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Proportionality is a core principle in international law, which provides that the legality of an action shall be determined depending on the respect of the balance between the objective and the means and methods used as well as the consequences of the action. This principle implies an obligation to appreciate the context before deciding on the legality or the illegality of an action. This assessment is the responsibility of those who act. In case of dispute or doubt, tribunals can assess the facts and their legality a posteriori.
Proportionality is particularly important to balance the argument of military necessity in assessing the legality of the use of armed force. Particularly, it applies in cases of individual or collective self-defense, in cases of recourse to armed force by a State to restore order and public safety in times of internal disturbances, and in situations of international or non-international conflicts.
International criminal law also provides that sanctions must be proportionate to the gravity of the crime.
Proportionality in Attacks and Retaliation
International law does not authorize States to resort to armed force except in cases of self-defense or aggression. The branch of law regulating the right to resort to armed force is commonly referred to as jus ad bellum . Since 1945, it is incorporated in the Charter of the United Nations and its collective security mechanism. But this concept of self-defense only allows measures that are “proportional” to the armed attack and necessary to respond to it.
International humanitarian law applicable to armed conflicts ( jus in bello ) uses the principle of proportionality to limit the damages caused by military operations on civilian population and objects. Once a State has resorted to the use of armed force, jus in bello kicks in to regulate and restrain the use of force in times of armed conflict.
IHL provides that parties to the conflict must distinguish between civilian objects and military objectives, notably by using specific methods of warfare. Nonetheless, the attack of a legitimate target can cause damage on civilian persons and objects protected by IHL. The principle of proportionality complements other IHL principles such as the one of distinction to evaluate the legality of military activities. IHL prohibits attacks that may cause “incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated” (API Arts. 51, 57). The principle of proportionality therefore encompasses different elements in jus ad bellum and jus in bello . In the second case, it goes beyond the proportionality requirement between a military attack and the response to it. It obliges to balance the military advantages sought and the damage and civilian losses related to it. The proportionality requirement also applies to reprisals after an attack. The principle of proportionality is now recognized as a rule of customary law, applicable in both international and non-international armed conflicts (Rule 14 of the 2005 ICRC customary IHL study).
Proportionality is one of the key principles that enables and fosters a concrete debate on the limitations of military action and on the space that must be left for humanitarian operations within situations of conflict. This notion allows certain forms of suffering to be qualified as unnecessary. It does not mean that causing other kinds of harm is acceptable; rather, it reflects the fact that humanitarian law forbids suffering that is caused in no direct relation to a concrete military advantage and in disproportion with it.
The proportional nature of a reprisal in relation to the initial attack is the element that makes the distinction between a reprisal that is acceptable under the law of armed conflict and an act of revenge, which is always prohibited. Humanitarian law clearly establishes the responsibility of military commanders with regard to the respect for this principle.
The Statute of the International Criminal Court (ICC), adopted on 17 July 1998 and entered into force on 1 July 2002, also considers such acts as war crimes and includes them among the crimes over which it has jurisdiction. It adds to this definition the act of “intentionally launching an attack in the knowledge that such attack will cause incidental loss of life or injury to civilians or damage to civilian objects or widespread, long-term and severe damage to the natural environment which would be clearly excessive in relation to the concrete and direct overall military advantage anticipated” (Art. 8.2.b.iv of ICC Statute).
Decisions of international tribunals have specified the content of these obligations (infra Jurisprudence).
Proportionality of Restrictions to Human Rights in Situations of Internal Disturbances
The issue of the proportionality of restrictions to human rights imposed by a State in the name of national security or the defense of public order arises in many situations such as internal disturbances or the fight against terrorism, situations in which the intensity of violence does not trigger the application of humanitarian law. International conventions on human rights and national or regional courts are thus in charge of recalling the context and content of the requirement of proportionality in such situations.
From the jurisprudence, it appears that human rights remain applicable in these situations, subject to derogations made by States in accordance with the procedures provided for this purpose. Jurisprudence also states that in these circumstances, decisions made by the executive power remain subject to the control of national and international judges. The latter retain the final authority and responsibility to evaluate the adequacy and proportionality between the restriction of individual rights and the argument of “necessity” used by the government to justify its actions (infra Jurisprudence).
