as a framework ultimately concerned with the possibilities and constraints that face decision-makers (opportunity) and with the choices they make in light of these possibilities and constraints (willingness). An important argument that has become more fully specified across time (from Starr, 1978; to Most & Starr, 1989; to Cioffi-Revilla & Starr, 1995; to Friedman & Starr, 1997) is that opportunity and willingness are jointly necessary conditions for the occurrence of behavioral phenomena. Within the international relations literature, this insistence that both entity and environment be studied through interactive, adaptive feedback loops has stood out against approaches (such as structural realism) that look only at characteristics of the international system or look only at the decision-maker (as found in some formal game approaches, historical/biographical approaches, or some social-psychological approaches).

As an agent-structure approach, O/W naturally leads the researcher into process-oriented conceptualizations of international relations. It does so by employing the Sproutian argument for abandoning deterministic models, by requiring the investigation of decision-making processes (and models), and by requiring that events must be seen as the joint interdependent outcomes of two or more states (or any set of international actors). Regarding research design, O/W requires developing and utilizing logical analyses based on necessity and sufficiency—including their meanings and interrelationships. Thus, as with any agent-structure approach, the use of O/W reveals the complexity and uncertainty of international phenomena: a complexity not adequately addressed by realism, neo-realism, or most variants of transnational liberalism. Yet, as Cioffi-Revilla and Starr (1995, p. 468) demonstrate, “the fundamental uncertainty of politics is scientifically tractable.” Starr and colleagues have argued that with concepts such as substitutability, nice laws, context, and adaptation, O/W can deal with both the analytical and operational levels of theory and give scholars a better grasp of what behaviors are more or less likely to occur under what conditions.

The editor of this encyclopedia, William Thompson, has expressed to contributors his concern with two formidable problems found in empirical international relations theory. One is that “our analytical cultures tend to discourage specific attention to the structure of the theoretical argument,” while “[a] second problem is that our theoretical testing approaches tend to be fragmented and not always cumulative.” It should be noted that both problems were central to the work of Most and Starr (1989) on the logic of inquiry and the reciprocal relationships between theory and research design (as well as the set of feedback loops among the components of research design itself). Given that O/W was a major part of the foundational structure of Most and Starr’s logic of inquiry, it also means that O/W can be usefully employed to address both of the problems raised by Thompson.

Many volumes and thousands of pages have been devoted to exactly what theory is and the various forms it may take. My career-long approach to theory is that it is a necessary handmaiden to the enterprise of empirical research. This approach is neatly summarized by Dougherty and Pfaltzgraff (1981, pp. 11–12) who note that theory is an “intellectual tool … that helps to organize our knowledge, to ask significant questions, to guide research.” How theory does this is also summarized by Russett and Starr (1996, p. 30) noting that “theory organizes and simplifies reality; thus helping to separate the important from the trivial by pointing out what we really wish to look at and what is unimportant enough to ignore. This is why theory is important.” O/W is not a causal theory of the sort found in, say, formal theoretical presentations. However, as we will see in a brief overview of the evolution of O/W, whether O/W is seen as broad perspective, a framework, or a pre-theory, it fulfills the tasks of theory as an intellectual tool and guide. It is also clearly a theoretical approach to causal theory, which is based on the causal logic of necessity (only if X then Y), if not the more familiar causal logic of sufficiency (if X then Y).

The next section reviews the nature of agent-structure models, with particular attention to the ecological triad of Harold and Margaret Sprout. This is followed by the structure and components of O/W itself, as summarized by the “menu” metaphor. A section on the evolution and development of O/W follows, including such corollaries as substitutability, nice laws, and other contributions of O/W. A review of the overall importance of O/W to the study of IR leads to an explicit discussion of how it helps to address the two key problems raised by this volume’s editor.

From Agent-Structure Approaches to O/W

As noted, O/W can be seen as it relates to the broader debate in the literature concerning the agent-structure relationship (see especially Friedman & Starr, 1997). Agency and structure are the defining components of society. The agent-structure problem refers to questions concerning the interrelationship of agency and structure (i.e., to the human agents situated within some set of institutional structures or the structure of the set of environments within which those humans act). Agent-structure approaches have to deal with how agency and structure affect each other, and how these relationships can help explain social phenomena. The agent-structure problem raises a variety of issues in the philosophy of science and the logic of inquiry (see Most & Starr, 1989, 2015).

