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The Oxford Companion to International Criminal Justice edited by Cassese, Antonio (22nd January 2009)

Part B Issues, Institutions, and Personalities, P, Proportionality

Jean-Marie Henckaerts

From: The Oxford Companion to International Criminal Justice

Edited By: Antonio Cassese (Editor-in-Chief)


The principle of distinction and the prohibitions which flow from it against attacks against civilians and civilian objects (see civilians (attacks on)) do not cover civilian losses and damage which are the unintended result of an attack directed against a legitimate military objective. Such incidental civilian losses and damage are subject to the principle of proportionality (p. 470) which requires that they be proportionate to the military advantage anticipated from the attack. To this effect IHL prohibits attacks 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’ (Art. 51(5)(b) AP I). Such an attack is considered indiscriminate, i.e. of a nature to strike military objectives and civilians or civilian objects without distinction. All feasible precautions must be taken not to launch such attacks and to cancel or suspend those that are under way (Art. 57(2)(a)(iii) and (2)(b) AP I). These rules are additional to the obligation to take all feasible precautions in the choice of means and methods of attack with a view to avoiding, and in any event to minimizing, incidental civilian losses and damage (Art. 57(2)(a)(ii) AP I).

‘Launching an indiscriminate attack affecting the civilian population or civilian objects in the knowledge that such attack will cause excessive loss of life, injury to civilians or damage to civilian objects’ is a grave breach of AP I (Art. 85(3)(b)). Under t he ICCSt., ‘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 … which would be clearly excessive in relation to the concrete and direct overall military advantage anticipated’ is a war crime in international armed conflict (Art. 8(2)(b)(iv)). It should be noted that the words ‘clearly’ and ‘overall’ have been added to the ICCSt. definition compared to the definition in AP I.

Although the provisions in AP I on proportionality only apply to states parties thereto, they reflect customary international law today, including in non-international armed conflicts. The main problem with the principle of proportionality is not whether it exists, but what it means. A number of uncertainties continue to exist in this respect.

Firstly, the construction of the terms ‘concrete and direct military advantage’ is crucial. In practice, there seems to be a tendency to interpret the notion of military advantage in a very broad sense. The advantage must be military in nature, generally residing in gaining ground on or weakening or defeating enemy armed forces, but also, according to some states, in ensuring the security of the attacking forces. In addition, several states have asserted that the expression ‘military advantage’ refers to the advantage anticipated from the military attack considered as a whole and not only from isolated or particular parts of that attack. The relevant provision in the ICCSt. refers to the ‘concrete and direct overall military advantage anticipated’. The elements of crimes under the ICC include a footnote stating that: ‘The expression “concrete and direct overall military advantage” refers to a military advantage that is foreseeable by the perpetrator at the relevant time. Such advantage may or may not be temporally or geographically related to the object of attack.’ The second sentence covers attacks where the military advantage is planned to materialize at a later time and/or in a different place. An example is of the attacks by the Allies during World War II against targets in the Pas de Calais to deceive the Germans into believing that the Allied amphibious assault would occur there, rather than in Normandy. It is clear, however, that the term ‘overall’ military advantage cannot be read as a reference to the conflict as a whole. The expression ‘concrete and direct’ military advantage was used in order to indicate that the advantage must be ‘substantial and relatively close, and that advantages which are hardly perceptible and those which would only appear in the long term should be disregarded’ (Y. Sandoz, C. Swinarski and B. Zimmermann (eds), Commentary on the Additional Protocols (Geneva: ICRC, 1987), § 2209).

The requirement of foreseeability is therefore essential as it excludes reliance on ex post facto justifications. The evaluation of whether the incidental civilian losses and damage are likely to be excessive must be undertaken before the decision to launch the attack. Launching an attack on the blithe assumption that civilian losses and damage will not be excessive would not respect the law.

On the other hand, the question arises as to which civilian losses and damage are relevant: only those which are direct, or also those that are indirect (such as long-term disruption of civilian life due to destruction of water and electricity infrastructure)? If the concept of military advantage is interpreted widely, it seems logical to do the same for civilian losses and damage and to include these knock-on effects. It follows that the foreseeable military advantage of an operation must be weighed against the foreseeable civilian losses and damage, including the knock-on effects.

Thirdly, there is no mathematical formula as to how to weigh the civilian losses and damage against the military advantage anticipated. The assessment involves a subjective comparison of heterogeneous values in real-time, not based on hindsight. Commanders have to reach their decisions on the basis of their assessment of the information from all sources available to them at the relevant time. Their decision will depend on the context because the (p. 471) military advantage depends on the state of hostilities at the time. The Committee Established to Review the NATO Bombing Campaign Against the FRY suggested that the benchmark must be the ‘reasonable military commander’ (Final Report to the ICTY Prosecutor (2000), § 50).

To close the gaps of uncertainty left by the principle of proportionality, the ICTY has suggested that ‘in case of repeated attacks, all or most of them falling within the grey area between indisputable legality and unlawfulness, it might be warranted to conclude that the cumulative effect of such acts entails that they may not be in keeping with international law’ (Kupreškić and others (IT-95-16), TC, 14 January 2000, § 526).

jean-marie henckaerts

  • A. P.V. Rogers, ‘The Principle of Proportionality’, in H.M. Hensel (ed.), The Legitimate Use of Military Force: The Just War Tradition and the Customary Law of Armed Conflict (London: Ashgate, 2008), 189–218.