Proportionality of Sanctions
Proportionality is also used in reference to fundamental judicial guarantees, ensuring that the punishment is proportionate to the crime. This is reflected in the Geneva Conventions, which establish that “the courts [of the occupying power] shall apply . . . the principle that the penalty shall be proportioned to the offence” (GCIV Art. 67).
- International Court of Justice (ICJ)
ICJ recalled that “self-defense […] warrant[s] only measures which are proportional to the armed attack and necessary to respond to it, a rule well established in customary international law” ( Military and Paramilitary Activities in and against Nicaragua [ Nicaragua v. United States of America ], Merits, Judgment, ICJ Reports 1984, p. 14, para. 176).
In the ICJ judgment of 1996 on the legality of the use of nuclear weapons, Judge Higgins held that “the principle of proportionality, even if finding no specific mention, is reflected in many provisions of Additional Protocol I to the Geneva Conventions of 1949. Thus even a legitimate target may not be attacked if the collateral civilian casualties would be disproportionate to the specific military gain from the attack” ( Legality of the Threat or Use of Nuclear Weapons , Advisory Opinion, ICJ Reports 1996, p. 226, Separate Opinion of Judge Higgins, p. 587).
- International Criminal Tribunal for the Former Yugoslavia (ICTY)
According to the ICTY, the principle of proportionality means that incidental and involuntary damages caused to the civilian population during a military attack shall not be excessive in comparison to the direct military advantage obtained.
International law contains a general principle prescribing that reasonable care must be taken in attacking military objectives so that civilians are not needlessly injured through carelessness. Attacks, even when they are directed against legitimate military targets, are unlawful if conducted using indiscriminate means or methods of warfare, or in such a way as to cause indiscriminate damage to civilians ( Kupreskic Case , ICTY Trial Chamber, 14 January 2000, para. 524). In the Kupreskic Case , the Trial Chamber considered that it was beyond dispute that, at a minimum, large numbers of civilian casualties would have been interspersed among the combatants. It continued: “The point which needs to be emphasized is the sacrosanct character of the duty to protect civilians, which entails, amongst other things, the absolute character of the prohibition of reprisals against civilian populations.” Even if it could be proved that the population was not entirely civilian but comprised some armed elements, still no justification would exist for widespread and indiscriminate attacks against civilians. Indeed, even in a situation of full-scale armed conflict, certain fundamental norms still serve to unambiguously outlaw such conduct, such as rules pertaining to proportionality (para. 513). The judges declared that: “In the case of attacks on military objectives causing damage to civilians, international law contains a general principle prescribing that reasonable care must be taken in attacking military objectives so that civilians are not needlessly injured through carelessness” (para. 524). They further recalled that these principles have to some extent been spelled out in Articles 57 and 58 of the First Additional Protocol of 1977. Such provisions, it would seem, are now part of customary international law, not only because they specify and flesh out general pre-existing norms, but also because they do not appear to be contested by any State, including those that have not ratified the Protocol. Admittedly, even these two provisions leave a wide margin of discretion to belligerents by using language that might be regarded as leaving the last word to the attacking party. Nevertheless, this is an area where the “elementary considerations of humanity” should be fully used when interpreting and applying loose international rules, on the basis that they are illustrative of a general principle of international law (para. 524).
The ICTY admits that it may be easier to spell out a general principle of proportionality, rather than to apply it to a specific situation, because a balancing exercise must be done between different values and quantities. In the NATO bombing campaign against Serbia, the ICTY considered that the issue of whether the principle of proportionality was respected should be analyzed on a case-by-case basis, according to an objective criterion: the “responsible command” assessment. Therefore, the ICTY refuses to rely on an assessment made by a human rights organization. Rather, it considers that the questions that remain unresolved once one decides to apply the principle of proportionality include the following:
What are the relative values to be assigned to the military advantage gained and the injury to non-combatants and/or the damage to civilian objects?
What do you include or exclude in totaling these sums?
What is the standard of measurement in time or space?
To what extent is a military commander obligated to expose his own forces to danger in order to limit civilian casualties or damage to civilian objects? ( Final Report to the Prosecutor by the Committee Established to Review the NATO Bombing Campaign against the Federal Republic of Yugoslavia , ICTY, 13 June 2000, para. 49; available at http://www.un.org/icty/pressreal/nato061300.htm ).