Most simply put for students of international relations, agent-structure approaches focus on the behavior of foreign policy decision-makers within varying contexts and environments. It should be noted that concern with the recursive and dialectical interrelationship between multidimensional and dynamic sociopolitical contexts and the choice processes of individual decision-makers, policymakers, or what Friedman and Starr term “international political elites,” is a prominent feature of agent-structures approaches such as O/W.1 O/W is not unique; there are other agent-structure models. However, O/W owes its greatest intellectual debt to the work of Harold and Margaret Sprout.

Friedman and Starr (1997) consider the Sprouts as leading the first generation of international politics agent-structure theorists. The works of Harold and Margaret Sprout (1956, 1968, 1969), especially as refined and applied by Starr (1978) and Most and Starr (1989), have been used explicitly to address the agent-structure problem. The Sprouts’ (1968, pp. 11–21; 1956, pp. 17–19; 1969, p. 42) notion of the “ecological triad” (i.e., entity, its environment, and entity-environment relationships) addresses the relationship between agency and structure. As a reaction to the determinism of the late 19th- and early 20th-century approach to geopolitics, the Sprouts developed a set of alternative ways to view the components of the ecological triad, especially the relationship between entity and environment. It is important to note that these alternatives were developed “as alternatives to environmental determinism, where, by definition, decision makers are incapable of choice given the characteristics of the environment, or ‘milieu’” (Sprout & Sprout, 1969, p. 44).

The Sprouts provide three useful alternative ways to address the ecological triad: environmental possibilism, cognitive behaviorism, and environmental probabilism. Environmental possibilism refers to structure and is defined as “a number of factors which limit human opportunities, which constrain the type of action that can be taken as well as the consequences of that action” (Most & Starr, 1989, p. 27). Cognitive behaviorism represents “the simple and familiar principle that a person reacts to his milieu as he apperceives it—that is, as he perceives and interprets it in light of past experience” (Sprout & Sprout as cited in Most & Starr, 1989, p. 28). Environmental probabilism is a third way to look at the entity-environment relationship. It represents both the core concept of uncertainty in political behavior (see Cioffi-Revilla & Starr, 1995, p. 451) and what may be viewed as a synthesis of these first two relationships. Environmental probabilism refers to “explanation or prediction by means of a generalized model, of the average or typical person’s reaction to a given milieu” (Sprout & Sprout, 1956, p. 50). In other words, the attributes of an agent’s environment “provide cues as to the probability of certain outcomes” (Most & Starr, 1989, pp. 27, 29).

Most and Starr’s (1989, pp. 27, 29) discussion of the virtues of the ecological triad can itself be viewed as a statement of the agent-structure problem:

The advantages of this framework … derive from its applicability to any number of levels of analysis. That is … the concept of the ecological triad argues that we need to look at the ongoing policy/choice processes within that entity [the unit of analysis], its context or environment, and then the interaction between the entity and the environment … It should be clear that the ecological triad calls for the study of both entity and environment, and most importantly, how the two are related. The ultimate entities—single decision makers or small groups of decision makers—are surrounded by factors that structure the nature of the decision, the options available, the consequences, costs, and benefits of those options. Individuals, then, make choices within a complex set of incentive structures. This can be captured only by looking at all three parts of the ecological triad.

Opportunity, Willingness, and the Menu for Choice

O/W as developed in Starr (1978) and Most and Starr (1989) represents a reformulation of the Sproutian discussion of the agent-structure problem. Opportunity, based on environmental possibilism, refers primarily to the “possibility of interaction.” Opportunity means that “conditions exist that permit sufficient interaction between states, that adequate capabilities and resources exist to allow certain kind of action to take place, and that decision makers perceive both the range of possible interactions and the extent of capabilities” (Russett & Starr, 1981, p. 23). In other words, “it closely parallels the idea that what humans do is constrained by the actual possibilities in the ‘objective’ environment.” Important sources of possibility include geopolitical factors such as proximity and borders (see, e.g., Starr & Most, 1976; Most & Starr, 1980; Starr, 2013), as well as the various means by which humans manipulate this environment—especially technology (see also Most & Starr, 1989, pp. 30–31; Starr, 2013).

Opportunity, following environmental possibilism, thus also refers to “the existence of capabilities that permit the creation of opportunities … Capabilities, then, not only may promote, but actually permit interaction” (Most & Starr, 1989, p. 30). There are two related but distinct ways to look at levels of capabilities and possibilities. First, as Most and Starr (1989, p. 31) note, “some capability—technology, ideology or religion, form of government, manner of organizing people to some task, etc.—must be created/invented so as to be part of the range of possibilities available to at least some members of the international system.” The second level involves how the various capabilities or factors in the environment are distributed among states or other international actors. In sum, they note (1989, p. 32): “At one level all international actors share the same menu of possibilities—no one could have nuclear weapons to fight World War I because they had not yet been invented … At another level international actors may have very different menus of possibilities—the wealth, technological talent, and resources needed to take advantage of the nuclear possibility are not evenly distributed.”

