In Honor of Françoise Hampson – Parsing Proportionality

Editors’ note: This post is part of a series to honor Françoise Hampson, who passed away on April 18, 2025. These posts recognize Professor Hampson’s work and the significant contribution her scholarship made to our understanding of international law.

It is a professional honor and personal pleasure to offer this essay in honor of my very dear friend Françoise Hampson, whom I miss very much. Her achievements in the academy require no embellishment; they are well known to all who work with the law of armed conflict, international human rights law, and related fields. But what truly distinguished Françoise was her generosity to her students, to her colleagues, and even to strangers she met for the first time. In many ways, kindness is the most lasting measure of a life well-lived, and by that measure, her impact was immeasurable.

In terms of scholarship, what made Françoise stand out was an almost unparalleled ability to move with precision and fluency across distinct legal regimes. A true legal polyglot, she was as comfortable teaching the law of armed conflict to military officers as she was litigating in a human rights tribunal or discussing State responsibility at an academic conference. That ease stemmed from a deep understanding that international law is a web of overlapping regimes, each with its own logic, history, and vocabulary. She appreciated that similar terms appear across different regimes, and that those terms must be interpreted carefully within their doctrinal contexts. Few concepts illustrate this reality more clearly than proportionality.

In that spirit, I offer this wave-top survey of proportionality to explain how proportionality operates differently in the jus ad bellum, the law of armed conflict (LOAC), international criminal law (ICL), international human rights law (IHRL), and the law of State responsibility. My aim is practical, to assist legal advisers, in and out of uniform, to distinguish among the various uses of the term, thereby avoiding the frequent missteps that arise when the concept of proportionality applicable in one regime migrates into another. As someone who cherished her relationships with practitioners and felt that they were the real guardians of the law, I think Françoise would have liked that.

Self-Defense Proportionality 

The jus ad bellum governs the resort to force by States. Article 2(4) of the UN Charter, which reflects customary international law, is the fulcrum upon which it rests. It states, “All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any State, or in any other manner inconsistent with the Purposes of the United Nations.”

There are two exceptions to the prohibition found within the four corners of the Charter. The first is a Security Council authorization or mandate to use force under Chapter VII. The other is self-defense. A customary rule, it finds expression, in relevant part, in Article 51 of the Charter as follows, “Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security.”

There are significant unsettled issues surrounding the application of the right of self-defense, including the precise threshold at which a hostile act constitutes an “armed attack,” the question of when the right of self-defense matures in advance of the armed attack, and the contentious matter of whether large-scale attacks by non-State actors can trigger the right. Nonetheless, there is universal agreement that every exercise of self-defense must satisfy two requirements: necessity; and proportionality (Paramilitary Activities, para. 176; Nuclear Weapons, para. 41; Oil Platforms, paras. 43, 76).

Necessity refers to the need to use forcible measures to address an armed attack. It asks whether the armed attack can be stopped or repelled by measures short of force. Proportionality, by contrast, is about the nature and extent of the forcible response. Unfortunately, it has been the subject of frequent misinterpretation. For instance, it is sometimes styled as requiring a degree of equivalency between the force used in the armed attack and the victim State’s forcible response. As will be seen, this is a requirement for proportionality in other regimes, but not for self-defense. Moreover, self-defense proportionality is often characterized as limiting the amount of civilian harm that may be caused in a defensive response. But collateral damage is an aspect of the LOAC proportionality rule; it has no direct bearing on compliance with the proportionality rule in the jus ad bellum.

Correctly understood, self-defense proportionality limits the type and amount of force used to that required to prevent an imminent armed attack or repel an ongoing one. Professor Yoram Dinstein has described it as a “standard of reasonableness,” while Professor David Kretzmer labels it a “means-end” test. As these characterizations illustrate, whether a response is “proportionate” is context dependent. The proportionality assessment must account for all relevant circumstances, including the operational environment, the capabilities of the attacker, and the feasible defensive options available. And with respect to those options, that which is the least forcible in the sense of harm caused must be chosen, although I caution that the condition of feasibility necessarily leaves States a wide margin of appreciation. Importantly, it is appropriate to consider the threat to one’s own forces when assessing feasibility.

