1 I shall usually use the designation IHL. Other widely employed names for the same body of law include the law of armed conflict and the laws of war. Many writers refer to these laws as part of the jus in bello, at least some under the mistaken impression that this nineteenth-century coinage reflects a fundamental medieval dichotomy – for the modern origins of this pretentious Latin jargon, see R. Kolb, ‘Origin of the Twin Terms Jus ad Bellum/Jus in Bello’, (1997) IRRC 320, at 553–62.

2 This issue has recently been debated in two opposing pairs of articles: McMahan, J., ‘The Morality of War and the Law of War’, in Rodin, D. and Shue, H. (eds.), Just and Unjust Warriors: The Moral and Legal Status of Soldiers (2008), 19Google Scholar; H. Shue, ‘Do We Need a “Morality of War?”’, in ibid., 87; and McMahan, J., ‘Laws of War’, in Besson, S. and Tasioulas, J. (eds.), The Philosophy of International Law (2010), 493Google Scholar; and H. Shue, ‘Laws of War’, in ibid., 511. A critique of both sides in that debate appears in Rodin, D., ‘Morality and Law in War’, in Strachan, H. and Scheipers, S. (eds.), The Changing Character of War (2011), 446CrossRefGoogle Scholar; subsection 2.3 below is a response to Rodin.

3 Naturally, more than two requirements hold. A provocative discussion of other possible requirements, and the status to attribute to them, is in Davidovic, J., ‘The International Rule-of-Law and Killing in War’, (2012) 38 Social Theory and Practice, 531–52CrossRefGoogle Scholar.

4 I emphasized this in Shue, ‘Do We Need a “Morality of War”?’, supra note 2, 91.

5 The most abstract statements of the fundamental principles may not differ across arenas, but we are interested in the concrete specifications of what to do that can be action-guiding.

6 Where an exception is allowed, it is specified in advance. ‘There can be no appeal to military necessity outside the rules’ – Hampson, F., ‘The Principle of Proportionality in the Law of Armed Conflict’, in Perrigo, S. and Whitman, J. (eds.), The Geneva Conventions under Assault (2010), 42Google Scholar at 43.

7 Indeed, W. J. Talbott has made the tantalizing argument that the need for exceptions is the engine of moral progress over history – see Human Rights and Human Well-Being (2010), 103–29.

8 Needless to say, there is in fact much violence in domestic life. Many people in domestic life – for example, racially persecuted minorities – do not in fact benefit from the promised rule of law. In many societies women benefit very unequally. I am here comparing rules with rules – what might be thought of as ideal behaviour in peaceful domestic life with ideal behaviour in combat. I am not comparing rules in the one case with behaviour in the other, or behaviour with behaviour, at this point. I am grateful to Seth Lazar for discussion on this point.

9 To the extent to which the International Criminal Court and other elements of evolving international criminal law take firm hold, the differences between peaceful domestic and wartime international situations may be reduced. Reducing them – that is, solidifying the international rule of law – is a worthy, if not noble, goal. For thoughtful reflections, see Krisch, N., Beyond Constitutionalism: The Pluralist Structure of Postnational Law (2011).Google Scholar

10 Much of what will be said is true of civil war as well as international war, and often whether a conflict is civil or transnational is one of the points at dispute in the fighting. There are also international laws concerning non-international conflicts, for example, the 1977 Geneva Protocol II. Nevertheless, I am thinking mainly of laws for international war. Some complications must be left aside, and while it is often important to recognize messy middle cases, it is more vital right now to appreciate how far apart from each other are the two extremes of international war and peaceful domestic life. On the general importance of attending to the messiness, see Coady, C. A. J., Messy Morality: The Challenge of Politics (2008).Google Scholar

11 See Rodin, D., ‘The Ethics of Asymmetric War’, in Sorabji, R. and Rodin, D. (eds.), The Ethics of War: Shared Problems in Different Traditions (2006), 153–68Google Scholar; and J. McMahan, Killing in War (2009). For further explanation of why philosophical approaches resting on individual moral liability to be killed are neither useful nor necessary for arriving at morally justified action-guiding rules for war, see Dill, J. and Shue, H., ‘Limiting the Killing in War: Military Necessity and the St. Petersburg Assumption’, (2012) 26 Ethics & International Affairs, 311–33CrossRefGoogle Scholar. The way that conflicts are generally fought is another reason why one ought to think long and hard in advance about whether one's participation in a particular conflict will be justified.