Willingness, closely related to cognitive behaviorism, refers to “the choice (and process of choice) that is related to the selection of some behavioral option from a range of alternatives. Willingness thus refers to the willingness to choose (even if the choice is no action), and to employ available capabilities to further some policy option over others” (Most & Starr, 1989, p. 23). That is to say that willingness deals with the motivations of people (Friedman and Starr’s foreign policy decision-making elites) to take advantage of opportunities. Willingness deals with perceptions, emotions (e.g., fear, insecurity, revenge), and all of the factors related to the choice within the set of perceived available alternatives.

Thus, the original O/W construct/framework/pre-theory directed the attention of scholars to the possibilities and constraints that face decision-makers (O) and with the choices that they make given those same possibilities and constraints (W). As noted above, O/W as an agent-structure approach cuts across levels of analysis and forces the scholar to interweave them—as O/W is concerned with the relationships that nest decision-makers within their surrounding environments. Given that a large amount of writing on IR theory is organized around levels of analysis—note that even the Russett and Starr textbook (through the first six editions) uses levels as one major organizing principle—O/W is both a useful complement to theories built around levels of analysis and at the same time moves them forward in order to deal with the complex causation they have to confront (e.g., see Most & Starr, 2015, preface). Starr (2002, p. 55) summarizes O/W and its synergy using the levels of analysis employed in the Russett and Starr textbook (italicized below for the purposes of this article):

This approach holds that the study of politics involves the study of individual agents making choices under specified conditions and within specified structural contexts. The willingness of the decision maker to make certain choices is constrained by that individual’s own nature, as well as by the decision maker’s place in the governmental structure (or, role); the nature and form of the government within which the decision maker operates; the resources, makeup, and politics of the society that houses the decision maker and the government; the web of influence relations that the decision maker’s state has with other world actors; and the structure of the world system … Each of these levels of analysis affects the opportunities available to decision makers; each level affects the images decision makers hold and how they make choices.

Work by Starr and colleagues demonstrate that these two (initially) pre-theoretic concepts can serve as organizing concepts for the IR literature. In other words, Starr has shown that the various explanations of international conflict, for example, can be synthesized and that they can be categorized according to opportunity and willingness. This point is crucial to the current discussion because it highlights the notion that all independent variables explaining social phenomena can be characterized as either agentic or structural variables (see Friedman & Starr, especially chaps. 4 and 5). In this way, it has been argued that O/W allows the scholar to see the commonalities across disparate literatures and to “cross boundaries” that separate disciplines and sub-disciplines, basic and applied research, and various methodologies and/or epistemologies.2

The interrelationship between agency and structure may be most easily conveyed in the terms of Russett’s “menu” metaphor (Russett, 1972, pp. 112–113; see also Russett & Starr, 1996, pp. 22–23). Any menu “provides a number of behavioral/choice possibilities, not determining the diner’s choice, but limiting it” (Most & Starr, 1989, p. 28). Initially, the agent must be able to “read” the menu (cognitive behaviorism). This also reflects the Sprouts’ insistence that agents must be aware of the possibilities made available by the environment. The menu presents such possibilities to the agent (environmental possibilism). Willingness involves the factors based on the agent: values and preferences along with resources. In the restaurant, these factors convert into what types of food a diner likes and dislikes (likes Italian, other cuisines not so much), as well as specific dishes (loves pizza, but is not so fond of calamari). A diner’s (agent’s) resources may be represented by the amount the diner can spend or wants to spend. The menu also represents the structure or environment. The prices listed, size of portions, or the reputation for certain dishes, etc., will make certain choices more or less likely (environmental probabilism). The menu metaphor thus conveys the anti-determinism that motivated the Sprouts, combining their three main alternatives as it mirrors the O/W framework.