- European Court of Human Rights (ECHR)
In its judgment in the case of Aksoy v. Turkey , the ECHR recalled that “it falls to each Contracting State, with its responsibility for ‘the life of [its] nation,’ to determine whether that life is threatened by a ‘public emergency’ and, if so, how far it is necessary to go in attempting to overcome the emergency. . . . Nonetheless, Contracting Parties do not enjoy an unlimited discretion. It is for the Court to rule whether, inter alia, the States have gone beyond the ‘extent strictly required by the exigencies’ of the crisis.” Consequently, the derogative measures must be strictly required by the exigencies of the situation ( Aksoy v. Turkey , Application no. 21987/93, Judgment [Chamber], 18 December 1996, para. 68).
- Inter-American Court for Human Rights
In its judgment of 1988, the Inter-American Court for Human Rights affirmed that “regardless of the seriousness of certain actions and the culpability of the perpetrators of certain crimes, the power of the State is not unlimited, nor may the State resort to any means to attain its ends” ( Velasquez Rodriguez v. Honduras , I/A Court H.R. [Ser. C.], no. 4, 1, 1988, para. 154).
- Israel Supreme Court
In a judgment of 1999 concerning the examination of the legality of using exceptional methods of interrogation in the context of the fight against terrorism, the Israel Supreme Court affirmed that neither international law nor national law recognized the argument of “necessity defence” to resort to torture or physical means during interrogations in the context of the fight against terrorism. The Court was of the opinion that this argument cannot authorize the use of physical means to allow investigators to execute their duties in circumstances of necessity. The Court affirmed that general directives governing the use of physical means during interrogations must be rooted in an authorization prescribed by law and not in defenses to criminal liability. The “necessity” defense cannot constitute an “ex-ante” basis for rules regarding an interrogation ( Public Committee against Torture in Israel v. the Government of Israel , HCJ 5100/94, 26 May 1999, paras. 36–37).
In a judgment of 2004 concerning the examination of the legality of the intervention of the Israel armed forces in Rafah (Gaza Strip), the Israel Supreme Court recognized that the argument of “necessity” can justify a military operation, but recalled that such a military operation can be legitimate from a military point of view but still be unlawful. The Court affirmed that judges have to examine the legality of military operations through the lens of the proportionality principle.
Judicial review does not examine the wisdom of the decision to carry out military operations. The issue addressed by judicial review is the legality of the military operations. Therefore we presume that the military operations carried out in Rafah are necessary from a military viewpoint. The question before us is whether these military operations satisfy the national and international criteria that determine the legality of these operations. The fact that operations are necessary from a military viewpoint does not mean that they are lawful from a legal viewpoint. Indeed, we do not replace the discretion of the military commander in so far as military considerations are concerned. That is his expertise. We examine their consequences from the viewpoint of humanitarian law. That is our expertise. ( Physicians for Human Rights v. the Commander of IDF Forces in the West Bank , HCJ 2117/02, 30 May 2004, para. 9)
In a judgment of 2005 relative to the examination of the Israel policy of targeted killings in the context of the fight against terrorism after the Second Intifada, the Israel Supreme Court confirmed its 1999 jurisprudence on the judicial control of the proportionality of derogations. It affirmed that it is necessary to find a balance between imperative national security and individual rights: “not every sufficient means is also legal. The ends do not justify the means. . . . That balancing casts a heavy load upon the judges, who must determine—according to the existing law—what is permitted, and what is forbidden” ( Public Committee against Torture in Israel v. the Government of Israel , HCJ 769/02, 11 December 2005, para. 63). The Court recognized that the principle of proportionality is a general principle of international law, and one of the core principles of humanitarian law in general, especially in situations of military occupation (paras. 41, 42). The Court held that
the principle of proportionality arises when the military operation is directed toward combatants and military objectives, or against civilians at such time as they are taking a direct part in hostilities, yet civilians are also harmed. The rule is that the harm to innocent civilians caused by collateral damage during combat operations must be proportional. . . . Civilians might be harmed due to their presence inside of a military target, such as civilians working in an army base; civilians might be harmed when they live or work in, or pass by, military targets; at times, due to a mistake, civilians are harmed even if they are far from military targets; at times civilians are forced to serve as “human shields” from attack upon a military target, and they are harmed as a result. In all those situations, and in other similar ones, the rule is that the harm to the innocent civilians must fulfill, inter alia, the requirements of the principle of proportionality. (para. 42)
