A Palestinian runs in an area damaged in an Israeli airstrike in Gaza City. (Hatem Moussa/AP)

 A few weeks ago, the UN Human Rights Council (UNHRC) released a report alleging that Israel and Hamas committed war crimes during the 50-day conflict last summer in the Gaza Strip. While Israel has acknowledged that many Palestinian civilians were killed as a result of the war, it has denounced the allegations that it intentionally targeted civilians and that civilian casualties were excessive in relation to anticipated military gains. Despite overtly firing rockets at Israeli cities and towns, some Hamas officials claim that they only intended to hit military sites, not civilians.

Whether or not Israel and Hamas are being sincere, their claims reflect a widely accepted view that it is morally worse to intentionally kill civilians than it is to kill them either incidentally or accidentally. But when that moral intuition is written into international law, it can leave civilians exposed rather than protected.

Justifying the killing of civilians

Let me highlight two main problems. First, international law permits states to kill civilians — as long as those killings are proportionate to the anticipated military advantages. An intentional shooting of one civilian is a war crime, yet an airstrike that accidentally kills a much larger number of civilians can be permitted if the military decides their deaths are proportionate. That leaves a lot of power in the hands of military decision-makers. If they decide a target is important enough, they can justify a tremendous amount of civilian death and suffering.

Second, international law can enable “plausible deniability” — intentionally aiming at civilians, but claiming that their deaths are accidental. It can be hard to determine whether military decision-makers intend to kill civilians. They can always misrepresent their motives — or, to be blunt, they can lie.

Indeed, my research, currently in manuscript, shows that although most people believe that intentional killings are morally worse than accidental deaths, states often justify military policies that lead to extensive civilian suffering by claiming that any such civilian casualties are accidental and proportionate. As such, even if Israel and Hamas are sincere in arguing that they only aimed at military targets, their policies nevertheless caused large-scale civilian suffering.

Why, then, should it matter whether Palestinian and Israeli civilians were killed or injured intentionally?

The moral and political history of “I didn’t mean to do it”

The idea that intended killings are a bigger moral problem than incidental deaths has a long history. In his Summa Theologica, Catholic theologian St. Thomas Aquinas claimed that even though it can be morally permissible to kill others unintentionally, it is inherently wrong to intentionally kill innocent people. Later theorists argued that it is only permissible to target military objectives in war—a view reflected in the modern laws of armed conflict.

However, the moral importance we place in intentions (whether we did or did not intend to kill someone) is most likely grounded in the emotional wiring of our brains. Research in neuroscience shows that most people react more strongly to intentional harms that involve personal force than they do to harms that are mere side-effects of otherwise justifiable actions. Harms that are mere side-effects don’t push our emotional buttons in the same way that intended harms do.

But banning “intended” and “disproportionate” killing actually creates legal loopholes that states can use to justify tactics that can, in effect, result in widespread civilian suffering. In fact, states have historically used the distinction between intended and unintended killings to justify rules of war that leave some wiggle room for military decision-making.

When the Additional Protocols to the Geneva Conventions were created in the mid-1970s, many Western states, including the U.S. and Canada, used the language of intentions and proportionality to design laws of war that give combatants significant decision-making discretion. For example, Article 51(2) holds that “the civilian population as such…shall not be made the object of attack.” When this article was discussed, critics argued that the phrasing left a big loophole, allowing for plausible deniability. But the phrasing stayed.

Similar concerns arose with respect to the rule of proportionality, which holds that incidental civilian casualties must not be excessive in relation to anticipated military gains. In the diplomatic negotiations, the International Committee of the Red Cross admitted that “the idea of proportionality called for the exercise of judgment on the part of combatants. It might be open to criticism, since the combatants would have to strike a balance between civilian losses and military advantage; but the two values were not commensurate, as had sometimes been pointed out.”

The United States claimed that “the rule of proportionality was as far as the law could reasonably go. If the element of intent was omitted, the provision might be used to justify trials for accidents or unavoidable damage.” In response, North Vietnam said that even though the “advocates of the principle of proportionality” believed that it would “serve to limit the risks to the civilian population,” others “had pointed out that” it could also “open the door to abuses.”

How many civilian deaths are “proportional” — and who decides?

Outlawing intended killings of civilians while allowing states to expose the civilian population to “proportional” incidental harm makes it difficult to use the law to protect civilians. For example, the U.N. report says that Israel and Hamas killed a disproportionate amount of civilians, and that in some cases they may have intended to kill civilians directly.

With respect to Israel, the report points out that “there are strong indications that” civilian deaths from airstrikes on residential buildings that Israel claimed housed militants “could be disproportionate, and therefore amount to a war crime.”

The operative word here is “could.” Proportionality is a messy concept, primarily because it requires us to make complex trade-offs between civilian deaths and military gains — trade-offs that are inevitably subjective. Israel may not have meant to kill civilians, but according to its own records, it killed quite a lot of them — about 761 people. The UN report counts 1,462 Palestinian civilian casualties — and suggests that those were disproportionate. Israel claims that their deaths were not excessive in relation to the anticipated military gains. However, there are no objective rules for deciding what counts as an “excessive” number of civilian deaths. And yet under international law, had these deaths been intentional, the legal implications would be vastly different.

The UNHRC’s report notes that in some cases, Hamas and other Palestinian groups actually “released statements indicating that they intended to attack Israeli civilians” — clearly prohibited by the laws of armed conflict. But the UN commission can’t be definitive, because in “the vast majority of individual rocket and mortar attacks,” the commission writes, it did not have sufficient “information on the intended targets.” And of course, even if Palestinian groups aimed at military sites, they can argue that the resulting harms were “proportionate” by their accounting. Who then is protected by the focus on what was intended?

By leaving such a large loophole, these rules make it difficult to protect civilians. To strengthen protections for civilians in war, future treaties should focus attention on the overall amount of civilian suffering that military operations cause.

David Traven is a Visiting Assistant Professor of Political Science at Williams College.