I would like to thank Dr Guglielmo Verdirame for his invaluable comments and guidance. My gratitude is also owed to Tobias Schaffner and an anonymous CJLJ reviewer for comments on earlier drafts of this article.

1. International humanitarian law (also called the ‘law of armed conflict’ or, more colloquially, the ‘law of war’) is the body of international treaties and customary law which govern the conduct of hostilities on the battlefield, and related issues. Most important for our purposes is the Protocol Additional to the Geneva Conventions of the 12 August 1949, and relating to the Protection of Victims of International Armed Conficts (Protocol 1), 8 June 1977, 1125 UNTS 3, (entered into force 7 December 1979) [API], which provides rules for what or who may be targeted and with how much force.

2. “Proportionality” is a term familiar to military lawyers, as I will shortly explain. I will not draw a distinction between necessity and proportionality—in IHL, a disproportionate attack is considered unnecessary and vice versa.

3. For the purposes of this essay, I include civilians directly participating in hostilities in the term “combatant”, because although they are subject to different rules in some aspects of IHL (such as upon capture), they are subject to the same general targeting principles.

4. It is a curious fact that nowhere in the treaties of IHL is the right to kill combatants expressly mentioned. It can only be inferred indirectly from API. Art 48 provides the “Basic rule” that military operations shall only be directed against “military objectives”. However, API conspicuously avoids defining combatants as “military objectives”, and in Art 52(2) only gives a definition of military “objects”. Of course, nevertheless, the right to kill combatants is considered long-standing customary law.

5. The jus in bello (‘law in war’) refers to IHL, i.e., the law applicable to conduct on the battlefield. The jus ad bellum (‘law of war’) is only applicable to states. It dictates the justifable causes of war and is largely found in the Charter of the United Nations (26 June 1945, Can TS 1945 No 7). It is now typically called the law on the “use of force”. See generally Gray, Christine, International Law and the Use of Force, 3d ed (New York: Oxford University Press, 2008).Google Scholar

6. API, supra note 1 at Art 51(5)(b).

7. Ibid at Art 41(2).

8. 19 December 1966, 999 UNTS 171, (entered into force 23 March 1976) [emphasis added].

9. European Convention for the Protection of Human Rights and Fundamental Freedoms, 4 November 1950, ETS 5, (entry into force 3 September 1953). See generally Sassòli, Marco and Olson, Laura M, “The relationship between international humanitarian law and human rights law where it matters: admissible killing and internment of fighters in non-international armed conficts” (2008) 90 Int’l Rev Red Cross 599 at 610CrossRefGoogle Scholar.

10. Adopted by the Eighth United Nations congress on the Prevention of Crime and the Treatment of Offenders, 27 August to 7 September 1990 at Art 10.

11. See Droege, Cordula, “Elective affinities? Human Rights and Humanitarian Law” (2008) 90 Int’l Rev Red Cross 501 at 503-07CrossRefGoogle Scholar.

12. Legality of the Threat or Use of Nuclear Weapons Case, Advisory Opinion, [1996] ICJ Rep 226 at para 25Google Scholar.

13. Schabas, William A, “Lex Specialis? Belt and Suspenders? The Parallel Operation of Human Rights Law and the Law of Armed Conflict, and the Conundrum of Jus Ad Bellum “ (2007) 40 Israel L Rev 592 at 598CrossRefGoogle Scholar.

14. See, e.g., Lubell, Noam, “Challenges in Applying Human Rights Law to Armed Conflict” (2005) 87 Int’l Rev Red Cross 737 at 737-38CrossRefGoogle Scholar.

15. Sassòli, supra note 9 at 603.

16. See generally Melzer, Nils, Targeted Killing in International Law (New York: Oxford University Press, 2008).CrossRefGoogle Scholar

17. Sandoz, Yves, Swinarski, Christophe & Zimmerman, Bruno, eds, Commentary on the Additional Protocols of 8 June 1977 to the Geneva Conventions of 12 August 1949 (Geneva: Martinus Nijhoff, 1987) at para 1612Google Scholar.

