Is international law really law? Does international law exhibit a moral purpose? These questions continue to plague the discipline. The responses of international lawyers have been varied but far from reassuring. Three kinds are identified at the outset of the book under review. First, Patrick Capps believes that, in relation to the ontological question, many international lawyers bury their heads in the sand (p. 19). Because international legal practice is well established, many international lawyers see theory as a distraction from the business of international law. Second, he notes that certain theoreticians are sceptical about the nature of the international legal project, either because its legal traditions are incommensurable and inconstantFootnote ¹ or because they are demonstrably ill-egalitarian (pp. 11–18).Footnote ² However, the third approach identified by Capps is more optimistic in tone. It claims that international law is a progressive, purposive, and practical endeavour (pp. 19–21). This position is most notable in the work of Hersch Lauterpacht. Capps locates himself in this tradition and he attempts to provide its theoretical underpinnings, principally from the works of Kant, Rousseau, and Hobbes. He reconstructs these philosophical resources to argue for the epistemic primacy of a concept of international law which is founded on a respect for human dignity (p. 16).

The book is divided into two parts. The first part (chapters 1 to 5) engages in a rigorous investigation of the methodology of law and, in turn, international law. This part is incisive and highly persuasive, even if the reader does not subscribe to idealistic perspectives or the natural law tradition. One of the main themes of the book is how our a priori judgements affect our general conception of law. Capps suggests that legal scientists have not attached sufficient weight to the way in which our preconceptions influence our conception of law (p. 26). He endorses the position adopted by Finnis that the raw data from which we glean our viewpoints about the nature of things is unstable.Footnote ³ Rather than finding convergence in the raw data, we unconsciously select what we think is important from it according to our a priori judgements. Consequently, Austin's conclusion that international law is merely positive morality and Hart's view that it is a peripheral case of law were drawn from their own preconceived judgements about the concept of international law. Capps shows that the same is true for Anghie's view that international law is inherently imperialistic in nature (pp. 27–32).

If one's view of law is grounded in one's a priori judgement, it seems possible to adjust our conceptual starting point via language use or by drawing conceptual distinctions from our social practices so that the central case of law can be extended to encompass paradigm cases of international law, thereby solving the existential problem. However, Capps believes that the conceptual problem will endure unless we acknowledge that the purpose of law informs our general conception of law (pp. 40–2 and chapter 3). He argues, via Aristotle's conception of friendship, that all social practices have focal characteristics and that, consequently, all forms of law are purposive phenomena rooted in morality (pp. 43–6 and chapter 4). But who decides the moral purpose of a particular form of law? Capps thinks that the legal scientist must perform this task (pp. 47–8). But, according to Capps, the legal scientist does not simply substantiate her subjective a priori judgement of the raw data; instead, she adopts a non-arbitrary view based on a practically reasonable interpretation of its purpose. The resultant view then conditions the concept of that particular form of law (pp. 101–2). Sceptical scholars might argue that we cannot have objective knowledge of the concept of law and, in turn, international law, and that the test of reasonableness is merely a cover for the subjective preferences of the legal scientist in question. Capps disagrees strongly with this position (pp. 21, 102). He argues that the practically reasonable point of view is a moral one, and he uses the philosophical works of Kant, Rousseau, Hobbes, Weber, and Aristotle to support his claim that international law is purposively orientated to the achievement of human dignity.

The second part of the book (chapters 6 to 10) addresses this claim. Capps argues that human dignity only exists when human beings can exercise their autonomy, and law guarantees this freedom via the provision of a set of human rights (p. 108). For Capps, human dignity is founded on the notion that human agents must be allowed to achieve their purpose (p. 114). He acknowledges that there is no moral consensus on a set of basic moral values (p. 115). Nonetheless, he argues, via Kant's categorical imperative, that all human beings are morally bound to respect the autonomy of the recipients of their will. This duty imposes moral constraints on their actions that cannot be renounced without contradicting the position that human beings are endowed with will (p. 116). According to Capps, Kant thought that we needed law in order to coerce human agents, because their actions are often immoral and irrational, into respecting the autonomy of others (p. 124). Consequently, for him, law creates a protected sphere in which human beings can exercise their autonomy via the creation of a set of human rights. In Rousseau's proto-Kantian terms, through law the general will restructures social relations to lessen community members’ dependence on one another, thereby enhancing their freedom and human dignity (pp. 177–84).

