Proportionality in war is not a numbers game

McMahan counts casualties, but that counts only that much in the ethics of war

IDF Spokesperson's Unit / CC BY-SA 3.0

Jeff McMahan is undoubtedly one of the foremost ethicists of our time and a towering figure in the ethics of war, having helped shape an entire school of thought within the so-called 'revisionist' tradition. Yet the more he engages with actual wars and conflicts, the more apparent it becomes that his theory of just war—despite its intellectual elegance—struggles to accommodate the complexities of real-world combat. This tension is especially visible in his recent article, Proportionality and Necessity in Israel's Invasion of Gaza, 2023–2024, in which he contends that Israel's military campaign has been both highly disproportionate and morally unnecessary.

McMahan's framing of the conflict echoes historically unpalatable narratives

What stands out immediately upon first reading is McMahan's regrettably ill-considered framing, which undermines the force of his argument from the outset. He opens his article by asserting that Hamas' war against Israel, taken as a whole, is unjust. Yet, curiously, he also states that Palestinians have legitimate claims of justice against Israel that "in radically different circumstances could together constitute a just cause for war." This claim is perplexing, as McMahan does not clarify what these 'radically different circumstances' might entail. The factual context is that Hamas' political leadership grounds its 'claims of justice' against Israel on principles articulated in its founding covenant, which call for the annihilation of the State of Israel and the extermination of Jews. As McMahan's argument stands, it stretches credulity to conceive of circumstances in which any form of 'justice claims' could serve as a just cause for Palestinians to wage war against Israel.

He concludes his argument in a similarly vague tone, asserting that "the threat to Israel from Hamas could have been largely prevented if, in the past, Israel had fulfilled its duties of justice to the Palestinians." This claim mirrors the ambiguity of his opening, as he views Israel's position as comparable to an innocent person intentionally eliminating the possibility of retreat for a violent aggressor. What, then, are the duties of justice one must fulfill toward a neighbor committed to genocidal aims, in order to earn their restraint and goodwill, to refrain from slaughtering and abducting one's citizens? McMahan, once again, provides no answer.

Within this context, it becomes difficult to interpret McMahan's argument as being advanced in good faith. Instead, his judgmental framing aligns with earlier instances of his blanket condemnation of Israel's military actions as an "onslaught on the civilian population of Gaza," coupled with the assertion that its methods effectively amounted to terroristic tactics. It is evident that McMahan would benefit from exercising greater caution, as his arguments—whether intentionally or not—tread on precariously thin moral ice. His assertion that the "slaughter in Gaza provoked […] the conflicts now beginning between Israel and Hezbollah in Lebanon and Israel and Iran," combined with the problematic framing of his article, reveals not only a flawed grasp of the region's geopolitics and a profound disregard for well-documented intelligence on the intentions of such adversaries but also perpetuates a deeply troubling rhetoric of victim-blaming, insinuating that Jews bear responsibility for their own suffering. This rhetoric evokes longstanding antisemitic tropes, which have historically functioned as post-hoc justifications for anti-Jewish violence.

Necessity: McMahan stumbles between hyper-demandingness and vacuous speculation

In his article, McMahan focuses chiefly on the principle of proportionality, addressing necessity only briefly in his concluding remarks. There, drawing on Daniel Schwartz's work, he introduces what he calls the 'retrospective dimension' of necessity, arguing that a belligerent's earlier choices—which may have foreclosed less harmful alternatives—bear on whether its current use of force is truly necessary. If prior decisions contributed to the constraint of options, the moral burden falls on the belligerent, which may then lack the moral entitlement to pursue even seemingly necessary but more destructive measures, such as full-scale invasion. While Schwartz's account offers a philosophically rich rethinking of necessity, it is open to challenge. It relies heavily on speculative counterfactuals, raising epistemic concerns and introducing ambiguity and moral risk into already complex assessments. Moreover, assigning present obligations based on past failings risks injustice to current innocents and undermines the clarity required for legal application. Though retrospective considerations may have some relevance at the margins, they cannot ground a general principle that prior wrongdoing voids the right to self-defense. The prevailing view in both moral theory and international law remains that self-defense is permissible if it meets the standards of necessity and proportionality at the time the threat arises.

The retrospective argument appears to be McMahan's most compelling point. Unfortunately, in its simplified form, it risks inadvertently reinforcing a deeply troubling implication long associated with one of the most pernicious antisemitic stereotypes—that Jews bear responsibility for their own suffering. The remainder of McMahan's assertions seem largely speculative. His recommendations for what Israel ought to have done—implicitly tied to the 'retrospective dimension' of necessity, such as bolstering border defenses or enhancing intelligence capabilities—lack sufficient grounding in rigorous analysis. Furthermore, his invocation of an exceedingly high threshold for satisfying the necessity requirement further undermines the plausibility of his argument.