Such determinations are not framed by an “in-kind” requirement. For instance, a State facing an armed attack by cyber means need not restrict its response to cyber operations if a kinetic strike is more effective and less harmful. Indeed, if such a response can effectively neutralize the armed attack and be less destructive than a kinetic attack, that option must be taken. Nor must the response be limited to the specific units or infrastructure used to mount the attack. It may be entirely permissible to strike other military assets the attacking State values in order to compel the attacker to terminate its operations, although the operations must still comply with the overarching principle of proportionality (Oil Platforms, para. 77). Of course, such operations must also comply with the law of armed conflict, thereby limiting targets to those qualifying as military objectives.

The exercise of self-defense must accordingly be shaped to the context in which it is being applied. But it must also comply with certain restrictions on the ways that exercise is carried out. These are found principally in LOAC and, to a lesser extent, IHRL.

Law of Armed Conflict Proportionality

A practical challenge decision-makers, operators, and observers frequently encounter is the tendency to collapse jus ad bellum and LOAC proportionality into a single inquiry. This is particularly common in high-tempo environments. However, it is essential to distinguish between proportionality as it operates in the jus ad bellum and its LOAC counterpart; they are distinct, although they often apply in parallel. In LOAC, which applies only during international or non-international armed conflict, proportionality appears in several differing guises.

Attack

As noted, self-defense proportionality does not consider collateral damage except as it relates to harm caused as between the options available to a State when defending itself against an armed attack. By contrast, harm to civilians and civilian objects is precisely the issue in the rule of proportionality applicable during “attacks,” a LOAC term of art (Additional Protocol I, art. 49).

In provisions that reflect customary law, Additional Protocol I of the Geneva Conventions sets forth the rule of proportionality applicable during the so-called “conduct of hostilities” (International Committee of the Red Cross (ICRC), Customary IHL, rule 14). Article 51(5)(b) prohibits as indiscriminate “an attack which may be expected to 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.” Similarly, Article 57, which mandates taking “active precautions in attack,” requires “those who plan or decide upon an attack” to “refrain from deciding to launch” such attacks, and requires their cancellation or suspension “if it becomes apparent” that the attack would violate the prohibition.

Several features of the proportionality rule warrant attention. First, it applies only to civilian deaths, injuries, and damage to civilian objects. There may be some play in the notion of damage, as reflected in a growing trend to treat the loss of cyber infrastructure functionality as damage under the conduct of hostilities rules (Tallinn Manual 2.0, rule 92 commentary). Still, other consequences, such as inconvenience or fear falling short of terror, are not factored into the analysis.

Second, the assessment is ex ante, not post factum. What matters are the expectations of those who planned, approved, and executed an attack at the time they did so. Proportionality is not assessed by looking in hindsight at an attack’s consequences, except to the extent those consequences evidence what those individuals believed or should have believed.

State practice confirms this ex ante approach, and it appears in numerous military manuals. The U.S. Department of Defense (DoD) Law of War Manual, for example, provides that “an assessment of whether a decision-maker has complied with the legal requirements must be based on the information available to that person at the time” (§ 5.10.2.3). Similarly, the Canadian Law of Armed Conflict Manual observes, “Consideration must be paid to the honest judgement of responsible commanders, based on the information reasonably available to them at the relevant time, taking fully into account the urgent and difficult circumstances under which such judgements are usually made” (§ 418).

Third, the rule is often mischaracterized as a balancing test. Yet, it is not a mathematical calculation that would, for instance, preclude an attack that kills six combatants and seven civilians. Rather, each attack must be assessed on its merits. To illustrate, killing the commander of a major enemy unit could seriously disrupt that unit’s ability to fight effectively. This would be a substantial military advantage justifying significant collateral damage. But killing a few enemy soldiers remote from the front lines might yield so little military advantage that it would justify no civilian deaths.