Most and Starr (1989) and Cioffi-Revilla and Starr (1995) demonstrate how opportunities (the menu) can create or influence the incentive structures for willingness (the food orders actually chosen). Indeed, a common theme in the works of Starr and colleagues is how opportunity can generate greater levels of willingness, but they also treat how willingness can lead to different levels of opportunity. The latter idea reflects the notion that an agent can ask for something that is not on the menu! By so doing, the agent may also change the menu itself. As noted in Siverson and Starr (1991) and Starr (1991), for example, technological innovation both changes the meaning of the geopolitical context (see Goertz, 1995; Starr, 2013), as well as the available set of environmental possibilities. Similarly, all human innovation, including the creation of new ideas, ideologies, modes of organization or production, etc., changes the “menu.” Many of these changes are unintended, but others, such as weapons development, are clearly aimed at revising environmental possibilities. The menu is thus useful for thinking about the required relationship between opportunity and willingness: The diner cannot get a meal unless she is in the restaurant (the restaurant does not do takeout), is able to read the menu and see the choices, is willing to choose a dish, and has the ability to pay for it. As noted, a fundamental premise—and advantage—of O/W is that “both the environmental/structural level and the decision-making/choice level are required for a full description and explanation of international relations phenomena” (Most & Starr, 1989, p. 23). This is not to assume or assert that opportunity and willingness are equally weighted across all situations. Indeed, in Starr (1978), an initial depiction of how opportunity and willingness might relate to one another, as well as to the occurrence of some action, included the requirement that both opportunity and willingness had to have crossed some threshold. The shape of this threshold was not presented as a given, nor was it argued that one factor was always (or more often) important than the other. The notion of having a threshold for either to be present is key to the issues of necessity discussed later.

As noted, there are situations when one part of O/W may move the other across some threshold. As theory drives the analyst’s question, and the question drives the research design, the importance of opportunity and willingness to each other depends on both the specific question and design. For example, opportunity as “system structure” or “polarity” generally changes slowly, or presents an analyst with few cases. Most and Starr (1989) deal with this through the use of simulations and conclude that small changes in willingness may be more important in regard to international conflict than elements of the system structure (e.g., number of states and number of major powers). Thus, for many studies, willingness is more dynamic and variable, changing more often and/or quickly with changes in personnel, technology, or other human inventions (see also Friedman & Starr, 1997). However, technology may also add dynamism to opportunity. As is noted, the question of how opportunity and willingness relate to each other is still open, and the weighting of each will fluctuate from study to study.3

The pre-theoretic hypothesis that both opportunity and willingness are required might itself be viewed as a statement of the agent-structure problem, and as such it represents a central prescription for theories of international politics. But O/W has moved from its initial pre-theoretical state as Starr and his collaborators have additionally derived significant methodological, theoretical, and meta-theoretical implications from this agent-structure hypothesis: Both opportunity and willingness are necessary conditions for any action to take place.

As stressed in Most and Starr (1989), all of the interactions that IR scholars study are the joint outcomes of two or more actors—each of which is required to have both the opportunity to act and the willingness to act. Most and Starr (1989), for example, using war as the main illustration for their arguments, are then able present a conceptualization of international political outcomes (such as war) as the spatiotemporal intersection of agency choice.

Evolution of O/W: Joint Necessity, Substitutability, and Logic of Inquiry

It has been argued that O/W promotes crossing boundaries between epistemologies and models of causality by stressing necessary causation, and that this has been part of the evolution of O/W from organizing framework to a tool for developing research design and causal modeling. In order to demonstrate this, as well as more fully develop the relationship between opportunity and willingness, a discussion of substitutability is in order. An important corollary of O/W presented in Most and Starr (1989, chap. 5), substitutability refers to the existence of a set of alternative modes of response by which decision-makers could deal with some situation. This is what Cioffi-Revilla and Starr (1995, pp. 456–457) call “alternative modes of redundancy.” Substitutability indicates that any single cause may have multiple effects, and that any single effect may have multiple causes. Different problems may lead to similar responses; a given problem may be dealt with in multiple ways. And thus, for any given set of conditions, the same policy choice is not equally likely across time or space for elites. Substitutability, then, lies at the heart of the use of agent-structure frameworks like opportunity and willingness, where the choices of agents are analyzed in regard to the contextual structures within which they exist. Most and Starr (1989) argue that opportunity and willingness can operationally occur or be made available in any number of alternative, non-unique ways (as in the discussion of equifinality below).