18. Ibid at para 1630.

19. Ibid at para 1614.

20. International Committee of the Red Cross, Customary International Humanitarian Law, Volume I: Rules, ed by Henckaerts, Jean-Marie & Doswald-Beck, Louise (Cambridge: Cambridge University Press, 2005) at 166–70 CrossRefGoogle Scholar.

21. Doswald-Beck, Louise, “The Right to Life in Armed Conflict: Does International Humanitarian Law Provide all the Answers?” (2006) 88 Int’l Rev Red Cross 881 at 900CrossRefGoogle Scholar.

22. Canada, Office of the Judge Advocate General, Law of Armed Conflict at the Operational & Tactical Levels, (Ottawa, 13 August 2001) at 6-3 and 7-3Google Scholar(publication document B-GJ-005-104/FP021) [emphasis added]. See ICRC, supra note 20, Volume 2 at 941-72.

23. Melzer, Nils, Interpretive Guidance on the Notion of Direct Participation in Hostilities Under International Humanitarian Law (Geneva: ICRC Reference Materials, 2009) at Section IX, p 77 Google Scholar.

24. Melzer also argues in a separate article that the same result may be achieved by reference to the maux superfus principle reflected in Art 35(2) of API. However, as even he admits, this provision is understood to refer to the use of particular types of unlawful weapons and not as embodying a general requirement limiting the use of force against combatants using conventional weapons. See Melzer, Nils, “Targeted Killing or Less Harmful Means?—Israel’s High Court Judgment on Targeted Killing and the Restrictive Function of Military Necessity” (2006) 9 YB Int’l Human L 87 at 96-97Google Scholar.

25. Melzer, supra note 23 at 79.

26. Ibid at 82.

27. See ibid at n 212, noting that this topic was “highly controversial” in the meetings of the group of experts. See generally Parks, W Hays, “Part IX of the ICRC ‘Direct Participation in Hostilities’ Study: No Mandate, No Expertise, and Legally Incorrect” (2010) 42 Int’l Law & Politics 769 at 783-85 and 793-96Google Scholar.

28. Doswald-Beck, supra note 21 at 902-03.

29. See Parks, supra note 27.

30. Milanovic, Marko, “Lessons for Human Rights and Humanitarian Law in the War on Terror: Comparing Hamdan and the Israeli Targeted Killings Case” (2007) 89 Int’l Rev Red Cross 373 at 391Google Scholar. See also Blum, Gabriella, “The Dispensable Lives of Soldiers” (2010) 2(1) J Legal Analysis 115 at 126CrossRefGoogle Scholar.

31. See, e.g., Parks, supra note 27. Parks, a lawyer for the U.S. Department of Defense, offers a 62 page critique of the ICRC’s legal acumen, while devoting only a cursory section to the question of whether imposing a legal limit on killing active combatants is actually a good idea.

32. (Oxford: Oxford University Press, 2006).

33. Ibid at 136.

34. Constant, Benjamin, The Liberty of the Ancients Compared with that of the Moderns (1819), available at: http://mises.org/daily/2524.Google Scholar

35. Weil, Simone, “Hitler and Roman Foreign Policy”, translated and ed by Rees, Richard, Selected Essays, 1934-1943 (London: Oxford University Press, 1962) 116.Google Scholar

36. The Rights of War and Peace: Political Thought and the International Order from Grotius to Kant (Oxford: Oxford University Press, 1999) at 229.Google Scholar

37. Augustine, , On Free Choice of the Will, translated by Williams, Thomas (Indianapolis, IN: Hackett, 1993) at Book I, Q9Google Scholar. See also Tuck, supra note 36 at 56.

38. Augustine, Contra Faustum, at Book XXII, para 75, available at: http://www.gnosis.org/li-brary/contf2.htm. The exception is where the unjustness of the war is so glaringly obvious that the soldier should shirk his duty.