The correct proportionality standard is “excessiveness.” Only excessive collateral damage renders an attack disproportionate, and therefore unlawful. As noted in the Harvard Air and Missile Warfare Manual, an attack is excessive “when there is a significant imbalance between the military advantage anticipated, on the one hand, and the expected collateral damage to civilians and civilian objects, on the other” (p. 98). In this regard, it is essential to point out that “extensive” collateral damage is not necessarily excessive; this is so despite an incorrect suggestion to the contrary in an ICRC commentary to Additional Protocol I (para. 1980).

Finally, there has recently been some confusion over which military advantage and which collateral damage are to be factored in when applying the rule. It is well accepted as a matter of customary law that “the military advantage anticipated from an attack is intended to refer to the advantage anticipated from the attack considered as a whole and not from isolated or particular parts of that attack” (see e.g., UK Statement Upon Ratification). For instance, consider a ruse of warfare designed to trick the enemy into believing a major attack into a particular area is imminent by striking air defense assets there. In response, the enemy diverts assets into the area, but the attack will actually occur elsewhere. The military advantage of the strikes lies in causing the enemy to misorient its forces, not in destroying the air defenses.

And only collateral damage from a particular attack, which may consist of multiple strikes, factors into the proportionality calculation. In the present state of the law, there is no basis for aggregating collateral damage across multiple attacks or an entire campaign and comparing that aggregate to the overall strategic military advantage of the operation.

Reprisal

In LOAC, a reprisal is a response to the enemy’s unlawful act that would itself be unlawful but for the fact that it qualifies as a reprisal (see my discussion of reprisals here). Treaty law severely limits many forms of reprisal (see Geneva Convention (GC) I, art. 46; GC II, art. 47; GC III, art.13; GC IV, art. 33, AP I, arts. 20, 51(6), 52(1), 53(c), 54(4), 55(2), 56(4); Cultural Property Convention, art. 4(4); Convention on Conventional Weapons, Amended Protocol II, art. 3(7)). While the customary status of the reprisal prohibitions in the 1949 Geneva Conventions is universally acknowledged, whether other treaty-based prohibitions, except those mirroring the Geneva Conventions, reflect customary law is less settled (ICRC, Customary IHL, rules 146-147).

Because reprisals are otherwise unlawful, strict conditions are imposed upon them. Five are generally recognized (ICRC, Customary IHL, rule 145; DoD, Law of War Manual, §18.18.2; Kupreškić, para. 535). Most importantly, a reprisal’s sole permissible purpose is to compel the enemy to comply with LOAC; a reprisal may not be primarily motivated by a desire for revenge or retaliation. This leads to the second condition, that the reprisal action be terminated as soon as the enemy complies with its legal obligations. Additionally, reprisals are not permissible if other means of compelling compliance are available, and the decision to engage in a reprisal must be taken at a high level.

The last condition is that a reprisal must be proportionate to the original wrong; it must have a reasonable relationship to the gravity and nature of the enemy’s unlawful conduct (Naulilaa arbitration, p. 1028; Nuclear Weapons, para. 46). Although complying with the proportionality requirement does not require reprisals to be in-kind, the DoD Law of War Manual sensibly observes that “[i]dentical reprisals are the easiest to justify as proportionate, because subjective comparisons are not involved” (§ 18.18.2.4).

This begs the question of how to make the subjective comparison in cases where the reprisal involves a LOAC rule other than the one that the enemy is violating. In such cases, a rule of reason applies. For instance, the DoD Law of War Manual cautions that a reprisal should not be “unreasonable or excessive compared to the adversary’s violation” (§ 18.18.2.4), and the International Criminal Tribunal for the former Yugoslavia (ICTY) has explained “that the reprisals must not be excessive compared to the precedent unlawful act of warfare” (Kupreškić, para. 535). Thus, a reprisal must be proportionate to the gravity of the LOAC violation to which it responds, both qualitatively and quantitatively.