A second corollary introduced by Most and Starr (1989) involved nice laws. The contextuality of O/W, along with its introduction of complex causal relationships, additionally suggests that it may be useful to expect that true social laws may not always hold, operate, or apply empirically. They argue that there are a variety of social laws, each of which is true but which should be expected to hold only under certain—perhaps very special—conditions. While it is possible that universals—always-true laws—exist, and Most and Starr believe that scholars should continue their efforts to identify such laws, it is difficult to think of very many empirical universals that have been identified by even physical scientists. Thus, it may be more useful to recognize that there could very well be laws that are in some sense “good,” “domain-specific,” or in Boynton’s terminology (1982), “nice,” even though the relationships that they imply are not necessarily empirically general. Rather than assuming that there need be a single always-true law that accounts for a given phenomenon whenever and wherever it has occurred or will occur, it may be more productive to think of laws each of which is (always) true under certain conditions (or within certain domains) but which is only “sometimes true” empirically because those conditions do not always hold in the empirical world.

This is the flip side of substitutability where a number of ways to bring about a certain condition or event may exist. With multiple factors in the environment that are sufficient to provide opportunity and multiple factors that are sufficient to bring about willingness, the idea of “nice laws” is clearly implied. A theoretical causal relationship may only actually be found under specific combinations of these factors (see the brief discussion of INUS causation below). Together, nice laws, substitutability, and their relationship to O/W tell us much about the nature of theory and the development of proper research designs to evaluate it. Most and Starr stress that the idea of nice laws also enables us to understand how apparently “contending” theories could all be “true”—each holding only under specific conditions that could change across time and/or space (e.g., some might work in a bipolar world of nuclear powers, and others in a multi-polar world of colonial powers, as in 19th-century Europe).

Returning to substitutability, Cioffi-Revilla and Starr (1995) demonstrate that it is not simply that substitutable modes (or redundancy) are related to greater “complexity” in the world—these modes actually make political behavior in a complex world more possible, and thus address the question of what types of behavior would be more or less likely and under what conditions. As argued by Most and Starr (e.g., 2015, preface), this is a view of complexity that has not been adequately addressed by realism, neo-realism, or most variants of transnational liberalism (see also Most & Starr, 1989, pp. 120–121). How can this be the case?

Using opportunity, willingness, and substitutability, Cioffi-Revilla and Starr (1995) present two orders of causality. They present a first-order causality of world politics, “causal necessity” (1995, p. 449), at the analytical level. As jointly necessary conditions, both opportunity and willingness must be present for any behavior to occur. This is distinct from a deeper second-order causality of substitutability at the operational level. What are the various factors, conditions, or resources that could provide opportunity? What are the various factors, conditions, or resources that could provide willingness? Cioffi-Revilla and Starr (1995, p. 454) ask, “Specifically (operationally) how do willingness and opportunity occur for any given political actor?” The answer to these questions is provided by substitutability. Any of a wide range of factors (that occur across levels of analysis and academic disciplines) might be sufficient (singly or in combination) to provide the needed opportunity or the needed willingness (i.e., cross the thresholds previously discussed). Cioffi-Revilla and Starr use Boolean logic to formalize and analyze the political uncertainty of international behavior, mathematically deriving a number of interesting insights into the agent-structure problem, especially in regard to the relationship between agency and structure. They demonstrate the relationships between first- and second- order causality. At the top are the first-order (necessary) elements of opportunity and willingness, which are linked by the Boolean AND (which represents necessity). Beneath each of these elements, there is a range of possible modes of (sufficient) second-order substitutability. These substitutable modes are connected by the Boolean OR (which represents sufficiency). Keep in mind that any set of substitutable modes could delineate a nice law that holds only under those conditions. Cioffi-Revilla and Starr (1995) clearly demonstrate the many possible ways in which the joint condition of opportunity and willingness can be achieved, and the important non-intuitive implications that can be derived through formal analyses.

These implications include the nature of causality (possibility and probability), the importance of recognizing and designing research to take necessity into account, and the use of counterfactuals. Much of this has been summarized by Friedman and Starr (1997, pp. 8–9):

For example, [Cioffi-Revilla and Starr] demonstrate that “the basic laws” that govern the occurrence of political events in real world politics are nonlinear and often counterintuitive. On the one hand, regarding first-order causality, “international behavior is always less likely than the necessary conditions (willingness and opportunity) that bring it about” (1995, p. 469, emphasis added). However, when looking at second-order causality, willingness and opportunity “are always more likely to occur than any of the substitutable modes (operational events taken from an actor’s ‘menu for choice’) that specifically produce them” (1995, p. 469, emphasis added). Cioffi-Revilla and Starr’s model, by dealing with the linkages between opportunity and willingness, also explains the phenomenon of turbulence—change and complexity—in world politics. They present proofs to indicate that as new and substitutable forms of opportunity and willingness increase, they induce sharp increases in the observed variety and frequency of international behaviors. These analyses cast the notions of causality, proximity, and historical context into an entirely new light.

