It is commonly said that "all is fair in love and war": soldiers have the moral right to kill other soldiers in wartime whether or not their cause is just. One reason is that soldiers are permitted to act in self-defence. A second reason is that peacetime morality is suspended in wartime: war makes things different and what was once morally impermissible becomes permissible, even glorified. These and other widely held, venerable views are frankly exploded - please excuse the pun - in this book, with great clarity and tremendous persuasive force.
Are soldiers morally justified in killing other soldiers in combat? Not always. As an example, the justness of their cause matters significantly. For Jeff McMahan, soldiers lacking a just cause should no longer be understood to have any moral right to kill soldiers that possess a just cause. This is because soldiers lacking a just cause also lack a right to harm.
Our killing in war can be justified only where we have a just cause - and, thus, a justified reason to kill. It does not make sense to argue that soldiers lacking a just cause are justified in killing others when these soldiers lack a justified reason for their aggression in the first place.
Soldiers should also be held to account for their actions. This breaks with the commonly held view that political leaders, not soldiers, should be held to account for wartime activity.
Of course, we may hold soldiers, not their political masters, responsible for war crimes. Thus, we do believe soldiers are accountable in some circumstances.
Furthermore, soldiers are not protected from blameworthiness when fighting on behalf of an unjust cause so long as they adhere to standard wartime conventions. Indeed, soldiers are legally required to disobey unlawful commands concerning wartime conduct. McMahan argues that this should be extended: soldiers should also be able to disobey orders to fight in a war they believe is unjust.
One reason is that we all have a negative duty to avoid harming innocent people. Soldiers honour this negative duty when choosing against fighting in an unjust war where innocent people will be killed. Could such a plan be feasibly enacted? McMahan outlines precisely how this may be achieved.
We may think that war simply makes things different: it may be true that we would be most morally upright doing one thing rather than another, but war significantly changes the scenario, such as suspending or altering our normal moral judgments.
However, McMahan convincingly argues this cannot be true. His example is an army lacking a just cause that brutalises and terrorises a community. Members of this community then band together to launch guerrilla counter-attacks on the invaders. The army may find itself under attack, but it would have no right to self-defence. This is because it had no right to launch an unjust aggression. This example highlights that our normal moral standards hold irrespective of wartime: it is a mistake to think otherwise.
I found this work so thoroughly convincing that it is difficult to raise many criticisms, although I will briefly note one. McMahan's project is "to bring the law of war into closer conformity with the morality of war", not unlike the way in which criminal law has been brought into conformity with morality. While I readily grant that this project has many benefits, I am more cautious.
First, it is the case that the criminal law unites morality and law imperfectly at best: some crimes may be "wrong in themselves" (or mala in se), but others may be "wrong on account of their being prohibited" (or mala prohibita). If the criminal law is to serve as a guide, then which aspects of the law of war should remain separate of morality as with mala prohibita crimes?
Second, criminal law develops within a particular community whereas the law of war is global. Is there a global morality? I do not doubt that there is significant overlap on morality internationally.
However, there remain significant differences and any international morality will have important limitations, none of which is dealt with here. Morality is a sphere of difference and it remains unclear how much universal appeal McMahan's understanding of morality will have. This is not to say that I disagree with him, but only that more should be said.
Nevertheless, Killing in War represents a tremendous achievement from one of today's leading moral philosophers. Never before has a book so swiftly challenged my own views and convinced me that I was in error. I cannot recommend it highly enough.
Killing in War
By Jeff McMahan. Oxford University Press. 2pp, £19.99. ISBN 9780199548668. Published 23 April 2009