39. Gratian, , Decretum Gratiani, Q5 as excerpted in Reichberg, Gregory M, Syse, Henrik & Begby, Endre, eds, The Ethics of War: Classic and Contemporary Readings (Malden, MA: Blackwell, 2006) at 119 [Ethics]Google Scholar.

40. This is the principle which inter alia justifes the collateral killing of civilians in war. If the primary intention is to attack a military target, and this cannot be done without killing a certain proportional number of civilians, then according to the principle of double effect the second consequence of the action (the death of civilians), although unjust, does not prohibit the action because the primary intention or effect (the destruction of a military target) is justified.

41. Thomas Aquinas, Summa Theologiae, II-II, q 64, a 7, as excerpted in Ethics, supra note 39 at 190.

42. Ibid at 191.

43. Tuck, Richard, “Democracy and Terrorism” in Bourke, Richard & Geuss, Raymond, eds, Political Judgement: Essays for John Dunn (New York: Cambridge University Press, 2009) 313 at 322CrossRefGoogle Scholar.

44. On the Law of War, QI, Art. 4, V.I as excerpted in Ethics, supra note 39 at 315.

45. Francisco Suárez, Metaphysical Disputations, XIII (De bello), VII as excerpted in Ethics, supra note 39 at 363-64.

46. Ibid at VII.6 at 362.

47. Ibid at IV.3 at 348.

48. Vitoria, Francisco de, De indis et de iure belli reflectiones, translation by Bate, John Pawley, ed by Nys, Ernest (Washington, DC: The Carnegie Institute of Washington, 1917) at 182.Google Scholar

49. Ibid.

50. See Kennedy, David, “Primitive Legal Scholarship” (1986) 27 Harv Int’l LJ 1 Google Scholar.

51. Best, Geoffrey, Humanity in Warfare: The Modern History of the International Law of Armed Conficts (New York: Columbia University Press, 1980) at 40.Google Scholar

52. Hegel, GWF, Philosophy of Right, translated by Knox, TM (Oxford: Oxford University Press, 1967 [1952]) at s 337 Google Scholar.

53. Ibid at s 324.

54. Ibid.

55. Rousseau, Jean-Jacques, The Social Contract, in The Social Contract and other Later Political Writings , translated and ed by Gourevitch, Victor, (Cambridge: Cambridge University Press, 1997) at 46–47 Google Scholar.

56. See, e.g., Berman, Nathaniel, “Privileging Combat? Contemporary Conflict and the Legal Construction of War” (2004) 43 Colum J Transnat’l L 1 at 9Google Scholar.

57. Rousseau, supra note 55 at 46-47.

58. Rousseau, Jean-Jacques, “The State of War” in Reading Rousseau in the Nuclear Age , translated by Roosevelt, Grace, (Philadelphia, PA: Temple University Press, 1990) at 197.Google Scholar

59. Ibid at 185.

60. Ibid at 191.

61. Ibid.

62. “Summary of the Abbé de Saint-Pierre’s Project for Perpetual Peace” in Roosevelt, supra note 58 at 200.

63. Rousseau, supra note 58 at 189.

64. Rousseau did hint at having formulated such a theory, but apparently the essay explaining it was, tragically, destroyed. See Tuck, supra note 36 at 205-07.

65. Vattel in fact based his writings largely on Wolff, and is therefore sometimes said to have been unfairly credited as a great innovator. See Ruddy, FS, “The Acceptance of Vattel” in Alexandrowicz, CH, ed, Grotian Society Papers 1972 (The Hague, Geneva: Martinus Nijhoff, 1972) 177.Google Scholar

66. Vattel, Emerich de, The Law of Nations or the Principles of Natural Law, translated by Fenwick, Charles G (Legal Classics Library, 1916) at 259 Google Scholar. This mirrors very closely a similar passage from Wolff: Wolff, Christian, Jus gentium methodo scientifca pertractatum, translated by Drake, Joseph H (Oxford: Clarendon Press, 1934) at 373.Google Scholar

67. Vattel, ibid at 259. See similarly Wolff, ibid at 374.

68. Vattel, supra note 66 at 238.

69. Ibid at 289-90.

70. Wolff, supra note 66 at 9.

71. See ibid at 139.

72. Ibid at 409.

73. Ibid.

74. See infra note 125 and accompanying text.

75. Wolff, supra note 66 at 410.

76. Grotius, Hugo, De jure belli ac pacis libri tres, translated by Kelsey, Francis W (Washington, DC: Carnegie Institute of Washington, 1925) at 741.Google Scholar

77. Ibid at 628. Grotius also believed that even an individual’s property could not, conceptually speaking, be liable for the acts of the state, for “[b]y the strict law of nature no one is bound by another’s act” (at 634).

