Natural law is a subject which can belong to a number of distinct debates. The theological debate is about the standards by which non-believers can be judged as living good or bad lives. The moralist's debate is about whether facts about human nature can be used to derive moral norms governing human behaviour. The secular jurist's debate concerns the existence of universal standards by which posited human laws can be judged as good or bad. Natural Law: a Jewish, Christian and Islamic trialogue offers a set of discussions which predominantly concern the first debate. For the most part, the attention is on the classical period of debates in each of the religious traditions, so the focus is more historical than contemporary.

As the title suggests, this is a discussion of natural law undertaken by scholars of different faiths who are both familiar with the work of the others and are open to their insights. This is a work of genuine engagement and the structure is helpful in this regard. Each of the authors sets out in turn to present significant works in the formation of their tradition, and these are then the subject of shorter reflections by the other two authors. The book is well written and there is care taken to integrate the different presentations.

Because the works are historical in focus, they illustrate the way in which natural law was conceived at early stages in the three religions. They do not engage significantly with the preoccupations of the secular Enlightenment in Europe and the ways in which universalist discourse about moral values, such as fundamental human rights, has to be couched in order to make it accessible to the contemporary, non-religious reader. It is clear from short comments that these writers are perfectly capable of engaging in such discourse, and there would be much value in them producing such a work.

Novak helpfully defines the subject of the discussion in this book: ‘theistically formulated natural law is “natural”, not because it conforms to some larger cosmic scheme called “Nature”, but rather because this law is discovered by human beings when reasoning about the indispensable requirements of their created human nature’ (p 7, emphasis in original). Essentially, the authors’ concern is how moral standards of conduct derived by human reason from the contemplation of the natural order can be seen in some way as divine law. Natural law is not seen as an a theological parallel moral system but as an incomplete articulation of the divine law, which is more easily understood through revelation. It is readily possible to identify negative precepts from this form of natural law, such as not murdering or committing fraud, but it is less easy to derive positive precepts, such as loving one's neighbour.

Novak devotes the first chapter to presenting an understanding of natural law. Natural law is to be understood as articulating values we take for granted in our reasoning, whatever cultural or religious background we come from. But,

Debate then takes place by comparing the different universal horizons. Novak's universalism is seen as valuable by Emon because it provide a non-imperialist approach which can help in reasoned deliberation on the requirements of Islam. A focus on universal principles provides a perspective for checking the specific requirements of inherited doctrines (fiqh). Many of the latter are very general and Novak's view of natural law helps to offer a way of providing for concrete standards of behaviour without ignoring the cultural circumstances in which these have to operate. Levering also sees this as attractive in that it acknowledges that truth can be found in human natural law reasoning outside the Christian community. Scripture and revelation build on natural law. Indeed, for Novak, the Torah was seen largely as codifying what human beings already knew was for their good (p 40). The function of natural law may be as much to encourage rethinking of apparent requirements of the religious law (such as the apparent ethnic cleansing injunction of Deuteronomy 20:16) as to require secular rulers to change their human laws to fit natural law (see especially pp 40–41 and 51).

In his chapter, Levering looks at early patristic writing on natural law and revelation. How could non-Christians be good if they just knew and followed natural law? In writers such as St John Chrysostom, God is seen as giving natural law as well as the later Mosaic law, and humans are inherently capable of directing themselves towards the good and knowing when they are committing evil. Natural law is offered as a way in which the Gentiles can participate in God's providential plan for human beings. Yet there is a stress in Augustine and in much later theological writing that human beings are weak and so are in need of grace if they are actually to achieve the requirements of the natural law, if not the further requirements of the divine law relating to the relationship between God and humankind.

Emon, in his chapter on Islamic natural law, focuses on a distinction between hard natural law, where the empirical goodness of nature contains its normative content from God, and soft natural law, where nature needs to be interpreted in order to discover its inherent basic values. The fixed stability of what is is the source of authority. By contrast, the view that the requirements of natural law need to be identified by interpreters in a particular time and space arises from the indeterminacy of what can be observed in nature. But both approaches lead to the conclusion that no single human articulation of the requirements of natural law can be seen as authoritative. It would have been good if the discussion of mediaeval Islamic thought had been more clearly linked by Levering to discussion of its influence on Christian writers of the period. Instead, he tries to make a link from these debates to contemporary views such as those of Macintyre, which focus on the conditions for rational inquiry, rather than to specific content. This emphasises the point that, although there may be certain moral principles which are shared across cultures, once they are applied to the complex circumstances of life, natural law doctrine alone cannot do most of the work (p 195).

This collection offers interesting insights into the nature of natural law debate within a religious community – both its value and its limitations. The short discussions within the book about contemporary philosophy and human rights discourse suggest that the authors have much to contribute to an engagement with contemporary secularist scepticism about natural law, but that is for a future work. Their ability to converse well with each other suggests that the authors could equally well debate the issues with secularist writers and that would provide a clearer articulation of the contemporary relevance of their perspectives.