This is a major contribution to the literature on the morality of war, written in two voices, one argumentative, the other reflective and open to other perspectives. In Defence of War is, on the one hand, a rich reflection on a wealth of literature, historical and contemporary, addressing the justifications for making war. The chapters – developed on the basis of a series of essays already published elsewhere – span the historical development of just war theory, at the same time addressing at length contemporary arguments about the justifications for embarking upon the First World War, the invasion of Iraq in 2003 and the intervention by NATO militaries in Kosovo in 1999. On the other hand, the work is also a focused polemic against recent pacifist and liberal literature. The theological project which sustains this polemic is a careful argument explaining why war is justified where it conforms to the notion of right intention, which must be understood in relation to the works of Augustine. The two voices need not appear to conflict for a reader whose interest lies primarily in the proper understanding of Christian texts on war. They are more evident for the reviewer interested in the impact In Defence of War may have beyond the churches, and particularly for readers who seek to grasp the practical gains suggested either by the book's principal argument about intention or by the series of discursive chapters which may enable a number of advances in the literature regardless of whether this argument proves unassailable.

There have been numerous reviews of the book focused on the relationship between text, theology and contemporary ethical frameworks for the justification of war, but respondents have still to relate this volume convincingly to the literature on just war. In order to identify the book's innovative approach, a first priority is to give an appropriate level of attention to Biggar's intention. The work is based on engagement with a very diverse set of intellectual resources and subjects, making it unwise to jump to easy assumptions about the book's argument even where these appear to present themselves in the introductory chapter. In this introduction Biggar notes that his attention to war derives from a personal fascination, evident not only in the historical reading and reflection offered in the book, but also in the discussions the author has maintained over the past decades with interlocutors from the military and with specialists from around the world, whose approach to thinking about just and unjust wars is consequently framed in terms of very different intellectual resources, whether these be Catholics, secularist philosophers or, more recently, Confucian-inspired thinkers in China. At the same time, Biggar's core arguments are clearly motivated by the sense that the readiness of Christians to justify military force with appropriate discretion has been attenuated by foggy thinking. His solution is to return us to the theological convictions which were midwife to the development of classic reflections on just war before the onset of rights-based liberalism.

The essays through which he constructs his case are therefore deliberately polemical, expressly written in the knowledge that many of his judgements will be controversial. Listed, they would prompt many readers to place Biggar in contemporary terms on the political right and to read his essays as the predictable complaint of an irascible opponent of liberal values. And, to be sure, the author is concerned to define a morality which offers a permissive basis for decisions about war. This is juxtaposed to the commonplace notion that the just war tradition proceeds from a presumption against making war unless a series of prescriptions about consequences are clearly fulfilled in advance. The book is also peppered with a recurrent dismissal of Enlightenment liberalism as over-optimistic and befuddled by an incoherent discourse about rights and legality. Whereas, Biggar holds, scholars interested in liberal and in pacifist thought have commonly demonstrated a muddled understanding of the classic Christian just war tradition, these essays indicate how we may recover the moral realism which is expressed in that body of literature and apply it to the contemporary wars in which Britain has been involved. And here the tension between the two voices begins to grow, as readers seek to understand how far the targets of the book's polemic are chosen because they are politically and intellectually troubling, or, on the contrary, the extent to which they merit our attention because of their apparent strengths – strengths which, it seems, the author himself appreciates.

While Nigel Biggar presents a masterfully effective argumentative voice, he is never merely a polemicist. In Defence of War is particularly careful to suggest the grounds for common reflection with liberals concerned to establish a coherent or philosophically rigorous moral apparatus capable of supporting better decisions about necessary and unnecessary war. If readers are minded to examine the conversations Biggar invites beyond his polemic, the book reads very differently, as a respectful opening to a discussion about how such a moral foundation may apply in practice, given the limitations to what we can know with a degree of certainty about practicality and right intention in today's wars.

