Editor’s note: Professor Adil Haque’s response it published here.

In his essay in these pages calling for an immediate ceasefire in the Israel-Hamas war, Professor Adil Haque argues that Israel’s response to the October 7 terror attacks has violated proportionality in the exercise of national self-defense, and that this meaning of proportionality provides legal support for the ceasefire he advocates. I respectfully disagree with his assessment of the current state of law on the right of self-defense, in particular, the legal understanding of proportionality. But first let’s begin with a brief overview of different areas of international law and how each includes a different concept of proportionality.

I. Different kinds of proportionality

In evaluating legal claims regarding the use of force, proportionality is an important concept with distinct meanings in different contexts.

Law enforcement: Human rights law

Under human rights law, the proportionality rule constrains the permissible level of force exercised by individuals in self-defense, or by law enforcement officers in relation to the immediate threat posed by a subject. By way of analogy to domestic law in the United States, law enforcement use-of-force policies, which implement and interpret relevant court decisions, typically emphasize de-escalation, reasonable threat assessment, and the differentiation between fleeing and charging subjects.

Law of the battlefield: International humanitarian law (jus in bello)

Once an armed conflict commences, opposing forces may employ lethal force as a first resort against legitimate military targets. Proportionality in the law governing conduct in warfare (jus in bello) seeks to mitigate the accompanying unintended-but-foreseeable harm to civilians. Thus international humanitarian law (IHL), or the law of armed conflict, prohibits attacks in which the expected incidental harm to civilian persons or objects “would be excessive in relation to the concrete and direct military advantage anticipated.” Commanders must balance and assess the reasonably forecast proximate harm against the concrete and direct military gain expected, and they must further take “precautions in attack” to exercise “constant care,” avoid preventable errors, and minimize collateral damage. IHL proportionality entails an analysis at the time of attack, and under the circumstances then prevailing, as to how much projected collateral damage is justified by the expected military advantage—even extensive civilian harm is not automatically excessive. The allowable expected incidental harm depends upon the anticipated military advantage, i.e. on the other side of the equation.

Law on resort to military force: Jus ad bellum

In addition to the paradigms of a threat-based force continuum in law-enforcement/peacetime and status-based targeting in the battlespace/wartime, there is yet another discrete legal meaning of proportionality. Under the law governing a State’s initiation of military force (jus ad bellum), the response to an armed attack in self-defense must be both necessary and proportionate. These principles do not appear in the United Nations Charter’s self-defense provision explicitly, but are derived from Just War theory as elements of customary international law. Proportionality in the context of a State’s self-defense does not mean tit-for-tat equivalency of forces, nor does it supersede military doctrine on applying decisive force in war. Rather, taking as a backdrop the general prohibition on the use of military force under international law, the jus ad bellum proportionality requirement limits the magnitude of defensive coercion to what is reasonably necessary to secure the lawful objective. It does not preclude a legitimate war aim of extinguishing the threat, as opposed to merely weakening or delaying it, depending upon the nature and severity of the armed attack that required the resort to self-defense in the first place.

II. Assessing Professor Haque’s account of proportionality

This is why Professor Haque’s analysis mixes up the law as it is (lex lata) with the law that one thinks ought to be (lex ferenda). The key “tell” in this regard is the author’s focus on civilian casualties. Knowing-but-unintentional harm to civilians is a function of IHL proportionality, which is almost exclusively concerned with mitigating collateral injury to civilian persons and objects. Jus ad bellum proportionality, however, is centered on upholding the aforementioned general prohibition on the use of force, such that self-defense is not the exception that swallows the rule. Historically, many aggressors have invoked self-defense to cloak their territorial ambitions, and the necessity and proportionality requirements act as guardrails against an open-ended self-defense loophole to wage aggressive or unprovoked war. Whereas necessity specifies that the resort to coercive force should be a last resort, proportionality confines the measures taken to the defensive objective.

Self-defense proportionality is about the strategic scope of the military response to an attack, which implicates its impact on combatants and noncombatants alike. Unlike IHL proportionality, jus ad bellum proportionality is not exclusively, or primarily, a civilian-centric protective measure. According to the Department of Defense Law of War Manual, “proportionality involves a weighing of the contemplated actions with the justification for taking action.” It states that “the proportionality of the measures taken in self-defense is to be judged according to the nature of the threat being addressed. Force may be used in self-defense, but only to the extent that it is required to repel the armed attack and to restore the security of the party attacked.” In further illustration, the Manual suggests that “assessing the proportionality of measures taken in self-defense may involve considerations of whether an actual or imminent attack is part of an ongoing pattern of attacks or what force is reasonably necessary to discourage future armed attacks or threats thereof.”

(Like Professor Haque, I will sidestep here the question whether the right of self-defense is triggered by attacks from non-state actors, although likely for different reasons. For one thing, the post-9/11 era has shifted the terrain in this debate, at least as a practical matter, with major warfighting States claiming self-defense against non-state actors and at least some international organizations and members of the international community acknowledging it. Second, I can’t say to what extent those who would deny a right of self-defense against non-state actors would effectively limit Israel’s lawful options to Entebbe-like hostage rescue operations and law enforcement raids, but Hamas’s actions, capabilities, and intentions go so far beyond what could conceivably be handled by police tactics that it seems like a fruitless discussion.)