78. Ibid at 733.

79. Ibid at 58.

80. Ibid at 172.

81. Ibid at 172.

82. Ibid at 173.

83. Meron, Theodor, “The Humanization of Humanitarian Law” (2000) 94 Am J Int’l L 239 CrossRefGoogle Scholar.

84. Cohen, Jean L, “Sovereignty in the Context of Globalization: A Constitutional Pluralist Perspective” in Besson, Samantha & Tasioulas, John, eds, The Philosophy of International Law (Oxford: Oxford University Press, 2010) 261 at 264Google Scholar.

85. Memory of Solferino ,> translated by American National Red Cross (Geneva: ICRC Publications, 1986).+translated+by+American+National+Red+Cross+(Geneva:+ICRC+Publications,+1986).>Google Scholar

86. Convention (IV) respecting the Laws and Customs of War on Land and its annex, 18 October 1907, (entry into force 26 January 1910). Available at: http://www.icrc.org/ihl.nsf/FULL/195?Open document.

87. Furthermore, the first rhetorical references to “rights” and “entitle[ments]” inspired by human rights law can be found in the Geneva Conventions and Protocols. See Greenwood, Christopher, “Rights at the Frontier” in Rider, Barry, ed, Law at the Centre: the Institute of Advanced Legal Studies at Fifty (Dordrecht, The Netherlands: Kluwer Law International, 1999) 277 at 382-83Google Scholar.

88. Provost, René, International Human Rights and Humanitarian Law (Cambridge: Cambridge University Press, 2002) at 47.CrossRefGoogle Scholar Only the victim state may demand compensation: API, supra note 1 at Art 91.

89. Provost, supra note 88 at 34.

90. Meron, supra note 83 at 245-47.

91. Annan, Kof, “Two Concepts of Sovereignty”, The Economist (18 Sept 1999) at 49–50 Google Scholar.

92. Convention (II) with Respect to the Laws and Customs of War on Land and its annex, 29 July 1899, (entry into force 04 September 1900) [emphasis added]. Available at: http://www.icrc. org/ihl.nsf/FULL/150?Open document.

93. Geneva Convention for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field (First Geneva Convention), 12 August 1949, 75 UNTS 31, (entry into force 21 October 1950) at Art 63; Geneva Convention for the Amelioration of the Condition of the Wounded, Sick and Shipwrecked Members of the Armed Forces at Sea (Second Geneva Convention), 12 August 1949, 75 UNTS 85, (entry into force 21 October 1950) at Art 62; Geneva Convention Relative to the Protection of Civilian Persons in the Time of War (Fourth Geneva Convention), 12 August 1949, 75 UNTS 287, (entry into force 21 October 1950) at Art 158.

94. Supra note 1 at Art 1(2).

95. See, e.g., McMahan, Jeff, Killing in War (Oxford: Oxford University Press, 2009)CrossRefGoogle Scholar; Norman, Richard J, Ethics, Killing and War (Cambridge: Cambridge University Press, 1995).CrossRefGoogle Scholar

96. Nagel, Thomas, “War and Massacre” (1972) 1 Phil & Pub Affairs 123 at 138Google Scholar.

97. Walzer, Michael, Just and Unjust Wars (New York: Basic Books, 1980) at 146.Google Scholar

98. Kenny, Anthony, The Logic of Deterrence (London: Firethorn Press, 1985) at 10.Google Scholar

99. McMahan for instance makes a distinction between deserving a harm as an end in itself (e.g., punishment as retribution) and being liable to a harm (e.g., where that harm serves some further purpose). See McMahan, supra note 95 at 8.