The book's first substantive chapter is primarily concerned with the reading of Christian scriptures, engaging with a set of recent Christian pacifist texts which attack just war theory with the aid of a particular reading of the New Testament. Biggar frankly rejects these, even while acknowledging the appeal of this body of literature for a thinking, caring Christian: they merit attention here precisely because they appear to have a great impact on theologians and on the churches in the English-speaking world. The influence of a combination of Anabaptist and Marxist-Hegelian politics on this literature, inspired by John Howard Yoder, has not prevented its broad assimilation in academic and popular literature on war and Christian ethics. While political, theological and denominational differences will make an obvious target for readers interested in this chapter, the chapter's primary target is the lack of precision with which the New Testament is read by Yoder, by his disciple Hauerwas, and even by the more circumspect pacifist New Testament scholar, Richard Hays. Their judgements about the canonical or faithful reading of New Testament texts about the sin associated with taking up the sword and of working as soldiers are seen to be laced with political assumptions, demanding the prior acceptance of dualistic thinking about power and agency that make war a tragic consequence of the ever-present will to imperial domination. These assumptions run contrary to those of Biggar's avowedly Augustinian perspective, according to which the same texts provide a confirmation of the legitimacy of the use of force in accounts of the actions and thought of Jesus and Paul. There is clearly a great deal at play in the framing of this polemic. The argument does not simplistically dismiss pacifists as naïve idealists. While Biggar does argue for a Christian realism, he is also inspired by Barth's theological anthropology, which sets out grounds for hope in the face of evil. Yet the chapter suggests a particular kind of Barthian, and this aspect of Biggar's theology deserves further comment. The Old Testament, or the Hebrew scriptures, receives little attention here, in spite of the importance of biblical hermeneutics both for Biggar's moral realism and for Barth's notion of biblical theology. This may in part reflect Biggar's christology. It probably also reflects the fact that his polemic in this chapter is against a set of writers who prefer a thoroughly New Testament theology, as is common amongst many Anabaptist thinkers influenced by the historic peace churches. While clearly an important resource in Christian thinking about just war, the Old Testament is identified here with holy war and religious nationalism, concepts which Biggar is keen to contrast with authentic just war literature. Such a distinction is greatly at variance with the classic Christian texts on the criteria for a just war, and closely matches the account of Yoder. There is a point of contact with Barth's thinking, but the result is that this book does not provide a reading of many of the texts that have been influential in Christian debates about war.

The next two chapters substantiate Biggar's judgement that a Christian is morally obliged to recognise that, even in today's industrial and technological wars, soldiers commonly exercise a proper sense of moral judgement. If this argument fails, killing in war could be seen to be murder. Biggar's solution could be understood as eschewing a meaningful sense of proportion and discrimination, instead favouring a definition of right intention as the primary criterion in the justification of a war fought by a legitimate authority. This right intention is not a pure intention – it can be mixed with ulterior motives, so long as the foundational intention is correct. It is this view of right intention as foundational for action that gives an individual soldier the capacity to kill an enemy with regret. Where the act of killing is a consequence of a greater intention, he continues, the moral justification of lethal action may be witnessed in evidence that it is not the act of killing itself that is intended. The same construction of intention is also the foundation of a proper perspective on the grounds on which a state makes war. A state may be expected to have potential ulterior motives, particularly if the state has the capacity to make war effectively, but these need not obviate a proper judgement based on right intention. In order to establish right intention, it is not necessary to consider all of the possible consequences of a decision to make war, since it is the intended results of a decision to make war which provide a foundation for judgements about right intention.

Here Biggar's contribution will be understood differently. He is writing with readers in mind who are uncomfortable with the idea that war can be justified even if it leads to enormous scales of killing. It is certainly not necessary that readers lose their discomfort for the intended purpose to have been served, that being to show how decisions about killing can be made in the real world and yet with a proper moral foundation. In Defence of War repeatedly notes that the realism advanced here primarily addresses the reality of human evil: it is specifically moral realism, and political and legal realisms ought properly to be seen as secondary to that. In this light, some of the distinctions drawn in prior literature are also seen to be of secondary importance. Predominantly, texts on just war criteria have not used proportionality and discrimination as determinants of the decision to go to war, deploying them instead to decisions made once war is declared (i.e. in bello). In this respect, the present work may appear an interesting departure from the norm, perhaps part of a larger project to show what moral decisions look like when the distinction between jus ad bellum and jus in bello is not accepted, or minimised.