Necessity, Sufficiency, and Complex Causality: O/W’s Role

Cioffi-Revilla and Starr also distinguish between the “real” world, where both opportunity and willingness are necessary, and what a counterfactual world would look like if only one of them would be needed for an event to occur. In the counterfactual world, if the possibility of action existed, it would occur because willingness would not be required (e.g., on any day, any country of the world could expect to be erased by U.S. nuclear weapons). Similarly, in the counterfactual world just being willing for something to happen would, in the immortal words of Captain Picard, “make it so” (e.g., if Monaco were willing to destroy Portugal with nuclear weapons, it would happen—opportunity not being necessary). Similarly, Cioffi-Revilla and Starr note (1995, p. 453): “deterrence could work when either credibility of intent or credibility of capability was available to dissuade aggressors—it would not be necessary for both events to occur. Clearly such a world is antithetical to ours, with political events triggered at a fantastic rate for lack of causal conjunction [that is, joint necessity of O/W] … Since politics in the real world is governed by causal conjunction, not by disjunction, this makes—quite literally—a world of a difference.”

The logic of necessary conditions and the importance of necessity as a form of causation (see Goertz & Starr, 2003) invariably include the use of counterfactuals—that some event could not have happened without the existence of some factor or condition, or that some threshold of a factor of condition had been passed (see, e.g., Goertz & Levy, 2007).

With the introduction of necessity and counterfactuals, we now have a number of interlocking features that provide the core of O/W and its theoretical importance. With O/W as jointly necessary—representing causal conjunction—and with substitutability providing the multiple paths for the existence of opportunity and willingness, we find that O/W is no mere organizing principle, but a potentially important model of causal complexity. A number of scholars in recent years have grappled with causal complexity in its many forms, explicitly citing and including substitutability as one type of equifinality. Goertz and Mahoney (2005, p. 501), for example, use equifinality to mean “that various conditions are sufficient to produce the same outcome and hence there are multiple paths to the same outcome.” Braumoeller, in his major statement on complex causality (2003, p. 209), similarly defines equifinality as having “multiple causal paths.”

Contingency plays a large part in such causal complexity—that some theory or hypothesis will hold only under certain conditions, or that a pair of “contending” theories may both be true under different conditions or contingencies (i.e., nice laws). In many cases, contingency is expressed as a necessary condition, without which some effect, outcome, or other dependent condition could not occur. This is why necessity is a key component of a philosophical view of causality becoming more prominent in the literature—the INUS (Insufficient but Nonredundant [i.e., necessary] part of an Unnecessary but Sufficient condition) view of causation. Mahoney and Goertz (2006, p. 232) provide a succinct explanation: “An INUS cause is neither individually necessary nor individually sufficient for an outcome. Instead it is one cause within a combination of causes that are jointly sufficient for an outcome. Thus, with this approach, scholars seek to identify combinations of variable values that are sufficient for outcomes of interest. The approach assumes that distinct combinations may each be sufficient, such that there are multiple paths to the same outcome …” Research findings with INUS causes can often be formally expressed through Boolean equations such as Y = (A AND B AND C) OR (C AND D AND E).

This description of contingency and INUS causation summarizes the important place of O/W in the development of causal models and the research designs by which to evaluate them. Regarding the latter, Most and Starr (1989) demonstrated that, while many relationships under study were those of a necessary causal relationship, the designs created to study those relationships were only relevant to hypotheses of sufficiency. Their major concern with getting the relationships among theory, logic, and research design correctly specified—with O/W in mind—focused on the disconnect between necessity, the logic of necessary causation, and the general differences between how necessity can and should be studied in comparison to sufficiency. These arguments have subsequently been raised and much further developed by political methodology scholars, such as Braumoeller and Goertz (2000), Goertz (2003), and Schrodt (2006). Goertz, for example, has drawn the contrast between a “necessary condition hypothesis,” which might propose that some minimum level of variable X is necessary for an outcome variable Y, to a “correlational hypothesis,” which would propose that the greater the value of some X, then the greater the value of some Y.4 Schrodt (2006) presents a similar critique of the “linear frequentist orthodoxy” of standard statistical models built for the study of sufficiency. As noted in the work of Braumoeller (2006), while we are trained to model changes in central tendency, necessary conditions imply a complex range of patterns that have nothing to do with central tendency or sufficient relationships.