The principle of proportionality applies in every case in which civilians are harmed at such time as they are not taking a direct part in hostilities. A manifestation of this customary principle can be found in The First Protocol, pursuant to which indiscriminate attacks are forbidden § 51(4). (para. 43)
The proportionality test determines that attack upon innocent civilians is not permitted if the collateral damage caused to them is not proportional to the military advantage (in protecting combatants and civilians). In other words, attack is proportional if the benefit stemming from the attainment of the proper military objective is proportional to the damage caused to innocent civilians harmed by it. That is a values based test. It is based upon a balancing between conflicting values and interests. . . . It is accepted in the national law of various countries. It constitutes a central normative test for examining the activity of the government in general, and of the military specifically, in Israel. (para. 45)
That aspect of proportionality is not required regarding harm to a combatant, or to a civilian taking a direct part in the hostilities at such time as the harm is caused. Indeed, a civilian taking part in hostilities is endangering his life, and he might—like a combatant—be the objective of a fatal attack. That killing is permitted. However, that proportionality is required in any case in which an innocent civilian is harmed. Thus, the requirements of proportionality stricto senso must be fulfilled in a case in which the harm to the terrorist carries with it collateral damage caused to nearby innocent civilians. . . . Performing that balance is difficult. Here as well, one must proceed case by case, while narrowing the area of disagreement. Take the usual case of a combatant, or of a terrorist sniper shooting at soldiers or civilians from his porch. Shooting at him is proportional even if as a result, an innocent civilian neighbour or passer-by is harmed. That is not the case if the building is bombed from the air and scores of its residents and passers-by are harmed. . . . The hard cases are those which are in the space between the extreme examples. There, a meticulous examination of every case is required; it is required that the military advantage be direct and anticipated (see §57(2)(iii) of The First Protocol). Indeed, in international law, as in internal law, the ends do not justify the means. The state’s power is not unlimited. Not all of the means are permitted. . . . However, when hostilities occur, losses are caused. The state’s duty to protect the lives of its soldiers and civilians must be balanced against its duty to protect the lives of innocent civilians harmed during attacks on terrorists. That balancing is difficult when it regards human life. It raises moral and ethical problems. . . . Despite the difficulty of that balancing, there’s no choice but to perform it. (para. 46)
The approach is similar regarding proportionality. The decision of the question whether the benefit stemming from the preventative strike is proportional to the collateral damage caused to innocent civilians harmed by it is a legal question, the expertise about which is in the hands of the judicial branch. . . . Proportionality is not a standard of precision. At times there are a number of ways to fulfill its conditions. A zone of proportionality is created. It is the borders of that zone that the Court guards. The decision within the borders is the executive branch’s decision. That is its margin of appreciation. (para.58)
For Additional Information: Amnesty International. “Collateral Damage” or Unlawful Killings? Violations of the Laws of War by NATO during Operation Allied Force . Available at http://www.amnesty.org/ailib/intcam/kosovo .
Cannizzaro, Enzo. “Contextualizing Proportionality: Jus ad Bellum and Jus in Bello in the Lebanese War.” International Review of the Red Cross 864 (December 2006): 779–92.
Dinstein, Yoram. “Collateral Damage and the Principle of Proportionality.” In New Wars, New Laws? , edited by David Wippman and Matthew Evangelista, 211–24. New York: Transnational, 2005.
Henckaerts, Jean-Marie, and Louise Doswald-Beck, ed. Customary International Law . Vol. 1, The Rules . Cambridge: Cambridge University Press, 2005, part 1, chap. 4.
ICTY. Final Report to the Prosecutor by the Committee Established to Review the NATO Bombing Campaign against the Federal Republic of Yugoslavia. Available at http://www.un.org/icty/pressreal/ato061300.htm .
Jaworski, Eric. “Military Necessity and Civilian Immunity: Where Is the Balance?” In International Crime and Punishment, Selected Issues , edited by Sienho Yee, 2:87–127. Lanham, MD: University Press of America, 2004.
John-Hopkins, Michael. “Regulating the Conduct of Urban Warfare: Lessons from Contemporary Asymmetric Armed Conflicts.” International Review of the Red Cross 878 (June 2010): 469–93.
Mulinen, Frederic de. Handbook on the Law of War for Armed Forced . Geneva: ICRC, 1989.