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Proportionality under International Humanitarian Law: The "Reasonable Military Commander"

Updated: May 12, 2020

Authors: Ian Henderson & Kate Reece


The principle of proportionality protects civilians and civilian objects against expected incidental harm from an attack that is excessive to the military advantage anticipated from the attack. However, despite its status as a fundamental norm of international humanitarian law (IHL), key terms are not defined in relevant treaties nor do they benefit from critical judicial explanation. This has caused challenges for both academics and military commanders alike in explaining and applying the test for proportionality.

The Article expands upon two points that were raised and generated interesting discussion at The Second Israel Defense Forces International Conference on the Law of Armed Conflict during a panel that dealt with contemporary issues in proportionality. Those two issues are:

  1. What does the “reasonable military commander” standard for assessing proportionality entail?

  2. Should “reverberating effects” (i.e., collateral effects that are only expected to materialize in the long term) be accounted for as part of the assessment of collateral damage?


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