The Problem with Proportionality in War


By Andrew Quist

According to the law of war, militaries may not conduct “an attack which may be expected to cause incidental loss of civilian life . . . which would be excessive in relation to the concrete and direct military advantage anticipated” (Geneva Convention art. 51).

This means that military leaders must conduct a cost-benefit analysis before launching an attack and forgo the mission if too many civilians are likely to be killed. However, as psychologist Paul Slovic and legal scholar Amichai Cohen point out in a new article, “These kinds of deliberations can be short-circuited by an overreliance on gut instinct and emotion, which are susceptible to a number of strong psychological biases.”

These biases include psychic numbing and the prominence effect. Slovic and Cohen write, “On an emotional level, people care greatly about protecting individual lives, something known as the singularity effect. But as the number of deaths increases, ‘psychic numbing’ begins to desensitize them. The life that is so precious when it is the only one at risk feels less important to protect within the context of a larger tragedy. . . .

“Prominence refers to the need to justify and defend one’s decisions. National security interests are a top priority in today’s foreign policy world. Thus, when the possibility to save lives appears to conflict with national security, security almost invariably prevails. It is more defensible to protect the homeland than acting to protect nameless, faceless, foreign lives, no matter their number.”

In order to prevent these biases from resulting actions that cause disproportionate harm to civilians, Slovic and Cohen recommend that military leaders engage in decision analysis techniques meant to lessen the impact of biases, like those recommended by Gregory, Harstone, and Slovic (2018). The lives of civilians depend on it.

Works Cited

Slovic, P., & Cohen, A. (2019, July 3). Trusting gut instincts to decide whether a military action is proportional opens a leader to psychological traps. The Conversation.

Gregory, R., Harstone, M., & Slovic, P. (2018). Improving intervention decisions to prevent genocide: Less muddle, more structure. Genocide Studies and Prevention, 11(3), 109–127. Available at