In order to co-ordinate social activity in a way that will enable coexistence, law must be separated from other forms of practical reasoning (such as morality or politics). Capps terms this the ‘Autonomy Thesis’ and he explores various aspects of it throughout chapter 6. He shows that the Autonomy Thesis has a long philosophical tradition (as apparent from the works of Hobbes and Bentham) and within international legal scholarship (notably in the writings of Oppenheim and Weil). Capps notes that, on an orthodox reading, the Autonomy Thesis creates a limited domain that isolates law from other forms of practical reasoning, thus enabling it to perform its co-ordinating function (the ‘limited domain thesis’) (pp. 131–2). Further, the Autonomy Thesis forestalls and conditions certain claims because they are not considered to be legally relevant in the light of the law's operation or content (‘the pre-emption thesis’) (pp. 142–6). However, Capps challenges the view that law can be genuinely isolated from other forms of practical reasoning. He argues that the bare version of the Autonomy Thesis is unworkable in practice because it cannot resolve legal disputes in accordance with the limited-domain thesis. He claims that legal decision-makers must decide disputes by reference to considerations which are located beyond the legal domain. This manoeuvre also compromises the pre-emptive thesis by making the law less predictable and less fair, since the law is being influenced by non-legal considerations (pp. 149–53). The author claims that this problem can be solved by developing an integrated version of the Autonomy Thesis, one that incorporates the element of practical reasoning from a moral point of view. He suggests that background reasons that are excluded from the bare Autonomy Thesis should be brought within law's ambit to promote transparency and predictable, authoritative decision-making in the interests of justice. These reasons should be public in nature and must be ‘those that all members of a community can accept as reasonable’ (p. 153). A sceptic might argue that the background reasons which may be used to guide or balance a particular decision will not be known in advance and, as a consequence, this proposal would prove to be of little practical use. Capps appreciates this counter-argument, but he believes that a reconstructed version of Kant's work, one that emphasizes the capacity of rational agents to will rather than the ends to which that will is put, presupposes limits based on the notion of human dignity (pp. 136–9 and chapter 7). Capps argues that those limits are discernible from the practically reasonable point of view (p. 153).

In chapter 8, Capps shows that the Autonomy Thesis seems to fit well in the international context. The Hegelian idea that freedom is constituted by the state and the Kantian notion that war is not a rightful condition can be harnessed to support the sovereignty of international law. However, the moral agency argument appears to be less successful. Capps acknowledges that states do not have intrinsic moral rights. Instead he argues that they have collateral moral rights because they act on behalf of their citizens, who are endowed with moral agency (pp. 193–4). For him, the position of states in the international legal order is broadly analogous to the position of the individual within state legal orders. Consequently, states have collateral moral value and moral rights, such as the right to non-interference and to participate in international relations (pp. 259–60). They also have concomitant moral obligations. Capps asserts that states have moral obligations not only to their citizens but also to other states. He harnesses solidarist values to this end by emphasizing states’ dual function as both the subjects and administrators of international law (pp. 205–8). Therefore Capps plausibly transposes the Kantian claim concerning the autonomy of human agents and the associated moral constraints imposed on their will to the context of international relations. For him, ‘it is surely irrational to will an international legal order which is not designed to attempt to be consistent with morality’ (p. 202). By conjoining Kant's moral philosophy with his distinct work on international law, Capps justifies the application of his integrated model of the Autonomy Thesis to the international legal order (pp. 201–3). As a result, he establishes a meaningful theoretical framework through which to assess the foundations of international law.

