Proportionality in the conduct of hostilities : the incidental harm side of the assessment
London : Chatham House, December 2018
52 p. ; 30 cm
The rule of proportionality 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. This research paper analyses the key steps that belligerents must take to give effect to the rule, with a particular focus on one side of proportionality assessments – the expected incidental harm. Those undertaking proportionality assessments before or during an attack must consider whether the expected harm will be caused by the attack, and whether that harm could be expected (that is, was it reasonably foreseeable). For the purpose of proportionality assessments, injury to civilians includes disease, and there is no reason in principle to exclude mental harm, even though it is currently challenging to identify and quantify it. Damage to civilian objects includes damage to elements of the natural environment. Once the incidental harm to be considered has been identified, a value or weight must be assigned to it. This is then balanced against the value or weight of the military advantage anticipated from the attack to determine whether the harm would be excessive. In the determination of whether the expected incidental harm would be excessive compared to the anticipated military advantage, ‘excessive’ is a wide but not indeterminate standard.