100. Grotius, supra note 76 at 172.

101. Nagel, supra note 96 at 133-8.

102. Ibid at 138.

103. Ibid at 139.

104. Norman, supra note 95 at 176.

105. Paskins, Barrie & Dockrill, Michael, The Ethics of War (London: Duckworth, 1979) at 224.Google Scholar

106. Ibid at 225.

107. Norman, supra note 95 at 188.

108. “Fifty Years after Hiroshima” in John Rawls: Collected Papers, ed by Freeman, Samuel (Cambridge, MA: Harvard University Press, 1999) 565 as excerpted in Ethics, supra note 39 at 635Google Scholar.

109. In the interests of concision, I have left aside a less important philosophical issue which is the now outdated notion of “assassinations.” Assassinations are ‘treacherous killings’, which are variously described in the tomes of Alberico Gentili, Grotius, Vattel and others as ‘dishonourable’ tactics which betray notions of ‘valour’ and ‘chivalry’ by using surprise or deceit to attack defenceless enemies. However, the norm against assassinations is considered completely inoperative today, given that routine feature of modern warfare: the use of ranged weapons such as airstrikes, missiles and sniper rifles to attack (often) totally defenceless combatants. However laudable sentiments of ‘valour’ may be, they do not serve as a stable foundation for preventing unnecessary death. The rules on killing must be grounded in a respect for the humanity of the victim, not the killer’s honour. The latter can admit of too many exceptions and is vulnerable to vague and ever-changing norms in warrior culture, just as the advent of airstrikes and missiles has made the norm on assassinations inoperative today.

110. Mavrodes, George, “Conventions and the Morality of War” (1975) 4 Phil & Pub Affairs 117 Google Scholar.

111. Azar Gat demonstrates that in the anarchy of pre-state societies, roughly 15 percent of adults could be expected to die at the hands of other humans. By contrast, even during WW2, only about 3 percent of both the French and German populations perished (Gat, supra note 32 at 131-32).

112. Albert de Lapradelle, for instance, admonishes Grotius for remaining “in a state of barbarism” as compared to the enlightened Vattel (“Introduction” in Vattel, supra note 66 at xlviii).

113. Supra note 76 at 641-57.

114. Ibid at 716.

115. See, e.g., Tadashi, Tanaka, “Grotius’s Concept of Law” in Yasuaki, Onuma, ed, A Normative Approach to War: Peace, War, and Justice in Hugo Grotius (Oxford: Clarendon Press, 1993).Google Scholar

116. Tuck, supra note 36 at 326.

117. For instance, he writes that property rights are considered, “by a certain necessity”, surrendered to the state “because otherwise a great licence to cause injury would arise. The reason is that in many cases the goods of rulers cannot so easily be seized as those of private persons, who are more numerous.” Thus more violence would result by foreign claimants trying to fight their way to the ruler’s property. This surrender of rights is one of those rules “established by civilized nations in response to the demands of usage and human needs.” Grotius, supra note 76 at 624.

118. Another reason may be that Grotius did not want to alienate the sovereigns of Europe who were his intended audience by labeling them all as war criminals. Europe had just emerged from the Thirty Years’ War, in which Grotius saw “a lack of restraint in relation to war, such as even barbarous races should be ashamed of” (ibid at 20). Grotius conceded that they had not departed from customary practice, but advised a more just approach going forward. Grotius’ eagerness to appease authority is demonstrated somewhat uncomfortably in the flowery and absurd dedication to King Louis XIII. (Ibid at iii) On the historical context in which Grotius was writing, see also Ruddy, supra note 65 at 181.

119. Best, supra note 51 at 286.

120. Keegan, John, The Face of Battle (New York: Viking Press, 1976) at 47.Google Scholar

121. Clausewitz, Carl von, On War, translated by Howard, Michael (Princeton, NJ: Princeton University Press, 1976) at ch 3Google Scholar, as excerpted in Ethics, supra note 39 at 560-61.

