Much has been written about the relationship between religion and violence, and much of what has been written is aimed at determining whether, how, and why religion causes violence. This book has a different goal. Followers of many different religions who commit violent acts seek to justify these by appealing to religion. I aim to understand how such justifications proceed; and how they do, or do not, differ from ordinary secular justifications for violence. I will show that religious justifications for violence generally exemplify the same logical forms as ordinary secular justifications for violence. I will also show that many religiously based justifications for violence are as acceptable as rigorous secular justifications for violence, provided that crucial premises, which religion supplies, are accepted. Religious believers are able to incorporate premises, grounded in the metaphysics of religious worldviews, in arguments for the conclusion that this or that violent act is justified. I examine three widely employed types of premises that appear in such arguments. These are: appeals to a state of “cosmic war,” appeals to the afterlife, and appeals to sacred values.

The first three chapters of the book contain background material. Because my analysis is informed by recent work in psychology, cognitive science, neuroscience, and evolutionary biology, there is much ground to cover before we analyze religious justifications for violence. In Chapter 1, some violent actions that have been undertaken in the name of religion are discussed and two influential views about the relationship between religion, justification, and violence (or the lack of such a relationship) are considered and rejected. I also discuss and define the key terms “justification” and “violence,” as well as examine the relationship between nature and “supernature,” which underpins many of the metaphysical postulates developed by the religious. In the second chapter, I discuss influential generalizations about religion and assess which of these stands up to scientific scrutiny. I argue that religion has evolved and I consider competing views about how this has happened. I argue in favor of the view that religion is an evolutionary adaptation. I then offer a new, empirically informed, definition of religion. Chapter 3 is about morality. I consider the evolution of morality, the role of culture in shaping morality, and recent work in social psychology and neuroscience on moral judgment. All of this leads up to an overall characterization of the relationship between morality and religion. Readers who are well informed about any of the background topics discussed in Chapters 1, 2, and 3 may safely skip over the sections in which these topics are discussed.

In Chapter 4 I consider ordinary secular justifications for violence and explore how these can be reconciled with consequentialist and deontological accounts of morality. I then look at the ethics of war, just war theory, and pacifist objections to war. I also consider traditional religious justifications for war, many of which involve the supposition that a cosmic struggle is taking place between the forces of good and the forces of evil. I show that appeals to cosmic war make it easy to justify a range of behavior that would be harder to justify in conventional wars by the standards of just war theory. In Chapter 5, the role that afterlife beliefs can play in justifying religious violence is considered. I concentrate on arguments in the Christian tradition that appeal to the importance of salvation to justify violent actions directed at heretics and apostates, as well as arguments in the Buddhist tradition that appeal to beliefs about the cycle of reincarnation to justify violence. I also examine religious justifications for suicide that appeal to the afterlife. In Chapter 6, I consider the role that sacred values play in religious justifications of violence. I look at Durkheim's classic analysis of the sacred, as well as recent work in psychology and negotiation studies on sacred values, along with some contemporary work in cognitive science and neuroscience on sacralization. I end the chapter by arguing that ordinary reasoning about sacred values is a form of ordinary deontological moral reasoning.

Chapter 7 contains a series of recent case studies in which violent action has been taken, and religious justifications for this violence have been offered, either by the perpetrators, or by sympathetic co-religionists. Six case studies are examined. I look at two religious groups from the United States, The Gatekeepers and Heaven's Gate, and also a religiously inspired American anti-abortion activist, Scott Roeder. I consider a religious group based in Japan, Aum Shinrikyo, as well as followers of the Rabbi Meir Kahane, who have committed acts of violence in Israel. Lastly, I consider religious justifications for violence offered by representatives of the international organization al-Qaeda. In all six case studies, it is demonstrated that the justifications offered for violent action carried out in the name of religion appeal to cosmic war, the afterlife, or sacred values, or some combination of these three factors.

Chapter 8 is about religious tolerance. I consider what tolerance is and how religious tolerance is justified in liberal democratic states. I then examine evidence from social psychology about whether religion promotes tolerance or intolerance. I go on to consider whether promoting the value of religious tolerance could be an effective way to persuade those who believe that they are justified by their religion in acting violently to refrain from acting violently. In Chapter 9, I consider some other possible ways to persuade those who believe that violent action is justified by religion, and who are motivated to act violently, to nevertheless refrain from acting violently. I also consider whether, and to what extent, religiously tolerant liberal societies can and should tolerate religious groups that believe that they are justified in acting violently on behalf of their religion.

Throughout the book I follow a common, abbreviated way of writing and refer to attempted justifications simply as justifications. It should be clear enough, from context, when I am referring to an attempt to justify some or other doctrine, or instance of violent action, and when I am referring to justifications that meet the standards that we ordinarily accept as successfully justifying violent action. The justification of any form of violence is a controversial topic and there will be some readers who will not regard the standards that most people ordinarily accept as justifying violent action as sufficiently rigorous. Some readers will hold that we ought to apply more rigorous standards to all attempts to justify violence, including those that appeal to religion. Other readers, especially avid pacifists, will suppose that we can never offer successful justifications for any violent behaviour. Although I discuss pacifist objections to war in Chapter 4, a proper consideration of pacifist objections to the standards that most of us ordinarily apply to justifications of violence is beyond the scope of this work.

The book had its origins in a grant application, on “Science and Religious Conflict'” which I developed, together with Julian Savulescu, director of the Oxford Uehiro Centre for Practical Ethics, the Institute for Science and Ethics, in the Oxford Martin School, and the Oxford Centre for Neuroethics, all at the University of Oxford. Julian and I wanted to take recent work in social psychology, cognitive science, neuroscience and evolutionary biology and apply this to shed light on the nature of religious conflict; and also to suggest ways to reduce religious conflict. Our application was generously funded by the Arts and Humanities Research Council in the United Kingdom and ran from the beginning of 2009 to mid-2012 (Standard Grant AH/F019513/1). In addition to this book, the Science and Religious Conflict project resulted in two major international conferences, a number of academic papers, and an edited volume, Religion, Intolerance and Conflict: A Scientific and Conceptual Investigation, edited by Steve Clarke, Russell Powell, and Julian Savulescu (Oxford: Oxford University Press 2013). Julian and I were fortunate enough to have been able to employ Russell Powell to work on the grant. I benefited enormously from the opportunity to work with Julian and Russell, as well as the opportunity to work at the Uehiro Centre and in the Oxford Martin School. Work on the latter stages of this book was generously supported by the Centre for Applied Philosophy and Public Ethics, Charles Sturt University.

Thanks to Joanna Burch-Brown, Adrienne Clarke, Katrien Devolder, Tom Douglas, David Edmonds, Jacqueline Fox, Guy Kahane, Marguerite La Caze, Neil Levy, Morgan Luck, Kate MacDonald, Terry MacDonald, Francesca Minerva, Justin Oakley, Russell Powell, Simon Rippon, Julian Savulescu, Nicholas Shea, John Teehan, Steven Tudor, Adrian Walsh, and several anonymous reviewers for helping me to improve my draft material. Thanks also to Lindsay Bourgeois, Michael Boylan, Jennifer Bray, Liam Cooper, Jeff Dean, Allison Kostka, Louise Spencely, and Paul Stringer for their editorial help and support.