David Boucher's The Limits of Ethics in International Relations is the result of eleven years’ hard work. It shows a degree of ambition that is unfortunately rare in the current REF-driven environment, in terms of the period that it covers (from the Ancient Greeks to the present), the length of the book, and the level of scholarship. The result is a deeply impressive achievement, containing a wealth of original and nuanced interpretation, especially in the chapters on modern political thought. Boucher does not attempt to paper over discontinuities between the various positions covered, ensuring that his analysis reflects much of the complex and fragmentary character of over two thousand years of writings on natural law, natural rights, and human rights. As a result, the book is a similarly complex and diverse body of work.

Boucher derives a unity from his core contentions ‘that natural law and natural rights, as constellations of ideas and presuppositions, are far more in harmony with each other than most commentators are prepared to admit, and that natural rights and human rights are far more conceptually distinct than is often maintained’ (p. 3). As one might expect of one of the world's leading authorities on the philosophy of R. G. Collingwood, Boucher is particularly sensitive to the presuppositions of the positions that he examines. By exploring their conceptual and propositional substrata, Boucher reveals new complexities within many of the theories. In this way, he resists the conflation of natural law and the law of nature, as well as highlighting what he argues are presently misunderstood fundamental differences between both of them and natural right(s) and the law of nations.

The Limits of Ethics in International Relations has twelve main chapters. In the first, Boucher traces the development of Ancient Greek and Roman conceptions of ‘natural law and the law of nations’. The recurring themes in this discussion of Plato, Aristotle, the Epicureans, the Stoics, and the Cynics include the various attempts to manage the differing perceived demands of ‘nature’ and those of human artifice (not least in the guise of law). He argues that the resulting tensions manifest themselves in various ways: in attempts to reconcile prescription and description, reason and emotion, and the virtues of the individual and the good of the community. Chapter 2 examines medieval theories of natural law, paying particular attention to the ways in which earlier Greek and Roman conceptions were revised in the light of Christian concerns and presuppositions. Chapter 3 considers the relationships between (rationalist) natural law and the (customary) Law of Nations in the likes of Grotius, Pufendorf, and Rachel, before considering the historical appearance of natural rights. Crudely, one might summarize Boucher's claim as being that this latter shift is from an understanding of the moral universe as a realm in which individuals confront a series of external divinely ordained constraints, to one in which rights are qualities given by God to individuals themselves. Chapter 4 (‘Natural Rights and Social Exclusion: Cultural Encounters’) covers issues of early-modern colonialism, such as have been highlighted previously by James Tully and others. Chapter 5 distinguishes ‘descriptive’ natural rights from ‘prescriptive’ ones, the former being rights derived from the natural qualities of individuals and the latter being divinely ordained commandments. Boucher credits Thomas Hobbes with being the ‘finest exponent’ of descriptive rights (although they themselves were ‘something of an aberration’ in the history of rights discourse) and ‘Locke, Price, Priestly, Paine, and Wollstonecraft’ as the most notable exponents of prescriptive rights (p. 141). Chapter 6 considers Hume, Rousseau, Burke, and other eighteenth-century critics of natural rights theory. The effects of their respective attacks on the efficacy of natural rights discourse is the subject of chapter 7, where Boucher turns to the practices of and resistances to slavery and racism between the sixteenth and early nineteenth centuries, noting among many other things, Kant's racist attitudes regarding Africans (p. 197).

Chapter 8 constitutes the pivot of the book, in that it concerns the point at which doctrines of natural rights began to be transformed into doctrines of human rights. The chapter begins with a comparison of Bentham and Marx, before turning to de Tocqueville and then to Hegel. The majority of the chapter is devoted to the British idealists, and especially to T. H. Green and D. G. Ritchie. Their related critiques of atomistic individualism and slavery lead into a discussion of moral ideals extending beyond the nation. Boucher sees the British idealists as being significant because they were the first both to radically reinterpret Christianity and to use that reinterpretation as the basis of a new form of rights theory: ‘They emphasize the historical dimension in the emergence of fundamental rights, but continue to employ a strong foundationalism in embedding the rights in a conception of universal reason and self-realization’ (p. 243).

