Ratner's Thin Justice of International Law attempts to bridge international law and philosophy (Chapter 1). Ratner asks a fundamental question: where is justice to be found in international law? His task is important because this question tends to be asked by political scientists or philosophers, rather than lawyers. Ratner examines the relationship between justice and international law from three different aspects: first, the transformation of moral prescriptions into legally binding international rules; second, the role of international law in forming our understanding of global justice; and, third, the morality of the rules and structures of international law. The contribution of Ratner's book to international legal scholarship lies in an obvious observation – but one that is underexplored by international lawyers – that many choices confronting international actors are ethical ones.

Ratner argues that the core norms of international law should conform to a standard of global justice (Chapter 2), which he terms ‘thin’ justice. He views it as resting on two ’pillars. The first pillar is their advancement of international peace and the second their conformity to human rights (Chapter 3). Ratner regards these two values as internal to the normative structure of international affairs, not just to international law (p. 65). Those core norms that do not meet the ‘thin’ justice standard are, under Ratner's definition, unjust. Reform of core norms and institutions of international law must meet the standard of ‘thin’ justice or aspire to a higher standard of global justice. Ratner then analyses certain aspects of the international legal order through the lens of global justice. Specifically, he evaluates whether the core norms on statehood (Chapters 4–7), the core norms created in response to the claims of states and people (Chapters 8 and 9), and the core norms on the global economy (Chapters 10–11) conform to a ‘thin’ justice standard. Ratner's book offers a framework to international law makers upon which to design the norms and institutions of the future.

My first observation regarding Ratner's thesis is the creation of a standard of justice by reference to peace. Some of the greatest thinkers in the history of mankind have attempted to define the question: what is justice? This notion tends to be associated with fairness, equity, impartiality, or even equality. I find it analytically problematic to propose a standard of justice by reference to the notion of peace because the two concepts are conceptually distinct. Peace is defined, at the most basic level, as the absence of armed conflict, and it tends to be associated with the notion of security in the United Nations Charter.Footnote ¹ At a more advanced level, peace is a multidimensional concept, empirically quantified by reference to a wide range of indicators.Footnote ² The notion of peace – be it basic or advanced – is distinct from even the most rudimentary definition of justice. Inevitably, when assessing whether certain core international norms are just, characterizations such as ‘(un)fair’ and ‘(un)equal’ make an unsurprising appearance in Ratner's book (e.g. Chapter 7).

My second observation regarding Ratner's thesis is the creation of standard of justice by reference to human rights. Ratner considers basic human rights to be a limited practice-based concept aimed at protecting individuals against the most serious threats to their integrity and welfare. While Ratner considers basic human rights as an ethically defensible principle of justice, they have also been the subject of a burgeoning number of international instruments.Footnote ³ The legal nature of human rights cannot be neglected. As such, the added value of examining whether international law conforms to a standard intrinsic to it is questionable. While Ratner recognizes the legalized nature of some aspects of morality (p. 8), a more useful exercise might have been the assessment of international law by reference to standards extrinsic to law. The argument that international law should be complied with because it conforms to other legal principles, which are incidentally moral, might not constitute ‘good reason’ for states to respect international law.

Ratner assesses several international norms by his ‘thin’ standard of justice, finding that either they are permitted or prohibited. What he is careful not to do is to require particular norms under his theory. That is better left to the realm of ‘ideal’ theory. Ratner concludes his book by considering certain limitations and aspirations (Chapters 12 and 13), proposing a thicker standard of international justice, while not crossing the boundary of ‘non-ideal’ theory. The ‘thick’ justice of international law judges the rules of international law by whether they advance human rights in a way that does not interfere with peace. This would involve reform of the core norms that do not meet the standard of ‘thin’ justice, such as for example humanitarian intervention without Security Council approval (Chapter 9). Ratner argues that the move towards thicker justice should be done in a way so as not to sacrifice the ‘thin’ justice achieved, even though it does not seem likely that such a risk is likely to materialize in practice.