The thrust of Professor Haque’s argument may be based on the uncomfortable realities of IHL’s limitations. He writes that if Israel pursues its war aim of destroying Hamas until ultimate completion or failure, “then there is only so much that IHL can do to limit the total number of Palestinian civilians that the Israeli military will kill, maim, and dispossess.” That is, even if Israeli strikes comply with the law of armed conflict by neither deliberately nor disproportionately attacking noncombatants, the overall war effort itself will continue to bring widespread civilian suffering. As an answer to this tragic feature of war, the author argues that self-defense proportionality involves applying a civilian protective measure “to the military campaign as a whole,” rather than only “to specific attacks.”

Professor Haque presents a principle that he claims is rooted in self-defense proportionality but in reality appears untethered from its actual historical and legal roots: namely, that “a State may not destroy an adversary’s capacity to launch future attacks at grossly disproportionate cost to civilians, whether or not this aim is legitimate in the first place.” To boil it down, what Professor Haque is saying is that even if a State is acting in self-defense with a lawful objective, and even if their forces abide by IHL in military operations, they still have a legal obligation to stop fighting if civilian casualties are too high. What makes this argument so forward-leaning is that the author is not merely saying that responding States have a moral duty to stop fighting, or that they have a strategic or public relations reason to stop fighting, but that there is a legal mandate to do so under jus ad bellum proportionality.

In support of this contention, Professor Haque cites an International Law Association (ILA) report stating that the self-defense proportionality assessment should include “whether the harmful effects of the force taken in self-defense are outweighed by achieving the legitimate aims.” Notably, the ILA report does not specifically mention civilian casualties in this context, since war’s harmful effects apply across the military-civilian spectrum. The idea articulated by the ILA is underspecified for a reason. There is no metric or settled legal vocabulary for weighing military war aims with civilian harm, because that is not the law.  As Marty Lederman wrote, “It’s deeply misleading for Adil to assert that this is already an established customary law requirement. Indeed, few if any states have confirmed it (which is why the cited ILA Committee Report doesn’t cite any such authority).” Finally, it may be worth pointing out that the ILA is not a law-making entity and that its Use of Force Committee, for all its impeccably credentialed members, has been wrong before, as when it sought to apply an intensity test to international armed conflict.

Ultimately, claiming that self-defense proportionality compels Israel to “either accept an immediate ceasefire, or drastically narrow its war aims and dramatically change its tactics” due to civilian casualties may operate in the realm of policy advocacy but not legal advice based on existing international law. Whereas Professor Haque contends that the position of those calling for a ceasefire “is morally compelling but legally incomplete”—and that the “invocation of proportionality” would make their stance stronger by resting “it on legal as well as moral grounds”—I would say the opposite: overstating or misstating the law undermines moral and policy arguments rather than buttressing them.

I imagine that Professor Haque might counter that I am taking “a purely instrumental conception of proportionality” and am one of those who “argue that proportionality limits armed force to the kind and degree required to repel an attack, but does not require any proportion between civilian harm and defensive benefit.” However, the normative argument I am making is not about any preferred conception of self-defense proportionality, but rather about the value of a clear-eyed view of ad bellum and in bello legal principles, even (or perhaps especially) in emotionally fraught and historically complex contexts. In the long run, those legal norms, along with the integrity of their definitions, actually do prevent wars as well as save lives in wars—as difficult as that may be to imagine amidst current events. Misinterpreting foundational principles, even if informed by moral urgency, in ways that no State under severe attack would abide can do more harm than good.

In that vein, Professor Haque might also respond that the traditional definition of self-defense proportionality gives carte blanche to States to wage boundless defensive wars. However, the jus ad bellum requirement of proportionality, interpreted faithfully, does constrain States’ defensive options in the wake of an armed attack by tying their war aims to the nature of the threat they face. For some commentators, this limit may be insufficient, but that does not mean it is not real.

Based solely on a calculation of overall population in relation to number of terror victims, October 7, 2023 was the equivalent of roughly fifteen 9/11s at once. In response to that earlier attack, the United States launched a multi-decade, geographically-unbounded Global War on Terrorism. The point here is in no way to play a morbid numbers game comparing victims of terrorism and those of State responses to it, nor is it to overlook that there were and are many vehement objections to the legal framework underlying U.S. counterterrorism operations over the last twenty-two years. Recent history, however, provides at least some insight into the untenability of a rigid new legal requirement for State victims of terror to eschew a war aim of eradicating capable, motivated, and persistent threats due to overall civilian harm, often exacerbated by the terrorist groups themselves. Rather, States’ legal obligations remain constant: first, to resort to self-defense only as a last resort and in proportion to the threat faced; and second, to adhere to IHL in any ensuing armed conflict. Whether the magnitude of State responses to terror is ethical and wise goes beyond determinations of legal compliance.

IMAGE: Palestinian families walk past destroyed buildings in Bureij, in the central of Gaza Strip, on November 14, 2023, amid the ongoing battles between Israel and the Palestinian group Hamas. (Photo by MOHAMMED ABED/AFP via Getty Images)