Occupation Law

Proportionality plays a significant legal role during belligerent occupation. The touchstone of occupation law is Article 43 of the 1907 Hague Regulations, which reflects customary law binding on all States. Setting a baseline for an occupant’s authority and obligations, it provides, “The authority of the legitimate power having in fact passed into the hands of the occupant, the latter shall take all the measures in his power to restore, and ensure, as far as possible, public order and safety, while respecting, unless absolutely prevented, the laws in force in the country.” Thus, the occupying power must balance restoring public order against a presumption of respect for existing law in the occupied territory. Deviations from the latter must be “absolutely necessary,” which can be understood as ensuring that measures that do deviate are not excessive and tailored to genuine necessity.

Although Article 43 is the foundation of occupation law, the 1949 Fourth Geneva Convention provides detailed guidance on its content. Today, these rules, like Article 43, are considered reflective of customary law. Some of them encompass a proportionality requirement.

Article 53, for instance, provides that “Any destruction by the Occupying Power of real or personal property belonging individually or collectively to private persons, or to the State, or to other public authorities, or to social or cooperative organizations, is prohibited, except where such destruction is rendered absolutely necessary by military operations.” Again, the “absolutely necessity” effectively reflects a proportionality standard that permits only the minimum destruction needed in the circumstances to achieve a legitimate military objective.

Or consider the Article 67 requirement that “The [properly constituted non-political military] courts shall apply only those provisions of law which were applicable prior to the offence, and which are in accordance with general principles of law, in particular the principle that the penalty shall be proportioned to the offence.” A new 2025 ICRC Commentary to the Fourth Geneva Convention explains, “This principle was highlighted because of certain abuses committed during the Second World War, when heavy punishments, including the death penalty, were inflicted for minor offences such as listening to enemy radio programmes or going on strike” (para. 3831).

International tribunals have emphasized the role proportionality can play during occupation. In its Wall advisory opinion, for example, the International Court of Justice observed that the Court,

from the material available to it, is not convinced that the specific course Israel has chosen for the wall was necessary to attain its security objectives. The wall, along the route chosen, and its associated regime gravely infringe a number of rights of Palestinians residing in the territory occupied by Israel, and the infringements resulting from that route cannot be justified by military exigencies or by the requirements of national security or public order (para. 137).

It concluded that as built, the wall violated both LOAC and IHRL. Although using the term “necessary,” it was essentially finding that Israel’s action in building the wall was disproportionate in the sense of going too far.

Israel’s Supreme Court has provided what is perhaps the most granular explanation of proportionality during occupation in its Mara’abe judgment.

The principle of proportionality is based on three subtests which fill it with concrete content. The first subtest calls for a fit between goal and means. There must be a rational link between the means employed and the goal one is wishing to accomplish. The second subtest determines that of the gamut of means which can be employed to accomplish the goal, one must employ the least harmful means. The third subtest demands that the damage caused to the individual by the means employed must be of appropriate proportion to the benefit stemming from it. Note that “at times there is more than one way to satisfy the proportionality demand. In such situations, a zone of proportionality (similar to the zone of reasonableness) should be recognized. Any means which the administrative body chooses from within the zone is proportional” (para. 30, quoting The Beit Sourik Case, p. 840).

International Criminal Law

Violations of LOAC entail the responsibility of States, not the individuals who engage in the prohibited conduct. By contrast, international criminal law deals with individual responsibility for the commission of international offenses such as war crimes and crimes against humanity.

In Article 8(2)(b)(iv), the Rome Statute of the International Criminal Court expressly treats a violation of the proportionality rule as a war crime during international armed conflict. It states,

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.

As a general matter, the same issues cited above regarding the LOAC rule of proportionality apply here. However, there are two significant differences.

To begin, it is not enough for a prosecutor to show that a reasonable commander should have known about the excessive harm; the attacker must have subjectively known the harm would occur and launched the attack. According to Article 30(3) of the Rome Statute, “A person has knowledge of a circumstance or a consequence when that person is aware that it exists or will occur in the ordinary course of events.”

