Is international law really law? If it is law, is it effective in constraining state behavior against interest? These two questions have vexed international lawyers and those international relations scholars interested in international law who until the last 15 years or so were relatively few in number. There has been a proliferation of scholarship on these questions, and on bridging the gap between international relations and international law (IL). (To note only one recent survey piece, see Anne-Marie Slaughter, Andrew Tulumello, and Stephan Wood, “International Law and International Relations Theory: A New Generation of Interdisciplinary scholarship,” American Journal of International Law 92 [July 1998]: 367–397).

These two books offer dichotomous perspectives on the debate, and from unusual quarters. While international relations scholars have traditionally been more interested in the efficacy question, the volume edited by Christian Reus-Smit, a scholar of IR (although the volume contains multiple contributions by international lawyers) is more concerned with offering an account, through the lens of constructivism, of how international law functions. Meanwhile, the book by Jack Goldsmith and Eric Posner, two legal academics, is concerned with the efficacy question, using rational choice theory more familiar to political scientists. These books differ not just in their selection of motivating question and methodology but also in their assessment of international law. While the contributors to the Reus-Smit volume examine the function of law and the relation between law and norms in the international sphere, Goldsmith and Posner are convinced that international law itself has no direct effect on state behavior, but rather that it expresses the rational interests of states and that when it ceases to do so, it will not constrain them.

The impetus behind the two questions, and the source of the rift in the second half of the twentieth century between the related disciplines of IL and IR is well known to many scholars of both, and need not be rehearsed in much detail here. The questions and the rift have been driven by the dominance of realism in international relations scholarship, and, arguably, legal positivism in international legal scholarship. The former suggested that the absence of a “Leviathan” in the international sphere meant that international law could not be law as it could not constrain sovereign states (Reus-Smit, pp. 14–44). The latter suggested that international law lacked the requisites of law, either sovereign authority or the appropriate legal apparatus (legislature, executive, and judiciary). While a variety of arguments have been adduced in response to these challenges, for our purposes only the constructivist response of Reus-Smit and his contributors, and the further challenge from the rational choice theory of Goldsmith and Posner, are of concern.

Reus-Smit et al. place themselves squarely in a broad tradition in IR theory, constructivism (see, e.g., Alexander Wendt, Social Theory of International Politics, 1999). Constructivists reject the idea that politics is simply about power, or maximizing utility, and instead argue that not just structures but also norms and ideas can shape behavior, further that social identities shape interests and behavior, and finally that those identities are socially learned (Reus-Smit, pp. 21–22). Their collective argument, in direct challenge to realism, is that norms and law can shape state behavior, even against apparent interest, because that interest itself is not fixed but can change over time. They reject any suggestion that law and politics are distinct entities in the international sphere, and also the idea that law is just a function of politics, or is always constrained by it. Rather, they argue that there is a feedback effect, as law shapes actors' conceptions of their own interests. The constructivists' account of norm development, further, has a strong affinity with the account by lawyers of the development of customary international law (Richard Price, “Emerging Customary Norms and Anti-personnel Landmines,” in Reus-Smit, pp. 109–13). This account requires the presence of two elements: state practice and opinio juris, the belief of a state that the conduct is required. This element of belief is viewed by many constructivists as akin to the effect of norms upon identity, interest, and action.

The authors do this by examining the dynamics of law and politics in a variety of issue areas, including the use of force, the International Criminal Court, and international financial institutions. As with any edited volume, the contributions are uneven, but the message of the contributions is clear—international law really is law, and it does constrain state behavior. A helpful illustration may be provided by the chapter on the use of force (Dino Kritsiotis, “When States Use Armed Force,” pp. 45–79). The use of force is a classic example of high politics, an arena in which realists would least expect law to constrain power. This chapter, in examining the historical evolution of doctrines surrounding the use of force, describes law as a process: Rules are laid down limiting the use of force, but exceptions are also articulated. States seek to justify actions through reference to those exceptions, rather than simply rejecting the rule, suggesting that states do respect the law (Kritsiotis, pp. 63–78).