Ratner seems to be an optimist visionary by considering international law as central to construction of a more just world order. He offers an additional reason as to why international law should be complied with, other than it being simply law: because it is just (p.4). Ratner argues that ‘the justness of particular rules will influence the proclivity of international actors to follow those rules’ (p. 14). What is unclear is whether states do in fact comply, if at all, with international law because it is just. Ratner does little in terms of substantiating the argument – even in its current form – as to why the rate of compliance of states with international law would be influenced by the ‘justness’ of its contents. To flip the argument around, little is done by way of examples of states disobeying international law because they consider it to be unjust or even examples of states having good reasons to disobey just rules.Footnote ⁴

Would a just international norm fare better in terms of compliance than an unjust law? Some might argue that states have no general obligation to obey international law and consequently would not comply with any international law, just or unjust.Footnote ⁵ Posner argues that ‘there is little reason to believe that the … [international] system is just … and that individuals throughout the world, or their governments, owe any duty to it.’Footnote ⁶ Others might argue that whether an international legal norm is just is an irrelevant consideration and they would point to the pacta sunt servanda rule as encapsulated in Article 26 of the Vienna Convention on the Law of Treaties.Footnote ⁷ Article 26 might have been reason enough for H. L. A. Hart, and amount to Kelsen's grundnorm of international law, for states to comply with international law, despite denying that it matters whether states have a moral obligation to obey international law.Footnote ⁸ Another way that Ratner's thesis could be viewed is through the lens of Article 31(1) of the Vienna Convention, which sets out the general rule of interpretation, namely that a treaty shall be interpreted in light of its object and purpose. Had Ratner's thesis been limited solely to the UN Charter, rather than the core norms of international law, which identifies as its object and purpose the maintenance of ‘international peace and security’ and the reaffirmation of ‘human rights’ in its Preamble, his thesis would have been entirely persuasive. But to evaluate, for example, international investment law by reference to a standard of peace, is less convincing because it does not constitute either its object or its purpose.

My response to Ratner is not a positivist one, namely one that would consider the moral content of law irrelevant to its status as law. Nor is my response a realist one, namely that international law is irrelevant to international relations. Rather, the difficulty with international law is that it cannot be distinguished from morality as easily as is the case with domestic law. Although treaties might be identified as international law without difficulty, the same is not the case with custom or general principles of law.Footnote ⁹ Morality – or justice, for that matter – seeps through international law, particularly when the latter is interpreted by an international tribunal. For example, the International Court of Justice is empowered to decide a case ex aequo et bono, if the parties agree thereto.Footnote ¹⁰ Even if the International Court of Justice were to apply the concept of ‘thin’ justice under Article 38(2) – assuming that equity and justice can be equated – one may reasonably expect a judgment to advance international peace, given that the Court's task is the peaceful settlement of international disputes, but not to apply human rights, unless it has jurisdiction to do so.Footnote ¹¹

Creating a more just international legal order by bridging justice with international law is a noble pursuit. While Ratner's endeavour focuses on whether existing international norms conform to his standard of justice – and assuming that this is the definition of justice by which law should be measured – I consider that the real problem lies not with international law per se, with certain notable exceptions as Ratner demonstrates, including the unrestricted veto of the five permanent members of the United Nations Security Council or a blanket ban on any aid to rebels fighting an atrocity-driven regime. The real shortcoming of international law is the degree of compliance of states, notwithstanding Henkin's maxim that ‘almost all nations observe almost all principles of international law and almost all of their obligations almost all of the time.’Footnote ¹² Finally, to my mind, international law is a tool, which can be moulded by the volonté of states (the English word ‘will’ does little to accurately describe what lies at the heart of state consent). Whether states will comply more often or to a higher degree with international law because it meets Ratner's ‘thin’ standard of justice is a question that could be empirically examined. I appreciate, however, that such a task would require another volume to be adequately analysed. What remains a nobler pursuit is for states to put Ratner's theory into practice.