The other difference is that Article 8 imposes a higher “clearly excessive” standard for the resulting harm to civilians and civilian objects. In other words, the disproportionality must be egregious. The result of the two is a much higher evidentiary burden when establishing individual criminal responsibility for disproportionate attacks than in cases of State responsibility.

Although there is no standalone proportionality offense in the statutes of other international criminal tribunals, they have dealt with the issue. For instance, in Galić, the ICTY considered proportionality in the context of indiscriminate attacks when assessing whether the accused had committed the war crime of “violating the laws or customs of war” during a sniping and shelling campaign into Sarajevo (ICTY Statute, art. 3).

Notably, the tribunal distinguished LOAC proportionality from its ICL counterpart. Referring to the former, it explained that “in determining whether an attack was proportionate it is necessary to examine whether a reasonably well-informed person in the circumstances of the actual perpetrator, making reasonable use of the information available to him or her, could have expected excessive civilian casualties to result from the attack.” But for criminal responsibility, “the Prosecution must prove, instead of the [LOAC] mens rea requirement, that the attack was launched wilfully and in knowledge of circumstances giving rise to the expectation of excessive civilian casualties” (Galić, paras. 58-59).

The Rome Statute also includes a provision similar to Article 67 of the Fourth Geneva Convention, which was discussed above in the context of occupation law proportionality. According to Article 81(2)(a), “A sentence may be appealed, in accordance with the Rules of Procedure and Evidence, by the Prosecutor or the convicted person on the ground of disproportion between the crime and the sentence.” This reinforces the fundamental requirement that criminal penalties reflect the gravity and individual circumstances of the offense. As is apparent, the ICL and LOAC counterparts have essentially the same effect.

Human Rights Proportionality 

International human rights law contemplates limitations by States on the exercise and enjoyment of human rights obligations other than those that are “absolute” in character, such as the prohibition on torture, slavery, and the right to hold an opinion. For instance, Article 6 of the International Covenant for Civil and Political Rights states, “No one shall be arbitrarily deprived of his life.” The reference to “arbitrary” implies that there are situations that justify the State taking action that limits the enjoyment of the right to life.

Similarly, Article 10(2) of the European Convention on Human Rights provides that the exercise of freedom of expression,

may be subject to such formalities, conditions, restrictions or penalties as are prescribed by law and are necessary in a democratic society, in the interests of national security, territorial integrity or public safety, for the prevention of disorder or crime, for the protection of health or morals, for the protection of the reputation or rights of others, for preventing the disclosure of information received in confidence, or for maintaining the authority and impartiality of the judiciary.

Again, the rights of individuals are balanced against the needs of society.

Such limitations are conditioned on four requirements. First, domestic law must prescribe them, and that law must be accessible to individuals who may be affected. Second, limitations must have a legitimate aim, such as public health, public order, or national security. Third, they must be necessary in the sense of being suitable for achieving the aim, and less intrusive measures must be unavailable or have been exhausted in attempts to do so.

The fourth requirement is that the limitation “be proportionate to the interest to be protected” (see, e.g., General Comment No. 27, para. 14). Whereas necessity asks whether a particular measure is essential to achieve a legitimate aim, proportionality concerns the balance between the limitation and that aim. A limitation is proportionate, therefore, when the benefits of achieving the legitimate aim outweigh the infringement on the individual right. That balance must exist with regard to both the law that provides for the limitation and its application. The requirement has been repeatedly confirmed by human rights courts (see, e.g., Sunday Times, para. 62; Handyside, para. 49; Öneryıldız, para. 107).

Importantly, limitations on the exercise or enjoyment of human rights “may not put in jeopardy the right itself” (General Comment No. 34, para. 21). The Human Rights Committee has explained that “the relation between right and restriction and between norm exception must not be reversed,” which means that the requirement of proportionality precludes limitations from being an exception that swallows the rule.