Taken together, the pieces in the volume offer a strong case for international law, and indeed the relationship between international relations and international law as process, rather than a set of fixed rules that are accepted or rejected by states. The strength of the volume is the shared theoretical perspective of all of the authors, constructivism. Yet that perspective is also ultimately limiting. As the introduction itself notes, scholars from other perspectives, such as liberal institutionalism, have also sought to establish a role for law in international politics. A volume with a plurality of theoretical perspectives might have ultimately offered a more fruitful set of arguments, particularly to do with the purported “legalization” of international life (International Organization 54 [no. 3, Summer 2000], special issue).

Goldsmith and Posner have a rather more skeptical take on international law, rejecting claims that it has any autonomous influence upon state behavior. Rather, drawing upon rational choice theory used by some IR scholars, they argue that international law is, at most, a codification or representation of state interests. States create international law and then “comply” with it, they argue, because it offers a rational solution to the prisoner's dilemma or other challenges of international interaction in the absence of full information, which can be modeled. International law simply offers a helpful mode for signaling, provision of information to prevent or punish cheating, and so on. The authors could have simply offered an institutionalist account of law but decline to do so, rejecting the common claims by such scholars that while law may originally serve coordination or information functions, it ultimately has its own constraining force (Goldsmith and Posner, p. 16). Rather, the authors would agree with realists that law will cease to constrain when it is not in state interests. They further reject that there are any noninstrumental reasons, such as norms or identity, that might lead states to comply with international law. They argue that four possible reasons exist for state behavior “associated with international law”: It arises merely because states have a coincidence of interest, is created to facilitate coordination or to facilitate collaboration, or is created to assist the coercion of the strong by the weak (pp. 11–14).

The authors offer detailed analyses of two types of international law—custom and treaty—in a number of domains, including use of force, human rights, and international trade. They are particularly skeptical of the force of custom, suggesting that many rules said to have reached the status of customary international law, such as the protection of civilian fishing vessels, have not, because in fact state practice is not as uniform as it is said to be, and the evidence of opinio juris is limited or also divergent. If such limited custom is problematic, then broader custom, such as “treaties are to be respected” (pacta sunt servanda), is even less likely to have substantive effect, according to the authors (pp. 14–15, 23–43). Rather, custom, like the development of treaties, serves a convenient function for states, helping them to calculate their interests and the likelihood that others will behave in a similar fashion. Goldman and Posner adduce similar arguments for the development of treaty law (81–162). They finally challenge the status of international law on rather different grounds—having sought to show that it is simply the result of rational choice calculations, they then argue that it also cannot be justified on coherent moral grounds (pp. 165–224). These arguments would appear to further challenge the constructivist emphasis upon norms having autonomous persuasive effects.

A review quotation from Anne-Marie Slaughter on the dust jacket says that Goldman and Posner “throw down a gauntlet likely to infuriate many traditional international lawyers.” This is undoubtedly the case, and the book will be the subject of much controversy. I will limit my remarks for reasons of space to two instances in which the authors seem to estimate the potentially concrete power of international law: the success of the European human rights regime and the rapid development of international human rights law, including that resulting in individual criminal accountability. The former is claimed to be an instance of federalism, rather than one of states complying with obligations against interest. Yet this is too simple a move, for confederations do not simply appear but may themselves be the result of law-conforming behavior and perhaps the influence of norms. The latter is said to be meaningless, for states incur little or no cost by signing human rights agreements, whether or not they ever intend to comply. But the dismissive view of the effect of human rights law fails to take account of costly developments, including those creating the ad hoc war crimes tribunals for Rwanda and the former Yugoslavia, and of the International Criminal Court, which appear to run against (some) state interests, and with which so many states have been engaged, even altering domestic legislation in order to better cooperate with the institutions.

Neither volume definitively settles the questions posed at the outset, and the engagement and debate between the disciplines of IR and IL is likely to continue for some time. Each of these volumes does, in its own way, offer an important contribution to that debate.