There are two central questions about the principle of noncombatant immunity. First, should we accept it at all? That is, should we believe that it is wrong to attack civilians? Second, if we do accept it, should we accept it as an absolute principle or as a principle that permits some justifiable exceptions? These questions focus on issues about who or what are permissible targets of attack. These are only some of the many questions that a full ethic of war will answer.

Some people may wonder whether it makes sense to apply ideas about the ethics of war to questions about terrorism. They may think it is not appropriate to apply ethical principles about warfare to violent attacks conducted by non-governmental groups. I have argued in several places (and will continue to do so) for the applicability of ethics of war principles to terrorist actions. One reason for this is that terrorist acts can be carried out by states as well as non-state groups. Another is that there are general problems about the ethics of violence, no matter who carries it out and what their reasons might be. The ethics of war between states is a subset of these broader issues. Nonetheless, when I speak of the ethics of war, I generally assume that the principles that are relevant to war apply to organized violence by governments and non-governmental groups alike, including the groups usually identified as terrorists.