For instance, while it might be proportionate to arrest or detain criminals consistent with the requirements of due process, it is neither necessary nor proportionate to use deadly force against them in situations where there is no direct threat of death or grievous bodily injury to the law enforcement officials or others. Indeed, in the landmark McCann case, the European Court of Human Rights pointed out that,

in a democratic society, the Court must, in making its assessment, subject deprivations of life to the most careful scrutiny, particularly where deliberate lethal force is used, taking into consideration not only the actions of the agents of the State who actually administer the force but also all the surrounding circumstances including such matters as the planning and control of the actions under examination (para. 150).

State Responsibility Proportionality

Countermeasures

The law of State responsibility allows States to take “countermeasures” in response to a breach of an international law obligation that another State owes to it. A countermeasure is an action that would be an “internationally wrongful act” (unlawful) but for the fact that it is designed to compel another State (the “responsible State”) to desist in its unlawful conduct or to secure any reparations that might be due to the “injured State” because of that conduct. The International Law Commission has restated the customary rules regarding countermeasures in its Articles on State Responsibility (ASR) (arts. 22, 49-54).

Article 51 ASR restates the proportionality requirement for countermeasures. “Countermeasures must be commensurate with the injury suffered, taking into account the gravity of the internationally wrongful act and the rights in question” (see also Gabčíkovo-Nagymaros, para. 85). With countermeasures, therefore, proportionality approximates the common understanding of the term. It considers the harm caused by the responsible State’s internationally wrongful act and whether the harm the injured State’s countermeasure causes is out of balance with it.

In addition to actual harm, countermeasures proportionality also factors in the significance of the injured State’s legal right that has been affected and the importance of the responsible State’s legal right that will be affected by the countermeasure; thus, countermeasure proportionality includes a balancing of interests. The 1978 Air Services Agreement arbitration is commonly cited to illustrate this point. It concerned whether the United States and its Pan Am airline had a right under the 1946 Air Services Agreement to operate flights from the U.S. west coast to Paris with a change of gauge (size of aircraft) in London, and whether the retaliatory suspension of French flights to Los Angeles by the United States was lawful.​

In its award, the arbitral tribunal emphasized that “it is essential, in a dispute between States, to take into account not only the injuries suffered by the companies concerned but also the importance of the questions of principle arising from the alleged breach.” It concluded, “If the importance of the issue is viewed within the framework of the general air transport policy adopted by the United States Government and implemented by the conclusion of a large number of international agreements with countries other than France, the measures taken by the United States do not appear to be clearly disproportionate when compared to those taken by France” (para. 83). In other words, proportionality was assessed with reference to the purpose and functioning of the entire air services regime, not just the financial impact.

There is no requirement that, to be proportionate, the injured States direct its countermeasure at the responsible State’s entity that engaged in the unlawful conduct. Thus, for instance, if the responsible State’s navy repeatedly conducts operations in the injured State’s territorial sea in violation of the innocent passage regime (UN Convention on the Law of the Sea, arts. 17-19), proportionate countermeasures directed at ministry of interior assets would be permissible. Nor, as this example illustrates, does the proportionality requirement require the injured State’s countermeasure to breach the same obligation that the responsible State breached. In fact, there is no requirement that the same mechanism be used to conduct the countermeasure as was used in the responsible State’s internationally wrongful act. Thus, for example, an internationally wrongful act committed by cyber means need not be responded to with a cyber operation.

Because countermeasures are actions that would otherwise violate international law, they are subject to strict limitations and requirements. For instance, countermeasures involving the use of force are prohibited (ASR, art. 50(1)(a)). Nor may countermeasures include actions that affect fundamental human rights or that amount to an unlawful belligerent reprisal under the law of armed conflict (ASR, art. 50(1)(b & c)).