On the issue of institutional design, Capps ultimately accepts the practical limits imposed on solidarism by the current institutional architecture. He therefore endorses Lauterpacht's opinion that the existing inter-state system can support a nascent international legal order (pp. 209–11). For Capps, international law acts as ‘an omni-lateral will which concretizes the relations between States and it implies legal institutions which create, interpret and enforce international legal norms’ (p. 243). However, in chapter 10 he distinguishes between the international legal order that follows from ideal and non-ideal theory. In the former, states can be trusted to create and administer the international legal order with limited assistance from supra-state institutions, especially in relation to dispute resolution. However, in non-ideal theory, the considerable scope for moral disagreement between states means that more extensive supra-state governance is required. Capps then explains how his concept of international law could support an emergent international legal order in both ideal and non-ideal theory via a discussion of norm-creation, interpretation, and enforcement, paying particular attention to the concept of statehood in these situations.

Capps believes that a range of constitutional sources – including the UN Charter, the Vienna Convention on the Law of Treaties, the draft Articles on State Responsibility and the International Covenants on Human Rights – show that a nascent international legal order exists and that this order is oriented towards the achievement of human dignity (see pp. 106–8, 211–12, and chapter 10 generally). He mentions briefly how international instruments, such as the Universal Declaration of Human Rights, and the concept of jus cogens evidence the moral foundations of this fledgling order (pp. 106, 155). However, Capps makes it clear that it is not his aim ‘to chart the commonalities between various normative practices, individuated norms and institutions which we normally refer to as international law’ (pp. 274–5). Instead, the aim of the book under review is ‘to offer a methodologically defensible explanation of the essential features of international law’ (p. 275). To some extent this aim is based on the assumption that elements of an international legal order are already discernible in the normative practices and the paradigm cases of international law. This may be true, and Capps does make a number of thought-provoking observations (particularly in relation to the concept of statehood, pp. 258–65) in support of this claim. However, it is not comprehensively tested in this book. Arguably, Capps's methodological defence of international law warrants a more sustained examination of the present condition of international law and of the practical implications of his theoretical model for that form of law if his book is to satisfy better his goal of articulating the moral foundations of the international legal system. Notwithstanding this criticism, his book represents a substantial contribution to the progressive interpretation tradition pioneered by Lauterpacht, and it can be seen as an important call to like-minded international lawyers to engage in practically focused research that builds on the theoretical foundations laid out in the present book.

Capps's ability to reconstruct and interpret the works of Hobbes, Rousseau, and Kant in support of his core thesis is impressive. He endorses Rawls's view that Kant's work can be used to underpin a ‘realistic utopia’. For Capps, ‘Kant thought that if we can make states better, they could undertake institutional roles in the administration of the international legal order’ (p. 7). However, using Kant's work to found an argument for a morally inspired international legal order is problematic for a number of reasons. First, Kant is usually seen as endorsing the bare version of the Autonomy Thesis of which Capps is so critical. Kant was careful to separate his moral philosophy from his prescriptions regarding international law. This divide has greatly influenced the writings of Habermas and Kelsen. Capps, however, believes that this separation was a mistake and that we should take a more holistic view of Kant's work (p. 202). Capps's position has considerable merit, and it can be seen as part of a wider move to connect these disparate areas of Kant's scholarship.Footnote ⁴ Second, it is not entirely clear that Kant envisaged international normative practices as an approximation rather than an analogue to international law (pp. 237–41). Capps suggests that Kant did not think that international law was impossible and that, if he had had the benefit of our subsequent experience, he would have concluded that an international legal order was entirely possible (pp. 240–1). This point may be conjectural but it does fit within Kant's moral philosophy. Finally, Capps doubts whether Kant would have endorsed his core thesis (that an international legal order must be rooted in respect for human dignity). However, he thinks that Kant was simply mistaken in this regard (p. 274). Again, this conclusion is plausible if Kant's moral philosophy is seen as overriding his work on international law. Nevertheless, Capps clearly has his work cut out for him in making Kant's writings fit into his theoretical mould. In part, this is one of the general challenges of producing a work of legal philosophy but it also stems from the inconsistencies within Kant's body of work and the practical implications of Kantian theories for international law and the existing institutional architecture of international relations.