Perhaps in response to the nature of the public debate over the necessity and morality of war, In Defence of War focuses on ad bellum considerations, and not on the preparation of soldiers or of generals for fighting justly. It remains unclear whether the primacy of right intention in calculations about fighting itself means that military professionals are to be granted a certain latitude about their approach to killing in the field. Here, the professional or lay reader alike may desire to know if the book should be read as a statement that, regardless of how carefully soldiers make distinctions and calculate necessity or proportionality, wars cannot be fought in more or less moral ways. Biggar's argument against relying upon our ability to agree upon prudential calculations is intended to solidify the argument in favour of a permissive approach to judging right intention, without expecting the professional to calculate likely or unintended consequences. Doubtless some readers will be concerned that the text does not argue for careful prudential calculation. The work is not, however, dismissive of the sense of morality of a professional who believes that their careful conduct may make them more moral than a brutal enemy; in other words, that combat can be conducted in better or worse fashions, and not only either in a just or unjust manner.

If the polemic form of the book increases possibilities for variant readings based on alternative perspectives or assumptions about the intention behind its publication, a positive consequence may be that this will facilitate renewed discussion about the nature and possibility of moral warfare. A number of powerful Christian writers, philosophers and theologians alike, have argued that the asymmetric threats faced by Western armies today require a return to classic or to medieval just war texts, which shaped the terms of discussion before a secular version of just war theory presented itself, either in the nineteenth or in the twentieth century. Warfare now, it is said, means facing a terrorism which mocks the prudential proprieties of a liberal school of just war theorising, with its assumptions about just wars being inherently defensive, and about the burden of evidence being against making war if prudential criteria are not met. The conditions faced in fighting terrorists make sense of a return to the medieval foundations of just war thinking, when wars were understood as punitive actions against criminals, without the constraints placed on action by a liberal international order.

In Defence of War has much in common with a number of such works, notably the seminal contributions by Oliver O'Donovan and Jean Bethke Elshtain. And yet it is distinctive in ways that suggest particular lines of dialogue about the problems of assertions about just wars. Biggar identifies the weakness of much contemporary just war literature with a liberal and secularist legal positivism. This positivism carries the assumption that state activity is to be justified based on its efficacy in the defence of the rights of the individual, which Biggar questions. His final lengthy dialogue is with a critical voice, David Rodin, who assumes that perspective only to reject it. Biggar respectfully seeks to show that Rodin makes cogent criticisms of just war theory which only work if the theory is judged by the assumptions of liberals who identify the justifications of state actions with the rights of individuals to life and liberty. Historically a Lockean position, the argument in favour of life and liberty as foundations for practical state ethics is currently being given renewed attention as a foundation for ethical doctrine within the British and US militaries, in part thanks to the influence of Rodin. In a rich discussion of early modern just war literature, Biggar shows that early modern texts which provided the intellectual foundations for modern and secular liberal just war literature – by Grotius, Suarez and Vattel – do not assume a right to life; and rather than grounding international relations in an abstract commitment to the defence of individual rights, they were firmly grounded in Christian commitments that explained the duty of the state to engage in warfare as a permissive obligation to act punitively when faced with wrongdoers. Seeking to dethrone individual rights as absolute determinants of imperative action, the essays nevertheless advance a dialogue with liberal thinkers. In this regard, Biggar foregrounds the work of generations of early modern thinkers who appreciate the value of secular arguments for a transcendent international law. Although this is not his concern, these writers were also significant for their increasing concentration on prudential criteria, which become a touchstone for the moral conduct of warfare. Whereas for Biggar the prudential criteria are of secondary importance in working out a moral judgement in response to the tragedy attendant to even a justified war, the prudential criteria were of primary importance for seminal writers in the early modern period: they became important because of the developing scholastic concern not to evince a minimal respect for human life but to maximise this respect. This sensibility provides continuing motivation for much of the voluminous just war literature published in the last fifteen years.

As already noted, two voices compete in this work. One is polemical: more categorical, controversial and combative. The other is more respectful and modest: here, the author is encouraging further discussion between interlocutors with fundamentally different perspectives, not seeking to conclude a debate with a convincing fact or rejoinder. To the extent that both voices are worth engaging with, even necessary for an understanding of Biggar's project to revalue intention as the primary criterion for assessing the morality of ad bellum and in bello calculations, then the polemic is a form well chosen. The categorical demand for a moral theory of war which is internally coherent remains clear throughout the essays presented here, but the polemical form allows the author to keep readers aware of the limitations of the common academic view that a just war theory must primarily be judged by its theoretical consistency, rather than by its credibility as a resource for the interpretation of real experience.