Reparations

Under the law of State responsibility, a State that has engaged in an internationally wrongful act must make “full reparation for the injury caused” (ASR, art. 31). The injury obviously includes material damage but can also extend to moral harm. Reparations can take the form of restitution (re-establishing the situation that existed before the wrongful act), compensation, or satisfaction (an acknowledgement of wrongfulness and an apology) (ASR, art. 34). The Permanent Court of International Justice recognized that the obligation to make reparations is customary in character in its 1928 Chorzów Factory judgment. The Court observed,

It is a principle of international law, and even a general conception of the law, that any breach of an engagement involves an obligation to make reparation … Reparation is the indispensable complement of a failure to apply a convention, and there is no necessity for this to be stated in the convention itself (p. 29).

The reparations due must be proportionate in the sense of making the injured State whole, to the extent possible. For instance, Article 35 of the ASR provides that restitution must not “involve a burden out of all proportion to the benefit deriving from restitution instead of compensation.” Similarly, Article 36 states that compensation must “compensate for the damage caused … insofar as such damage is not made good by restitution.” And Article 37 provides, “Satisfaction shall not be out of proportion to the injury and may not take a form humiliating to the responsible State.” The point is that the goal of reparations proportionality is to restore the injured State to the position it would have been in had the internationally wrongful act not occurred, not to punish the responsible State.

It is clear that the obligation to provide reparations extends to violations of LOAC. As noted in the DoD Law of War Manual, “A State that is responsible for an internationally wrongful act is under an obligation to make full reparation for the injury caused by that act. This principle also applies to the law of war in that a State that violates the law of war shall, if the case demands, be liable to pay compensation” (§ 18.16). The Second Protocol to the Cultural Property Convention expressly mentions the obligation (art. 38), while provisions in each of the four 1949 Geneva Conventions provide that States cannot absolve themselves of “liability incurred … in respect of [grave] breaches” (GC I, art. 51; GC II, art. 52; GC III, art. 131; GC IV, art. 148). Article 91 of Additional Protocol I is to the same effect. These rules are undoubtedly customary in character (ICRC, Customary IHL, rule 150; see also UNGA Resolution 60/147 (2005) on reparations to victims of LOAC violations).

Concluding Thoughts

Proportionality is one of the most widely used concepts in international law. However, its recurrence across different legal regimes should not lead to the mistaken assumption that it carries a single meaning. Rather, the nature, function, and analytical focus of proportionality vary substantially depending on whether one is dealing with the resort to force, the conduct of hostilities, the administration of occupied territory, the protection of human rights, the attribution of individual criminal responsibility, or assessing the responsibility of States for unlawful conduct. In each of these settings, proportionality reflects a bespoke balance between competing considerations: necessity and restraint; military necessity and humanitarian protection; State prerogatives and individual rights; and enforcement of the law and the prevention of excesses. Understanding these differences is essential to ensuring that the concept is applied faithfully and does not migrate inappropriately across normative boundaries.

That appreciation for nuance, and for the practical consequences of doctrinal clarity, is very much in the spirit of Françoise Hampson. She understood that precision in the use of terms like proportionality is essential to ensuring that the law operates as intended. Her ability to move elegantly across the various regimes discussed here reflected not only her scholarly wherewithal but also her commitment to ensuring that the law remains a meaningful tool for those applying it in complex and often fraught environments. If this essay succeeds in offering a clearer picture of proportionality’s many faces, it does so in tribute to Françoise’s example and her enduring contributions to the field.

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Michael N. Schmitt is Professor of Public International Law at the University of Reading (UK); Professor Emeritus a at the United States Naval War College; Visiting Research Professor at the International Institute of Humanitarian Law in San Remo, Italy; Affiliate at Harvard Law School’s Program in International Law and Armed Conflict; and General Editor of the Lieber Studies series (OUP).

The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense. 

Articles of War is a forum for professionals to share opinions and cultivate ideas. Articles of War does not screen articles to fit a particular editorial agenda, nor endorse or advocate material that is published. Authorship does not indicate affiliation with Articles of War, the Lieber Institute, or the United States Military Academy West Point.

 

 

 

 

 

 

 

Photo credit: U.S. Air Force, Melanie Casineau