When democracies seek to protect their citizens against new threats posed by terrorist groups such as Al Qaeda, ISIS, Hamas, and Boko Haram, the old rules — designed for conventional warfare among nations — sometimes become anachronistic. New balances must be struck between preserving people’s civil liberties and protecting them against terrorist violence. As Aharon Barak, the former president of the Supreme Court of Israel — a nation that has confronted this issue over many decades — once put it: “Although a democracy must often fight with one hand tied behind its back, it nonetheless has the upper hand.”

Barak was right on two scores: The commitment to the rule of law constrains democracies in fighting terrorists who have no concern for international law; yet although we must fight terrorism with one hand behind our back, that does not mean that we cannot use the other hand forcefully, effectively, and legally.

Employing military force against terrorists who take hostages, as ISIS does, or use human shields, as Hamas does, raises one of the many difficult challenges currently facing democracies. Others, which I will explore in a series of columns this week, include whether we have struck the proper balance between the need for government surveillance and the right to privacy; whether suspected terrorists who cannot be tried should be detained in places like Guantanamo; whether terrorists should be targeted for assassination; and whether torture is ever justified.


None of these issues is amenable to simple answers. They require nuance and calibration — qualities often lost in the emotional debates engendered by the controversial practices employed against terrorists.

Recent events in Gaza, Syria, Iraq, Afghanistan, and Ukraine forcefully pose the first of these dilemmas. When terrorists attack enemy civilians by using their own civilian population as human shields, how can a democracy properly respond? What is the appropriate moral calculus for a democracy weighing the lives of its civilians against the lives of those innocent civilians being used as human shields by enemy terrorists?

The difficult question of how a democracy should respond to attacks that include human shields was faced by Israel during the recent war in Gaza, challenging its ability both to protect citizens from terrorism and to retain its commitment to the rule of law.

The governing principle of international law is “proportionality,” a widely misunderstood concept. It does not mean that there must be roughly the same number of deaths on both sides of a conflict. It does mean that when an army selects a legitimate military target for attack, knowing that the attack may harm civilians, the number of anticipated casualties must be proportional to the military value of the target. For example, if a low-ranking soldier has taken refuge in a school, hospital, or mosque, and attacking him would risk hundreds of civilian lives, such an attack would be disproportional to the military value of killing the soldier — and would therefore constitute a war crime.


A Palestinian fighter from the armed wing of Hamas gestures inside an underground tunnel in Gaza Aug. 18. REUTERS

If, on the other hand, the target were Osama bin Laden, or the current leader of ISIS, the calculus might be different. Former President Clinton recently implied that he could have gotten bin Laden before the terrorist attacks of 9/11 were carried out, but at the risk of civilian casualties. If Clinton had known that killing bin Laden then would have saved the lives of 3,000 Americans on 9/11 — something that couldn’t have been known with certainty — he might well have ordered the attack, despite the risk to foreign civilians. These are the sorts of difficult moral calculations that are supposed to be made, often in the fog of war, by the rule of proportionality. President Obama or his successor may well have to make similar calculations as the United States and its allies seek to destroy ISIS.

Israel had to engage in a proportionality analysis when it sent ground troops to destroy more than 30 tunnels built by Hamas on the Gaza-Israel border. These “terror tunnels,” which were designed for attacks against Israeli civilians and soldiers, begin in Gaza and end on the Israeli side of the border, making them hard to locate. I was in one of them just days before the recent fighting began. The exit was close to a kindergarten with more than 50 children. Fortunately, a Bedouin tracker discovered an air hole in a field that led the Israeli Army to the tunnel. But dozens of other tunnels could not be found and disabled without the deployment of ground troops on the Gaza side of the border.


Israel knew the location of some of the entrances, thanks to air surveillance. But the entrances had been deliberately placed in mosques, schools, and private homes. The only way to destroy them was by sending ground troops into each tunnel, clearing the areas, and blowing them up.

Israeli officials knew that such a ground incursion would risk the lives of its own soldiers, Hamas fighters, and Palestinian civilians who live in the densely populated areas Hamas had selected as entrance points to the tunnels. It’s a stark choice: Allow the tunnels to remain in operation, thereby risking the lives of its own citizens; or send ground troops into Gaza, warn Palestinians in the area to leave, and then destroy the tunnels, with casualties that would inevitably include Palestinian civilians.

Palestinians attend Friday noon prayer on Aug. 8 beneath the fallen minaret of a Gaza City mosque that was hit by Israeli strikes. Associated Press

Israel opted for the second choice, as most democracies would.


These are the kinds of tragic choices that more democracies can expect to confront. The United States will soon face similar quandaries as it deals with the threat posed by ISIS. Thus far we have been able to target ISIS fighters from the air in open areas, killing some and halting their progress, without endangering civilians. But ISIS has now killed two American journalists whom it took as hostages. Soon it may be hiding its fighters among its hostages and civilians. What will we do then?

There are no easy answers. We must learn to live with complexity, moral ambiguity, and nuance. We must fight back with one hand behind our back, but we must also maintain the upper hand. The terrorists act without conscience, but for us that isn’t an option.

Alan M. Dershowitz is a professor emeritus at Harvard Law School. His newest e-book, “Terror Tunnels: The Case For Israel’s Just War Against Hamas,’’ has just been published.