Capps's theoretical conclusions about the nature of international law lead him to the view that if normative practices, which are ordinarily called international law, do not meet the standard of human dignity, as judged from the reasonably practical point of view, then such practices cannot really be international law (p. 271). Consequently, the international law which underpinned European colonialism so effectively cannot legitimately be called international law (a position which, in turn, undermines Anghie's view that international law is inherently imperialistic) (p. 212). This raises the question of the temporal scope of international law. Capps's theorizing seems to be largely future-oriented. It appears that an international legal order was established in the recent past. Perhaps it was constituted through the founding of the United Nations system (or at some point during its immediate aftermath). However, many of the current normative practices that are widely perceived as international law would also fail the test of human dignity and thus cannot be called international law either. This may cause the reader to ask a blunt question: what is the current condition of the international legal order? Capps indicates that the progressive interpretative approach ‘employs the concept of international law to interpret our various paradigm cases and normative practices as attempts to establish an international law order. To the extent that they are successful in doing this we can say that the international legal order, in an ontological sense, exists’ (p. 7, emphasis in original). Accordingly, the international legal order exists, but to what extent has it been realized in the normative practices and paradigm cases of international law?

In chapter 3, Capps sets great store on the viewpoints of the legal officials who participate in a legal system and the way in which their self-perceptions inform our general conception of law. Further, at the start of the book, Capps makes the point that his theoretical conclusions are unlikely to influence international lawyers unless they are persuaded by the cogency of his arguments (p. 10). The reader might wonder to what extent international lawyers will be convinced by Capps's arguments in the absence of a comprehensive discussion of the extent to which current normative practices reflect Capps's theoretical model. As noted above, Capps makes it clear that his enquiry is not concerned with this question. However, his references to the constitutional sources of the international legal order, his significant discussion on the creation, interpretation, and enforcement of international law in ideal and non-ideal theory, and his views about those normative practices which can properly be termed international law together indicate that some attempt at assessing the current state of the international legal order could have helped to persuade more international lawyers of the undoubted merits of his theoretical arguments.

The most fundamental theoretical question raised in Capps's book arises from the use of the concept of rationality as a basis for determining whether the rules and principles of law/international law are consistent with the achievement of human dignity. The Kantian view seems to suggest that the practically reasonable point of view is one on which we can all agree and that the standard of human dignity means that moral autonomy renders all human rights and obligations compatible. Rationality can be used to find the morally right answer and thus avoid the political contests which otherwise underpin legal disputes in the arena of the state (or between states on the international stage). However, an alternative position is that there is a broad range of divergent, but reasonably practical, points of view and that therefore the appeal to rationality does not resolve questions of justice in practice.Footnote ⁵ The claim that law/international law is oriented towards respect for human dignity may make it easier to incorporate certain moral considerations into processes of legal decision-making. However, it does not negate the political nature of such processes, because rationality does not engender commensurability either inside or outside the state.

The acknowledgement that a plurality of rational, but incompatible, positions exists in the context of any legal dispute justifies a comprehensive enquiry into the practicalities of achieving global justice. This does not undermine the importance of theory but it does move us beyond the realm of philosophy. Further, the use of the work of such scholars as Kant in order to provide the basis for a kind of global law begs the question why the international legal order should be derived, essentially, from the thinking of Europeans. The charge that international law is fundamentally Eurocentric is difficult to defend against. The work of scholars such as Anghie is important because they give voice to the biases and blind spots of international law and, in turn, they try to make international law a more inclusive project by orienting it away from its European origins. Legal theory is indeed moving away from these origins, and in the light of this shift theoreticians should also explore the intellectual resources of other legal traditions in their efforts to found a global legal order.Footnote ⁶