Within McMahan's framework, in which killing must be objectively justified in a fact-relative sense, war activity seems almost categorically unjustifiable when his claims are taken to their logical conclusion. For instance, he argues that data suggesting around 1,000 Israelis had been killed as a result of the war by the time of his writing indicates that Hamas would likely have caused fewer casualties if Israel had focused on defensive measures rather than launching a ground operation. While this might hold true in the banal sense that war inevitably increases casualties compared to peacetime, it reduces the necessity requirement to an almost unattainable standard, effectively rendering all wars unjustifiable.

Furthermore, McMahan argues that every Hamas militant killed could lead to the recruitment of many more individuals driven by hatred, making Israel's security situation worse. Again, this argument, while valid in highlighting potential long-term consequences of conflict, sets an impossibly high bar for the necessity requirement. It assumes that any action fueling resentment undermines necessity, which could render any war effort inherently unjustifiable.

While some of McMahan's non-philosophical proposals for alternative security measures—although he clearly lacks any particular credentials to offer them—might be considered reasonable, they ultimately seem to be retrospective reflections. These do not, in a substantive way, dismantle the argument that Israel's war meets the necessity requirement. Instead, they appear once again as speculative judgments made in hindsight, lacking the immediacy and practical applicability necessary for a robust critique of the latter.

Proportionality: Reciprocal relations grant Israel greater moral latitude than McMahan can grasp

McMahan dedicates much of his argument to explaining why Israel's war fails to meet the requirements of proportionality. Yet before delving into proportionality assessments, McMahan offers some intriguing reflections on civilian liability. He begins with the assumption that there exists a general and fairly robust constraint against harming civilians in war. He then observes that, both among the Israeli public and among his academic peers, there is an increasing sentiment that the concept of innocence among Gaza's civilians warrants reconsideration. These civilians, it is argued by some, may no longer be considered innocent and, as such, may be deemed liable to attack or at least to suffer collateral harm.

McMahan contends that the view of shifting innocence among Gaza's civilians is unjustified and leads to implausible consequences. He argues that one key reason behind this shift in perceptions of innocence appears to be the 2006 electoral victory of Hamas in Gaza. According to this view, even those who did not vote for Hamas but continue to accept its leadership are thereby deemed to share responsibility. He finds this reasoning implausible, as it implies that civilians in any nation, including Israel, who exert some degree of influence over their leaders would be morally liable to attack, or at least to collateral harm.

McMahan further explains that Israeli citizens, unlike Gaza's population, have considerably more influence over their government than Gazans have over Hamas. Polls conducted before the war reveal that two-thirds of Gazans expressed little or no trust in Hamas, and nearly half of Gaza's population consists of children. Consequently, McMahan argues that if such reasoning were to be accepted, it would follow that Israeli civilians could be considered morally liable to suffer even greater harms as consequences of actions necessary to prevent the starvation or killing of Gaza's civilian population.

While this reasoning may hold on a principled level, one might question whether the shifting notion of innocence involves more than mere support for one's government. Indeed, it seems more plausible that civilians can become implicated in conflicts through various means beyond political allegiance or voting behavior, thus sharing responsibility and becoming liable to suffer harm as a foreseen but unintended consequence.¹ For example, the extent to which one demonstrates genuine value for innocent life, particularly that of the opposing side, should arguably be considered when determining moral responsibility in war.

In Gaza, numerous civilians have become implicated in, or expressed support for, the events of October 7th through various actions, such as aligning with Hamas combatants, engaging in acts of violence—including killing, rape, and looting—celebrating the atrocities, or aiding in the detention of hostages. Furthermore, the fervent welcome given to Hamas fighters upon their return to Gaza, along with the celebration of the massacre of women and children by many, clearly serves as a stark reflection of the value they place on innocent life.