122. Grotius, , Selections of Grotius’ De jure Belli ac Pacis, translated by WSM|Knight (Grotius Society Publications, 1922), vol 3 at 35Google Scholar.

123. The Lieber Code was drafted by Francis Lieber, at the behest of Abraham Lincoln, for the Union army during the US Civil War. See Doswald-Beck, Louise et al, “International Humanitarian Law and Human Rights Law” (1993) 293 Int’l Rev Red Cross 94 at 105CrossRefGoogle Scholar.

124. API, supra note 1 at Art 41(2).

125. Vattel, supra note 66 at 295.

126. Marshall, SLA, Men Against Fire (Norman: University of Oklahoma Press, 2000).Google Scholar

127. Ibid at 56.

128. Ibid at 79.

129. Grossman, Dave, On Killing: The Psychological Cost of Learning to Kill in War and Society (Boston, MA: Little, Brown and Company, 1996) at 35.Google Scholar

130. Lord Tennyson, Alfred, “The Charge of the Light Brigade” (1854)Google Scholar.

131. Kennedy, David, Of War and Law (Princeton, NJ: Princeton University Press, 2006) at 103.Google Scholar

132. French, Shannon E, The Code of the Warrior, Exploring Warrior Values Past and Present (Lanham, MD: Rowman & Littlefeld, 2003) at 10.Google Scholar

133. Parks, supra note 27 at 810.

134. McCann v United Kingdom (1995), 324 ECHR (Ser A) paras 200-205. UK police were found to have justifiably fired upon IRA members because they genuinely thought the IRA were about to detonate a bomb. However, the Court nevertheless found a violation of the right to life since earlier in the same day the UK had not taken advantage of an opportunity to arrest the suspected terrorists. Thus, even if the specific instance of killing was justified, the police were under an obligation to have pursued available non-lethal alternatives. In war, it seems unrealistic to impose an obligation to, for example, arrest enemy soldiers when the opportunity presents itself, rather than wait to engage them in combat the next day. Resources may be thin, and strategy and tactics may demand otherwise.

135. See Doswald-Beck, supra note 21 at 887.

136. See generally Extraterritorial Application of Human Rights Treaties, ed by Coomans, Fons & Kamminga, Menno T (Oxford: Intersentia, 2004).Google Scholar

137. See Verdirame, Guglielmo, “Human Rights in War: A Framework for Analysis” (2008) 6 Eur HRL Rev 689 at 693Google Scholar, for the proposition that a “human rights compliant war is impossible” but international humanitarian law is always, by design, attainable.

138. Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v Uganda), Judgment, [2005] ICJ Rep 168 at para 178Google Scholar.

139. Development and Principles of International Humanitarian Law (Geneva: Martinus Nijhoff, 1985) at 75.Google Scholar

140. Solis, Gary D, The Law of Armed Conflict: International Humanitarian Law in War (Cambridge: Cambridge University Press, 2010) at 280–82.CrossRefGoogle Scholar

141. Though, depending on how high up the chain of command they are, the decisions of such commanders may bear on the issue of state responsibility.

142. See supra note 23 at 80.

143. Anscombe, GEM, “War and Murder” in Stein, Walter, ed, Nuclear Weapons: A Catholic Response (New York: Sheed & Ward, 1961) at 59.Google Scholar

144. See, e.g., API, supra note 1 at Art 85(1).

145. Rome Statute of the International Criminal Court, 17 July 1998, UNTS Vol 2187 (entry into force 1 July 2002) at Art 8(2)(a).

146. API supra note 1 at Art 87.

147. Ibid at Art 85(3)(e).

148. Ibid at Art 85(3) [emphasis added].

149. United States of America, Instructions for the Government of Armies of the United States in the Field, prepared by Lieber, Francis, (Washington, DC: Government Printing Office, 1989)Google Scholar at Art 29 [The Lieber Code].

150. Ibid at Art 15.

151. Best, supra note 51 at 10.

152. Ibid at 165.