12 And even what counts as direct participation is sometimes obscure – see text to infra note 15.

13 As wars tend to be fought now, many fighters are young, inexperienced generally, and inexperienced specifically in making moral assessments in unfamiliar circumstances where often they do not even speak the language of their adversaries, and many soldiers have only minimal education (although some officers have considerably more). Both these factors could, however, in principle be eliminated by using older and better-educated fighters.

14 For further explanation of the poverty of morally relevant information and lack of opportunity for moral reflection in the circumstances of combat, see Shue, ‘Do We Need a “Morality of War?”’ and ‘Laws of War’, supra note 2. Soldiers are, of course, not constantly in combat. In other circumstances they have more opportunity for reflection, but will still lack information about individuals whom they will confront when they return to combat. One cannot be morally required, even in so-called ‘ideal theory’, to do what it is in fact impossible to do.

15 Those combatants who disguise themselves as civilians while fighting, such as suicide bombers who approach guards at checkpoints with their weapon not visible, are of course treacherously exploiting this very fact.

16 G. Best, War and Law since 1945 (1994), 262.

17 [Gen.] Rogers, A. P. V., Law on the Battlefield (2004), 9.Google Scholar

18 1907 Hague Regulations Respecting the Laws and Customs of War on Land, Annexed to Hague Convention (II) of 1899 and Hague Convention (IV) of 1907, Art. 1, in Roberts, A. and Guelff, R. (eds.), Documents on the Laws of War (2000), 73.Google Scholar

19 1977 Geneva Protocol I, Art. 44(3), 1125 UNTS (1979), 3. The United States rejects this change, which is one of its primary reasons for refusing to ratify the Protocol. Notoriously, many terrorists refuse to comply with even the newer weaker requirement in order to remain covert until they strike, which is the main reason they do not qualify for the status of combatant or, if captured alive, the privileges of prisoners of war. This is not the place at which to take up these definitional disputes, which are not central to the more general thesis here.

20 M. Herr, Dispatches (1978), 135. Thanks to Seth Lazar for calling my attention to this passage – for fuller analysis, see Lazar, S., ‘The Responsibility Dilemma for Killing in War: A Review Essay’, (2010) 38 Philosophy & Public Affairs 180CrossRefGoogle Scholar, at 211.

21 Also see Shue, ‘Do We Need a “Morality of War”?’, supra note 2; Shue, ‘Laws of War’, supra note 2, and S. Lazar, ‘The Responsibility Dilemma’, supra note 20, 180.

22 1880 Oxford Manual, Preamble – the phrases are there attributed to ‘Baron Jomini’ (Antoine-Henri, Baron de Jomini, author of Treatise on Grand Military Operations (1865) and of Summary of the Art of War (1868)). I have elaborated on the laws of war as limitations, not prohibitions, in Shue, ‘Laws of War’, supra note 2.

23 Obviously one possibility is that some moral commitments can be fully honoured during war while others cannot be honoured at all. Another is that some commitments can be honoured only partially. And a third is a mixture of the first two.

