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Some Reflections on the “Incidental Harm” Side of Proportionality Assessments

Updated: May 12, 2020

Author: Emanuela-Chiara Gillard


The prohibition of attacks expected to cause incidental loss of civilian life, injury to civilians, or damage to civilian objects that would be excessive in relation to the concrete and direct military advantage anticipated lies at the heart of the rules of international humanitarian law (IHL) regulating the conduct of hostilities. According to Article 51(5)(b) of the First Additional Protocol of 1977 to the Geneva Conventions of 1949 (AP I), a disproportionate attack is there now appears to be general agreement that it constitutes a rule of customary law applicable in international and non-international armed conflicts.2

The rule on proportionality represents the most apparent manifestation of the balance between military necessity and considerations of humanity that underpins IHL. As military operations are taking place in densely populated areas with increasing frequency, the rule’s significance for the protection of civilians has become even more key. It is of central relevance to the current discussions on the use of explosive weapons in populated areas.

Determining what falls into the two “sides” of the proportionality assessment as clearly as possible is essential to the proper application of the rule in practice. The expected “military advantage side” of the equation has received considerable attention; the “incidental harm side” less so—even though it is equally key in assessing the lawfulness of an attack. It raises a number of legal issues that need to be addressed by belligerents to ensure they are complying with the law. Proportionality is a challenging topic and is frequently misunderstood by nonexperts and the media, particularly while hostilities are unfolding. Addressing the incidental harm side of the assessment would also provide reassurance that this dimension is being given proper consideration.

This Article focuses on just some of the questions covered at the IDF panel, although there are many that warrant closer consideration.


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