Other ethical frameworks, such as 'conventionalist' accounts championed by Uwe Steinhoff, provide a more coherent foundation for understanding the reciprocal relations central to the morality of war. Conventionalist accounts assert that widely accepted customs and laws possess moral force and are partly constitutive for the morality of war, with evaluations grounded in principles of reciprocity and fairness. From this perspective, proportionality constraints are to be interpreted as affording Israel greater moral latitude than McMahan appears able to acknowledge. Such an approach posits that rights can be forfeited through the failure to reciprocally recognize the rights of others, including the right to life. Consequently, a party that does not uphold these reciprocal moral obligations may forfeit its right to object to harm. Uwe Steinhoff captures this principle by stating:

"One fundamental element of morality is a principle of reciprocity. It is sometimes expressed in the Golden Rule 'Do unto others as you would have them do unto you,' but is in fact even more plausible and stringent in its negative form, meaning that your moral rights are conditional on your respecting the same rights of others. A murderer has no standing to complain if others do unto him what he is so very willing to do unto others. Likewise, civilians applauding the slaughter of women and children, as many recently did in the Gaza strip, forfeit or at the very least diminish their standing to complain if the opponent refuses to give their lives more weight than they themselves accorded the lives of innocent others. This shifts proportionality restrictions in a way that give more moral latitude to the Israel Defense Forces."

Granted, the fact that someone has no standing to complain about being harmed does not, in itself, justify inflicting harm upon them. However, this understanding alleviates some of the argumentative strain that arises from the need to justify harm based on positive moral reasons.² There are arguably multiple reasons that could justify actions in this context, such as deterrence, the liberation of hostages, and others.

War is not merely another trolley problem, nor is it a numbers game

McMahan then proceeds to elaborate on what he considers to be acceptable thresholds of proportionality, framed, in his view, in a highly charitable interpretation in Israel's favor. He argues that these thresholds can be explored "by comparing only the number of innocent people who are likely to be saved by some act or sequence of acts and the number of innocent people who are likely to be killed as a side effect." His argument, based on this calculus, reveals one of most misleading tendencies within revisionist war ethics: the reliance on examples drawn from domestic self-defense or, even more problematically, highly abstract thought experiments involving some form of 'clean killing.'

McMahan argues that intuitive evidence for a defensible ratio of people killed versus people saved can be found in the trolley problem, in which philosophers have conceptualized highly abstract scenarios, where killing as a side effect would be just barely proportionate and, thus, barely permissible. In these scenarios, a ratio of five saved to one killed seems to serve as a rule of thumb for justifying the killing of innocent individuals. To further his argument, McMahan assumes—for the sake of discussion, despite believing the argument is flawed—that combatants may possess a special relations justification for killing five opposing civilians as a side effect of saving one of their own civilians.

He then applies this ratio by engaging in a series of speculative calculations.³ As an example of a violation of the jus in bello proportionality requirement, McMahan references the rescue of four Israeli hostages from the Nuseirat refugee camp in June 2024. Based on certain assumptions he makes, which he again believes are highly favorable to Israel, he argues that the rescue would result in the death of 37 Palestinian civilians as side effects "of reducing the duration of each adult hostage's captivity and substantially reducing the probability that that hostage would be killed." Since this exceeds the five-to-one ratio considered theoretically morally acceptable—albeit theoretical, as he argues that a special relationship between the state of Israel and its citizens is implausible and leads to outcomes that are overly permissive—he deems the action unjustifiable.

McMahan's argument becomes more convoluted as he seeks to demonstrate Israel's violation of jus ad bellum proportionality. He engages in further speculative calculations, arguing that, assuming the IDF had killed only 24,000 innocent civilians and that Israel has a special relations justification for killing five Gazan civilians for every Israeli civilian it prevents Hamas from killing, the number of Israeli civilians Hamas would have to kill for Israel's actions to be proportionate would be 4,800, while on October 7th, Hamas managed to "kill only 695 Israeli civilians, 373 Israeli security personnel, and 71 foreigners."

This is patently absurd. War is not a numbers game, as McMahan seems to believe. The moral constraints of proportionality cannot be contemplated by introspecting one's intuitions in the armchair, assuming that the transition from peace—or from hypothetical scenarios such as the trolley problem—to war changes nothing at all. Even in domestic contexts, rather subtle changes, such as legal differences, can create significant moral distinctions. For example, while civilians do not have the right to stop a driver for a breath test, police officers possess this entitlement, which hinges on a public authority justification.⁴

Surely, there are considerations central to proportionality assessments that cannot be captured by simplistic domestic analogies, let alone by trolley cases. Some of these, McMahan appears to grasp in principle, yet he approaches them with a troubling naivete that leads to their casual dismissal in the current conflict. For example, when discussing Hamas' embedding of military structures within Gaza's civilian population—recognized by other philosophers such as Michael Walzer as an act that shifts responsibility for civilian deaths from Israel to Hamas—he remarks: "Since Hamas members cannot leave Gaza, which is densely populated with civilians, one wonders where else they can embed themselves." One might suspect that, in McMahan's view, Gaza consists of nothing but an unbroken chain of schools, hospitals, and mosques, if he truly takes his own words seriously. What is perhaps even more troubling about this perspective is that McMahan's implicit proposal to extend a form of immunity to Hamas, given that the population lacks influence over its barbaric leaders, and given that those leaders seek shelter behind the population,⁵ results in a situation where this leadership remains shielded by a veil of civilian immunity, effectively rendering it untouchable by military action.