O/W thus pushes the researcher to survey a range of methodological approaches and logically connect the most appropriate design to the question and phenomenon at hand. O/W has helped to point out that research designs (the nature of the theoretical logic and research hypotheses being employed) built around these different forms of causation will affect—and be affected by—the nature and types of the cases selected, the controls employed for dealing with possible other (explanatory) factors, and the methods used for evaluating the theory and proposed research hypotheses.

Let us look at one substantive example. Not understanding the differences between causal models of necessity and sufficiency is a key factor in disagreements over how to study deterrence and evaluate the models used to do so. For example, analysts such as Frank Harvey (1998, 1999) have usefully and appropriately raised the issue that theories or models of deterrence are models of necessity not sufficiency, but that critics of those models test them with designs only appropriate for sufficiency. It is interesting to highlight the parallels between critics of rational models of deterrence and critics of Bueno de Mesquita’s expected utility theory (e.g., Bueno de Mesquita, 1981, 1985). As discussed in Most and Starr (1989, pp. 56–57) critics charged Bueno de Mesquita’s model of “over-prediction.” In both the cases of deterrence and rational choice, analysts are proposing models of how people are supposed to behave if (and only if) certain processes are at work. Neither process is itself observable; indeed, deterrence is about actions that do not occur. Both theories set out conditions that must be present in order for certain outcomes—the results of these processes—to occur (i.e., necessary conditions). Neither theory is presented in an “if-then” structure that represents sufficiency. However, while the conditions may obtain, the proposed results may not appear. This startles the critics of such approaches.

Yet, this is exactly what is to be expected with models of necessity, and it is what makes them difficult to test. As Most and Starr (1989, pp. 56–57) point out in regard to expected utility, the number of cases that occur in a cell where the conditions of expected utility obtain but no conflict initiation occurs is irrelevant—because those conditions represent necessity not sufficiency; the only cell of importance is the one where an event occurs but the necessary conditions are absent. Note carefully that this corresponds directly to arguments by Lebow and Stein (1989) and similar critics that deterrence theory fails because, while all the conditions for deterrence are present, there is no deterrence. In Bueno de Mesquita’s expected utility analysis—where positive expected utility is a necessary condition for the decision to go to war—no conflict initiation reflects the nonoccurrence of behavior (e.g., see Bueno de Mesquita, 1984, for his response to critics). With deterrence, critics do not realize that they are in the same boat, because a lack of deterrence is reflected in some party actually behaving—initiating an attack or making a challenge of some kind. Using Most and Starr’s research triad of logic, theory, and research design, it is clear what is happening. The critics of such models of necessity think that the sort of behavior they can see permits them to treat the relationship as a sufficient relationship. It does not.

Note that substitutability plus O/W complicate research design, as well as the need for designs that capture necessary causation. But this is actually a strength of the O/W approach. For example, substitutability and O/W force the analyst out of single-variable or single-indicator ways of thinking about political phenomena or by under-specifying the theory being used. Only by understanding the broader concept or phenomenon under study (as argued in Most and Starr) could the researcher fully grasp exactly what one should be investigating in terms of the full range of operational observations (combining substitutability and nice laws). Focusing on only one mode of response, one causal factor, or one causal path would mean a failure to provide full coverage of the possible outcomes and lead to incomplete results that failed to cumulate (or even make sense when compared). The results would fail to capture the theory or model being tested. Additionally, focusing on only one possible outcome raises problems in identifying necessary and/or sufficient causality.


To summarize briefly, the O/W approach is useful in dealing with the basic tasks of any empirical theory. It is a useful and important way to organize the ways we think about international politics. It does this by providing a way to synthesize what we know and bring together apparently disparate hypotheses and evidence to bear—crossing a variety of analytic boundaries and pulling together what we know across levels of analysis, academic disciplines, and the sub-disciplines of political science. O/W complements theories built around levels of analysis, while at the same time moving them forward in order to deal with the complex causation they have to confront. O/W fulfills the tasks of theory as an intellectual tool and guide. By crossing methodological boundaries as well, it is a particularly useful guide to the development of research hypotheses and the research designs by which to evaluate them.

Recall that one of the problems identified by William Thompson was that “our theoretical testing approaches tend to be fragmented and not always cumulative.” O/W, as a theoretical agent-structure approach has important things to say about synthesis, as well as theoretical and empirical cumulation. As an agent-structure approach and as part of Most and Starr’s critical logic, O/W is not limited to any specific area of international politics or political science (see, e.g., the title of Cioffi-Revilla & Starr, 1995). Nor is it limited to any specific methodological tradition.5 O/W is part of an approach used to develop principles of valid and useful research design that could be applied to any empirical study, across methodologies, and to all aspects of research design—as long as one’s true enterprise is to investigate some aspect of the empirical world.