24 Some lawyers would understand this as the requirement of generality – see, for example, Brunnée, J. and Toope, S., Legitimacy and Legality in International Law: An Interactional Account (2010), 279CrossRefGoogle Scholar; more generally, see A. Roberts, ‘The Principle of Equal Application of the Laws of War’, in Rodin and Shue, supra note 2, 226–54. For critiques, see McMahan, supra note 11; the chapters by McMahan and Rodin in Rodin and Shue, supra note 2 and Rodin, ‘Morality and Law in War’, in Strachan and Scheipers, supra note 2. A deep error made by Michael Walzer in his monumental work, Just and Unjust Wars, is to assume that whether it can be morally justified for the laws to be the same for all fighters depends on the moral status of individual fighters; Jeff McMahan has carried this assumption into Killing in War. Walzer argued that the laws can be the same on moral grounds, since individual fighters on opposing sides are morally equal; McMahan subsequently argued that the laws can be the same only if they are mere conventions because fighters on opposing sides are not morally equal – see Dill and Shue, ‘Limiting the Killing in War’, supra note 11, for the argument that both Walzer and McMahan are incorrect in their respective ways for the same underlying reason. I am trying here to sketch a third position that rests on a different account of how laws for the conduct of war can be morally justified.

25 M. Bothe, K. J. Partsch, and W. A. Solf, New Rules for Victims of Armed Conflicts: Commentary on the Two 1977 Protocols Additional to the Geneva Conventions of 1949 (1982), at 32.

26 D. Rodin, ‘The Moral Inequality of Soldiers: Why Jus in Bello Asymmetry Is Half Right’, in Rodin and Shue, supra note 2, 44–68, at 44. Rodin himself rejects the symmetry thesis.

27 See (ICJ Judge) Greenwood, C., ‘Historical Development and Legal Basis’, in Fleck, D. (ed.), The Handbook of International Humanitarian Law (2008), 37Google Scholar: ‘A state may use only such force (not otherwise prohibited by humanitarian law) as is necessary to achieve the goals permitted by the right of self-defence. In that sense, the ius ad bellum has an effect upon the conduct of hostilities as well as upon the initial right to resort to force.’

28 And they should not even be allowed to do everything that it would be helpful to do in defending oneself, but we shall come to this later.

29 And many non-state actors also claim the prerogative of using violence to attain their goals.

30 Presumably the mistake sometimes is, and sometimes is not, excusable, and one must judge case by case.

31 Nuremberg might be viewed as having taken a tiny step in this direction by convicting people of crimes against peace, but that was of course ex post punishment, not ex ante prevention, and those were extreme cases.

32 Strictly speaking, the Security Council has the authority to judge definitively whether a state is guilty of an improper threat or use of force, but since the veto-wielding permanent members and the clients they shield are effectively immune to control by the Security Council, the authority fails to be universal in reality. Many argue that, in consequence, the rules are not de facto the same for all. This is an extremely important issue, but I cannot take it up here. The point here is that in principle they are supposed to be the same for all, and for good reasons.

33 For that reason I do not expect it to happen, irrespective of whether it ought to happen. But nothing in the argument depends on the current situation being unchangeable on this point. We do not now have an institution with the recognized authority to tell every state that it may not go to war because its war would not be justified, and it is not in prospect. If that were to change, it would be a historic development.

34 If the practice of war can be changed, the rules applicable to the practice can be changed. But the international law cannot be radically divergent from state practice, so the international law cannot be changed first.

35 Rodin, supra note 2, 458–9.

36 Ibid., 458.

37 Shue, ‘Do We Need a “Morality of War”?’, supra note 2, 90.

38 Ibid., 452.

39 Rodin's analysis of proportionality is in Rodin, supra note 26, 53–4. Mine is: H. Shue, “Proportionality in War”, in G. Martel (ed.), The Encyclopedia of War (2012) s.v. “Proportionality in War”.

40 The extent to which this is true is an empirical question to be investigated. Other factors that are not equal between two cases may of course pull in the other direction.

41 Dinstein, Y., The Conduct of Hostilities under the Law of International Armed Conflict (2010)CrossRefGoogle Scholar is a notable example. The significance of this was first made vividly clear to me by Janina Dill – see ‘The Definition of a Legitimate Target in US Air Warfare: A Normative Enquiry into the Effectiveness of International Law in Regulating Combat Operations’ (D.Phil., Oxon. thesis, 2012).

42 In some wars a stalemate constitutes success for at least one side, for example.

43 And since the Second World War and, most pointedly, the bombings of Dresden, Hamburg, Tokyo, Hiroshima, and Nagasaki, never again to allow such a descent into total war.

