In modern warfare, when is it permissible to kill? A new book authored by Professor of Law Alec Walen examines prevailing opinions—and offers his own perspective—on when killing in war is justified and when it violates a person's moral rights. 

We discussed his book, "The Mechanics of Claims and Permissible Killing in War," in a Q&A. 

Tell us a little bit about your new book.

My book spells out and argues for a new theory of moral rights and applies it to topics in just war theory. Unlike some views on moral rights, the “mechanics of claims” take rights seriously as more than a label we happen to throw on certain moral reasons for or against acting. That is, it takes seriously the idea that there is something truly distinctive about saying that one has a right that another must respect, or that one has a right to act.

Moreover, unlike some other views on rights that take rights to give extra force to certain kinds of interests, the mechanics of claims gives a systematic account of rights that appeals to three basic principles: that we are all free to lead our own lives primarily for our own ends, as long as we respect the rights of others too; that we are all equal members of the community of rights holders; and that our welfare matters when it comes to assigning the rights we have. These principles ground accounts of some basic features of rights, such as that they are fundamentally relational, that it is harder to justify treating people as a means than harming them as a side effect, and that it is easier to justify harming people who are threats to others than mere bystanders, unless they have a right to threaten.

Who is this book for?

This book is for moral philosophers, legal theorists, lawyers and policy analysts who want to understand better the nature of rights generally and the revisionist approach to just war theory that holds that war may be waged only when doing so respects the rights of the individuals affected.

What is a “permissible killing” in war?

It is permissible to kill when doing so does not violate anyone’s rights. There are three basic ways to justify killing in war. First, those who threaten others when they lack the right to threaten may lack the right not to be killed if killing them will protect others who have a right not to be killed. This applies both to unjust combatants and to those who help unjust combatants wage war. Second, where there is a sufficiently strong justification for using force, it may outweigh the claims of people who are not threats but mere bystanders, who would be killed as a side effect of that act. Third, in the case of unjust combatants, it is often permissible to kill some to deter others from engaging in unjust combat. My project focuses on the first two justifications for killing in war.

Your book defends the idea that it is easier to justify intentionally killing an innocent threat than killing an innocent bystander as a side effect. What does this look like in action?

A civilian who provides aid to unjust combatants is an indirect threat to those unjustly threatened by the combatant. If she does not know that she is aiding unjust combatants, she may be morally innocent. Yet, in virtue of helping those combatants, it may be easier to justify targeting her than killing other civilians as a side effect. This is quite contrary to traditional just war theory. But the implication is not as radical as it may seem.

Generally, it will not be permissible to target civilians because it would be hard to meaningfully reduce the aid they provide to unjust combatants without killing so many that it would be disproportional to the good achieved. There will also normally be other options that are less harmful, making killing civilians both unnecessary and disproportional, and thus doubly impermissible. But on some occasions, civilians with special skills, such as fundraising or weapons development, may be important targets to save innocent lives.

The point of my argument is that we do not need to worry about whether they have forfeited their right not to be killed. The mere fact that they are helping unjust combatants wage an unjust war makes the justification for targeting them easier to justify than collateral damage on the same scale.

What initially drew you to study the philosophical foundations of moral rights and criminal law?

I was drawn into criminal law by my work in moral philosophy. I have long thought about some basic principles in moral philosophy: for instance, intentional harming is harder to justify than harming with foresight; using as a means is harder to justify than harming as a side effect. I was drawn into the world of criminal law theory because people in that world were told that I had some interesting views on these principles, which are of obvious relevance to questions about what is ultimately justifiable, and thus what is ultimately beyond the realm of proper criminalization. I then was invited to comment on a recent book in just war theory, which took me outside the realm of criminal law, but got me thinking about threats. That caused me to realize that my view of rights was too simple, and the effort to develop it to account for what we can do to threats led quickly to this book.

What else do you do at Rutgers University?

My bread and butter course is criminal law, which I teach nearly every year for the law school. I have also taught it for undergraduates in New Brunswick. I also taught a philosophy course on rights theory twice to undergraduates, and last year to graduate students in New Brunswick. I have also taught the philosophy of criminal law and counter-terrorism as well as national security law. All of these have some bearing on the work of the book.

What will you be working on next?

I have a number of papers lined up, on topics ranging from forfeiture and self-defense, to the justification of overinclusive criminal laws, to causation in the criminal law, to the relevance of wrongdoing to torts, to understanding better how to handle risk in moral philosophy. But the big project coming up is another book under contract with Oxford University Press. While this book was about rights and the use of lethal force, the next book will be about rights and detention of the dangerous. The working title is Detention in a Liberal State.