Because this article is primarily about O/W as a theoretical formulation, I have said little about the substantive empirical content of studies that use O/W as part of the theoretical foundation of a research project. Another reason is the one just mentioned—O/W should be applicable to any piece of empirical research about political behavior (I’m sure there must be exceptions, but none come to mind). Only a very few examples of research that use O/W will be noted below; a Google Scholar search of “opportunity and willingness” came up with over 1,300 articles, books, chapters, and papers—many with “opportunity and willingness” in their titles!

O/W is often most associated with geopolitical or spatially oriented conflict studies, looking at geospatial location or positioning, distance, borders, territory, and any other spatial factors related to the idea of “relevant” dyads, especially in regard to the spread of conflict or other conflict processes. This includes most studies that involve positive diffusion in its various forms and definitions. Such studies almost always stress opportunity, environment, or context. Thus, O/W features strongly in almost all of the empirical work on diffusion and borders by Starr and colleagues (summarized in Starr, 2013) and the diffusion of conflict in general (e.g., see Braithwaite, 2006). O/W also can be prominently found in the environmental and geopolitical studies flowing from PRIO scholars (see, e.g., Furlong, Gleditsch, & Hegre, 2006; Buhaug, Gates, & Lujala, 2009) or such eclectic works on conflict as Gleditsch (2002).

Beyond geopolitical applications, O/W has been the basis for studies of conflict in general (e.g., Clark & Regan, 2003) and such varied topics as arms production (Kinsella, 2000), nuclear proliferation (Jo & Gartzke, 2007), power parity (Lemke & Werner, 1996), and politically active dyads (Quackenbush, 2006), just to name a few of the disparate areas of application. The two-level security management project of Simon and Starr uses O/W and substitutability to build simulations that study the links between internal and external conflict, and the tradeoffs between internal and external security (1996). In Simon and Starr (2000), for example, they show how new and endangered democracies can provide internal security when larger and established democracies in the system can provide their external security. Indeed, substitutability has been a major or central concern in a number of empirical works, with important contributions to the research design employed. See especially the contributions to the special issue of the Journal of Conflict Resolution devoted to substitutability (Palmer, 2000; Palmer & Morgan, 2006). I hope this short discussion conveys the range of empirical studies to which O/W has been applied in the study of IR.

A final comment: Because cumulation rests not only on valid research design, but also on the validity of the empirical results, one is drawn back to Thompson’s first problem dealing with the “structure of the theoretical argument.” Following Most and Starr’s admonition to understand the logical form of the relationship generated by a theory, the discussion of O/W inevitably returns to the relationship between O/W and the logical causal structures of necessity and sufficiency. This begins with the central consequence of applying O/W—that opportunity and willingness are jointly necessary conditions for any action to occur. This not only distinguishes O/W from theoretical approaches that are deterministic, monocausal, rely on only single factors, or are concerned only with either opportunity or willingness—but is also the beginning of a logical story that demonstrates how O/W can at least begin to deal with causal complexity. The joint necessity of O/W along with substitutability and nice laws forces a researcher to more fully specify the logical and substantive structure of the theoretical statements under investigation. It also forces the researcher to make sure that the research design is relevant to the theory and research hypothesis, that there is a coherent relationship among the components of logic, theory, and method. At the end of the logical story (and the addition of substitutability and nice laws), we see that O/W has moved well beyond an organizing principle to a model of causal complexity with great potential.


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(1.) Friedman and Starr (1997; p. 3) note that this concern has been widespread and was central to the thinking of Durkheim, Weber, and Marx.

(2.) See Starr (2006) for a fuller discussion of how and why scholars need to “cross boundaries,” and Friedman and Starr (1997) regarding O/W, ontology, and epistemology.

(3.) For the development of O/W, this will continue to be an area of theoretical and empirical inquiry. Other such areas of future work include dealing with the challenges of studying substitutability, and especially how and when to cut into the endogenous feedback loops between willingness and opportunity, as they represent agency and structure.

(4.) As essentially representing necessary causation, based on presence or absence by crossing a threshold, it has never been argued that greater amounts of opportunity or willingness make some event or outcome more likely.

(5.) In this sense, the development of O/W preceded such important work as King, Keohane, and Verba’s (1994) unified approach to inference and Gerring’s (2005) unified framework for dealing with causation.