Boucher argues that the British idealists’ transformation of God from an essentially external divinity into a divinity immanent within every individual led to a radical secularisation of the natural rights tradition. He traces this transformation in the final four chapters the book. Chapter 9 analyses the development of international human rights culture, through an analysis of the founding principles of the League of Nations, United Nations, Universal Declaration of Human Rights, and various other similar bodies and documents. The chapter extends this analysis by considering what Boucher sees as an associated ‘communitarian’ turn in the writings of such as Arendt, Collingwood, and Rorty. Chapter 10 develops this latter move via an examination of certain ‘modern constitutive theories of human rights’, especially Constructivism and the English School in international relations theory and the reworking of the British idealists’ rights recognition theory by such as Gaus and Martin, and even Rawls in The Law of Peoples. Chapter 11 considers the ‘juridical revolution’ in human rights discourse, focusing on such issues as genocide and the rise of international humanitarian law following the Nuremberg trials. Chapter 12 considers the rise of gender as a fundamental human rights issue, via a rereading of many of the preceding thinkers in light of the effective silence of women in their works. Once again, Boucher shows the crucial role played by the British idealists in laying the basis for gender equality in human rights theories, through both their philosophy and their practical activities (for example, in relation to helping to secure for women a right to take higher degrees, and in their opposition to the Contagious Diseases Act) (pp. 338–42). Boucher examines also the definition and rights of (non-)combatants and the use of rape in war. In the ‘Conclusion’, Boucher emphasizes the fact that the present human rights culture is relatively new and remains very much a work-in-progress. Ultimately, he argues: ‘We should not, however, be discouraged.’

Boucher is to be congratulated for not trying to overly systematise the series of theories he covers. He shows a level of respect for the integrity of his chosen works and movements that, sadly, remains unusual in historical works of this wide-ranging, thematic type. He draws out the individualities of his chosen thinkers, thereby highlighting both their similarities with their forebears and their divergences from them. Nevertheless, this does not mean that the result is confused. Boucher states his guiding claim using the Collingwoodian metaphor of ‘question and answer’: ‘I will argue that natural law, natural rights (both prescriptive and descriptive), and human rights are conceptually distinct, but are related to each other, not as answers to the same question, but as part of the same historical process by which one turns into the other’ (p. 3). Specifically, Boucher argues that the natural rights tradition relied on irreducibly religious foundations which gradually have been shed on human rights theories. In this way, he argues that the secularization of rights discourse occurred much later than many scholars believe. This claim is significant because it undermines the positions of contemporary political philosophers who appeal to the writings of, for example, John Locke to develop an essentially atheistic theory of rights.

Boucher's debts to Collingwood bring him very significant benefits. Most significantly, his contextualism focuses tightly on the texts themselves in a way that contemporary contextualists including many ‘classical’ and later Skinnerians do not. It is true that Boucher's method gives his analysis less of the aesthetic sweep that appeals to many other historians. Yet, this is no bad thing for those who aspire to present a properly historical analysis. Frequently those who seek an aesthetic sweep in their histories obscure and distort their analyses in ways that Boucher's application of a Collingwoodian method rarely does. Boucher demonstrates how one can read a text carefully in its appropriate wider context without being seduced by interesting incidents of only speculative relevance to the writings under discussion.

Throughout, Boucher's analysis is concise and self-assured. While this does give engaging tone, pace, and sweep to the book, it also has certain pitfalls. Occasionally it is a little difficult to identify the nuances of the line of argument being defended, greater textual evidence (both in terms of quotation and referencing) would have helped to establish certain claims, and aspects of Boucher's case could have been strengthened by explicitly identifying and rebutting alternative readings in a little greater depth. Yet, such problems seem almost inevitable with a work of this scale, and given the generally prohibitive economics of the alternative, multi-volume works. There was a choice to be made regarding what to include and just as much would have been lost as gained if Boucher had tried to include more in this already very long book. Moreover, it is important to note that these problems diminish as the work progresses and Boucher moves into the modern period. Ultimately, these concerns are more than offset by the very great strengths of Boucher's book. The Limits of Ethics in International Relations is a remarkable book that develops an ambitious, intelligent, well-informed, and original argument on a topic of fundamental contemporary importance.