When analyzed within a framework that recognizes reciprocal relations and widely accepted norms of warfare—and when contextualized beyond the abstractions of a thought experiment to incorporate the complexities of urban warfare, the pursuit of military objectives, and the role of deterrence, which McMahan dismisses somewhat superficially as tactics employed by "various apologists for Israel's war"—it is more plausible to assume that Israel has not come close to exhausting its moral latitude regarding the harm inflicted on Gaza's civilians. The reason why Israel refrains from fully exercising this moral latitude, and has made extraordinary efforts to adhere to its obligations under the law of armed conflict, is that civilized nations and their armed forces strive to rise above a 'race to the bottom,' aspiring instead to uphold principles that extend beyond the mere confines of moral obligation.

From armchairs to encampments: Ethics, war, and the erosion of judgment

In the end, McMahan appears preoccupied with condemning Israel for what he perceives as disproportionate war efforts and the unnecessary infliction of harm on innocents. A charitable interpretation might view this as an effort to maintain coherence within his theory of just war. Yet, in doing so, he highlights the limitations of revisionist war ethics in grappling with the complexities of real-world conflicts. The reliance on armchair philosophical introspection to define universal thresholds for proportionality falls short when confronted with the harsh realities of warfare.

Under different circumstances, this might have constituted an intellectually engaging academic discourse. However, in the current context, where many academic institutions in the West, including McMahan's own, have, at times, become hotbeds of antisemitic rhetoric and agitation, hosted rallies and encampments that openly endorse terrorist propaganda, and created a climate in which Jewish faculty and students often feel unsafe, McMahan's reductive reasoning, which attempts to reduce profound moral complexities to the confines of a trolley problem, is deeply concerning. His disingenuous framing, which echoes historically entrenched libels that unjustly hold Jews responsible for their own suffering, is both indefensible and profoundly shameful.⁶

1. McMahan himself acknowledges this complexity in his book Killing in War, where he contrasts neutral civilians with those who "are known to be supporters of their country's war and to have contributed to it and benefited from it in various ways." In such instances, McMahan concludes that "it is better to kill more unjust civilians as a side effect than to kill fewer nonresponsible civilians as a side effect" (pp.218—221).

2. Steinhoff 2020, pp.231—236.

3. McMahan's approach to analyzing casualty figures is problematic on at least two fronts. First, from the perspective of international humanitarian law, the civilian-combatant distinction does not apply straightforwardly in this case. Hamas militants fail to meet the criteria for lawful combatants, such as bearing a fixed distinctive sign recognizable at a distance, carrying arms openly, and conducting operations in accordance with the laws and customs of war. As Uwe Steinhoff notes: "Israel is not faced with a distinction between combatants and civilians, but between civilians who are liable to attack and those who are not. Civilians 'directly participating in hostilities,' as the legal formulation goes, are liable to attack; that is, they can be intentionally targeted without violating their rights. 'Direct participation' includes civilians producing weapons for 'the war effort' or delivering them to any frontlines or launch sites."

Second, while verifying facts is inherently difficult when relying on warring parties, McMahan appears to place undue trust in Gaza Health Ministry figures, claiming they are "compiled by staff in medical facilities, not by Hamas militants." He conveniently overlooks substantial criticisms of these figures, including allegations that they incorporate natural deaths, rendering them fundamentally unreliable. While McMahan acknowledges that discrepancies between Gaza Health Ministry and IDF figures imply one set must be wrong, he leans toward interpreting the existing data as overly favorable to Israel. To make matters worse, he cites a correspondence by Khatib et al., which has been criticized for citing unreliable sources, gross misrepresentations, errors, and omissions, with the authors later admitting that their figures were 'purely illustrative.'

4. Steinhoff 2020, pp.219—221.

5. As is evident, the term 'human shields'—already a horrific concept—serves as a euphemism for human sacrifice, a deliberate tactic employed by Hamas to orchestrate civilian crises to further their malicious agenda. This reality seems to elude McMahan in his analysis of the extensive network of tunnels beneath Gaza: that civilians' lives were endangered by the deliberate obstruction of their access to shelter and safety, with such provisions reserved solely for Hamas terrorists and their families.

6. I would like to express my gratitude to Prof. Gil Siegal for his insightful and constructive feedback on this article.