44 War has no unchanging essence. It is a human practice – we are, after all, discussing its rules. And human practices can evolve; that is, either decline or progress. Elaine Scarry has an imaginative exploration of alternative contests that one might think could substitute for war, although she reluctantly emphasizes the difficulty of replacing the breaking of human bodies with any other activity that would produce the same psychological and political result; see Scarry, E., The Body in Pain: The Making and Unmaking of the World (1985), 91–139.Google Scholar

45 I have discussed military necessity more fully in Dill and Shue, supra note 11.

46 So this is most definitely not a ‘right to a fighting chance’ for all parties of the kind suggested by Michael Gross – see discussion in section 4 below.

47 I am grateful to Janina Dill for raising this issue.

48 Space is not available to document this at any length, although I think it is obvious in any case. But, for example, the 1868 St Petersburg Declaration, which is one of the wellsprings of IHL, sent out the reverberating cry ‘that the only legitimate object which States should endeavour to accomplish during war is to weaken the military forces of the enemy’ – 1868 St Petersburg Declaration, Preamble, in Roberts and Guelff, supra note 18, at 55 – and the 1977 Protocol I, which is the most important single expression of contemporary IHL, presents as an exceptionless ‘basic rule’ that ‘the Parties to the conflict shall at all times distinguish between the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives’ – 1977 Protocol I, Art. 48, in ibid., at 447.

49 Legality of the Threat or Use of Nuclear Weapons (Nuclear Weapons Case), Advisory Opinion, Opinion of 8 July 1996, [1996] ICJ Rep. 226, at 257, para. 79.

50 The shock-value of these killings depends upon the fact that most people believe them to be immoral. The effectiveness of the tactic is parasitic upon the acceptance by its intended audience of the norm prohibiting the practice.

51 Advocates of some more moderate compromise would need to formulate their alternative principles precisely enough that they did not degenerate into my illustrative ones.

52 Gross, M., Moral Dilemmas of Modern War: Torture, Assassination, and Blackmail in an Age of Asymmetric Conflict (2010), 39Google Scholar. I am grateful to Marco Meyer for discussion of these arguments. Also see the review of Gross by C. A. J. Coady, (2011) 25 Ethics & International Affairs, 90.

53 Gross, supra note 52, at 38.

54 Ibid., 38–9.

55 And guaranteeing that the sides were even would be a formula for prolonging every war to the maximum duration because it would take longer for either side to establish military superiority through the fighting. This mistake was made in the Bosnia war, which dragged on for years in a murderous stalemate thanks in part to a misguided NATO commitment to impartiality.

56 Does this include the right to start a war? Or only to win it if someone else starts it?

57 For a sophisticated analysis of reciprocity at the international level, see M. Osiel, The End of Reciprocity: Terror, Torture, and the Law of War (2009). Osiel fruitfully distinguishes three types of reciprocity, including ‘diffuse or systemic reciprocity’, at 368.

58 1977 Geneva Protocol I, Art. 35(1). This rock-bottom principle is articulated in many sources: the 1874 Brussels Declaration, the 1880 Oxford Manual, the 1899 and 1907 Hague Regulations, the Preambles to the 1980 Convention on Certain Conventional Weapons, and the 1997 Ottawa Convention on Anti-Personnel Mines – see Roberts and Guelff, supra note 18, at 9.

59 In rare cases we ought to assist them militarily, i.e. a humanitarian intervention is called for. People can be driven to extreme measures because others do not provide them the help they ought to receive. Acknowledging that a group has a just cause will in some cases entail a duty for others to assist them, but it will never entitle them to brutalize civilians. See Shue, H., ‘Limiting Sovereignty’, in Welsh, J. (ed.), Humanitarian Intervention and International Relations (2004), 11–28Google Scholar and 189–91.

60 F. Nietzsche, Beyond Good and Evil: Prelude to a Philosophy of the Future (1966), at 89 (‘Epigrams and Interludes’, 146).