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Four Comments on the Application of Proportionality under the Law of Armed Conflict

Updated: May 12, 2020

Author: Lieutenant Colonel Roni Katzir


The existence of the principle of proportionality as a norm is undisputed, and military commanders in armed conflicts around the world apply it continuously. As the principle is formulated in general terms—prohibiting attacks that may be expected to cause incidental loss of civilian life, injury to civilians, or damage to civilian objects, or a combination thereof, that would be excessive in relation to the military advantage anticipated—it is also clear that interpreting and applying the different elements of the principle is no simple task.

This Article shall consider four select issues regarding different elements of the principle of proportionality.

First is how to determine “excessive” (Part II). International law does not elaborate on how one must determine what is “excessive.” What is generally accepted, however, is that proportionality is assessed inter alia on the basis of subjective considerations and values. The Final Report to the Prosecutor Reviewing the NATO Bombing Campaign in the Federal Republic of Yugoslavia (FRY), for example, has espoused for this purpose the standard of a “reasonable military commander.” How should this standard be understood and applied?

Second is interpreting “military advantage” (Part III). Here, should the military context in which the attack or operation is taking place matter, and if so, to what extent?

Third is the impact of defensive systems on determining “military advantage” (Part IV). Many parties to conflicts have some sort of defensive measures to protect civilians from attack (from passive systems, such as shelters and air raid warnings systems, to active defensive systems, such as aerial defense facilities or rocket interception mechanisms). Should the apparent reduced lethality of enemy capabilities as a result of these systems be taken into account when assessing military advantage in attacks against the enemy?

Fourth is the impact of “force preservation” on determining “military advantage” (Part V). It is axiomatic that in conflict, preserving one’s forces is important. What role should this play in proportionality assessments?


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