The Disproportionate Confusion About Proportionality

Proportionality is a term commonly invoked to condemn infliction of civilian suffering during war. But just as pervasive is the misunderstanding of how it impacts both the authority to engage in hostilities, and the protection of civilians during hostilities.

What is proportionality?

Proportionality is a principle of law that has different meanings in different contexts. Its peacetime meaning is probably best understood in the context of self-defense.

In this context, it protects the aggressor by limiting the force used in response to the unlawful threat: only measures that are genuinely necessary to eliminate the threat are permissible.

Thus, when citizens or police use deadly force, we often ask whether that use was “excessive”, the opposite of proportional because it was more than was reasonably necessary.

Proportionality and self-defense

A similar concept applies to a state acting in self-defense. In this context, the state – whether responding to an unlawful armed attack by another state or an organized armed group like Hamas or ISIS (although there are some scholars who question whether non-state threat trigger the right of self defense) – is justified to use proportional force to terminate the threat, protect its population, and restore its security.

In military terms, proportionality in this context plays a critical role in the strategic scope and duration of a self-defense operation. Like an individual responding to an unlawful attack, the state is not restricted to a “tit for tat” response.

Instead, it must assess what military response is necessary to achieve the legitimate goal of self-defense. Like an individual responding to an actual or imminent unlawful attack, a military response that is credibly necessary and proportional to the nature of the overall threat distinguishes the lawful state self-defense from unlawful revenge or retribution.

Proportionality once conflict begins

Once hostilities are commenced, however, a different concept of proportionality comes into play, one derived from the international law of armed conflict (LOAC), or law of war.

This is where the misunderstanding seems most significant, and most problematic. In this context, the principle of proportionality does not protect the deliberate object of the use of force. This is because LOAC proportionality is secondary to a more fundamental legal rule: military forces (state or non-state) are categorically prohibited from deliberately attacking civilians and/or civilian property.

Thus, if the deliberate object of attack – the person, place, or thing attacked – is not reasonably assessed as a member of the enemy armed forces, a civilian directly participating in hostilities, or an object that qualifies as what the law calls a military objective, launching the attack is unlawful and proportionality is not an issue.

Proportionality in relation to attacks comes into play when an attack is launched (and this includes even a soldier pulling a trigger) against a legitimate target and the attack is anticipated to cause death, injury, or destruction to civilians or civilian objects that are proximate to the intended target.

Incidental injury/collateral damage

Consequently, unlike self-defense proportionality, this variant of the principle in no way protects the legitimate target subjected to attack, for example enemy personnel or objects the enemy is using for military advantage that have thus been transformed into military objectives. It is the risk of what the law defines as, “incidental civilian death, injury, or collateral damage to civilian property” that is the focus of this variant of the rule.

In practice, this means that commanders and other attack decision-makers must balance the value of attacking a target against the “incidental and collateral” consequences of the attack on civilians and civilian property. And while it may seem frustrating, there is simply no mathematical equation at the fulcrum of this balance.

Instead, the rule imposes a test of reasonable judgment: did the person conducting the attack make a reasonable judgment that the value of the attack was not substantially outweighed by the risk to civilians and/or civilian property? In other words, so long as that risk is not assessed as “excessive”, the risk to civilians is considered proportional.

This means that proportionality is not defined by attack outcome, but instead by asking whether the individual launching the attack made a reasonable proportionality assessment when the trigger was pulled. And, unlike the peacetime context, the ultimate test is not whether the anticipated impact on civilians from an attack is slightly greater than the value of the attack – the normal meaning of disproportionate.

As noted, proportionality as a LOAC principle prohibits the attack only if the attacker concludes the incidental or collateral consequences will be excessive to the anticipated concrete military advantage, a term that suggests a much more significant imbalance between military advantage and civilian risk.

The “reasonable commander test”

This reasonable judgment standard is analogous to the test for compliance with proportionality in any context. The legality of a citizen’s use of force in self-defense is properly assessed by asking whether she made a “reasonable” judgment, not whether the level of force used was in fact proportional.

In the context of hostilities, this is often translated into the “reasonable commander” test: was the attack decision one that another reasonable commander, facing the same situation and with the same information available, would have also made? If so, the attack was lawful, even if the result turned out to contradict the expectation at the time it was launched. If not, the attack was unlawful.

Why “effects-based” condemnations are legally invalid

This is why the instinct to rely on “effects-based” condemnations – to condemn an attack as a war crime based only on the civilian harm inflicted by the attack – is legally invalid. And it is also unfair to those who make these difficult judgments.

Relying on effects alone for such condemnation is akin to concluding that 1 plus “I don’t know” equals 10. The “I don’t know” is the military advantage side of the attack judgment equation. Unless that anticipated advantage is considered, attack effects are inherently inconclusive (again, this presupposes the attack was directed against a legitimate military objective. If the effects indicate that the attack was actually directed against civilians or civilian objects, even if the attack fails to produce the intended harm, the attack was unlawful).

Legitimate critique must ultimately focus on the attack decision, and not the attack outcome. As a result, it is near impossible to conclude an attack violated the wartime proportionality rule without considering the situation that informed the attack decision at the time it was made.

This does not mean attack effects are irrelevant. Instead, it means they are only one aspect of a much more complex legality assessment. This may be frustrating, as the full context of an attack decision is often difficult to access or replicate.

But this does not justify a standard of perfect outcomes instead of reasonable judgments, the consequence of treating attack effects not just as relevant, but conclusive proof of illegality.

Ultimately, this also increases the significance of other evidence of good-faith commitment to civilian risk-mitigation efforts during hostilities. From an assessment standpoint, this means there should be greater emphasis on two critical and often objectively verifiable questions:

  1. Was the commander trying to attack a legitimate enemy target, or deliberately attacking civilians?
  2. Did the commander implement all feasible measures – like target verification, warnings, use of precision engagement, and timing of the attack – to mitigate civilian risk?

Concluding observations

How these questions are answered provides a much more credible assessment of respect for the law of armed conflict than simply relying on images of tragic but often unavoidable attack effects.

It also incentivizes commanders and other attack decision-makers constantly try to mitigate civilian risk in ways that will not compromise their legitimate military objectives, even when the enemy tactics are intended to exacerbate that risk.

Sadly, the result of such measures will rarely eliminate all risk, especially when confronting an enemy that deliberately tries to increase civilian risk by hiding among them. But it is a far better touchstone of responsible command and operational legitimacy than that approach too often resulting from an erroneous understanding of proportionality.

Lieutenant Colonel Geoffrey Corn (USA, ret.) is the George R. Killam, Jr. Chair of Criminal Law and Director of the Center for Military Law and Policy at Texas Tech University School of Law. He is also a Distinguished Fellow at the Jewish Institute for National Security of America (JINSA).

Originally Published in Lawfire Blog.