Are acts of terror always evil? The answer to this question may depend on a rather ill-understood moral principle, invented by Catholic casuists in the middle ages-the doctrine of double effect.
The broadest definition of terrorism is the deliberate killing of non-combatants. That is how Caleb Carr characterises it in The Lessons of Terror. For this he was taken to task in a review by Michael Ignatieff, who insisted that if the slaughter is carried out by "a state army under regular command, as part of a formally declared campaign to defeat another state" then it ought not to be called terrorism. But then in the Nation, Richard Falk complained about the Bush administration's "narrowing of terrorism to apply only to violence by non-state movements and organisations, thereby exempting state violence."
Morally, it does not matter whether the murderers of civilians are wearing uniforms or not. What might be morally relevant, though, is the cause behind the act of terror. If the cause is a bad one-revenge or a war of aggression-then the act of terror is obviously bad. But what if the cause is a good one? Ignatieff cites General Sherman's murderous march through Georgia in the US civil war, which was intended to bring it "to a speedy conclusion." Since Sherman's intention was good, Ignatieff argues, he was not a terrorist. But this ends the debate too hastily, making terrorism evil by definition. The question remains: can the use of terror in a good cause, whether by a state or non-state agents, ever be morally justified?
If the killing of non-combatants were forbidden, then almost any military action would be out of the question. When naval dockyards, munitions factories, and supply lines are bombed, civilian carnage is inevitable. That is where the doctrine of double effect comes in. Though it is wrong to kill innocents deliberately, this doctrine says, it is permissible to attack a military target with the foreknowledge that some non-combatants will die as a side effect. It may even be permissible to bomb a hospital where Hitler is lying ill.
The doctrine of double effect, which can be traced back to Thomas Aquinas' Summa Theologiae, applies to any act that has both good and evil results. By its logic, such an act is morally allowable under two conditions: one, the agent is aiming only at the good effect, the evil effect is not one of his ends, nor is it a means to his ends; and two, the consequences of the act are good on balance, that is, the goodness of the good effect outweighs the evil of the evil effect.
Acts of terror involve the deliberate killing of non-combatants as a means to an end. Thus they are forbidden by condition one. But is this doctrine really valid? Why not leave out intentions and judge the rightness or wrongness of an act by its consequences, the way utilitarians do? Take the bombings of Hiroshima and Nagasaki. Around 200,000 civilians were executed to cow the rulers of Japan into submission. Truman claimed that the alternative, an invasion, would have cost half a million American lives. If he was right (a big "if"), the net savings from these acts of terror amounted to around a quarter of a million lives. Why let scruples about intentions get in the way of that?
There are many moral philosophers who are unhappy with the doctrine of double effect. They think the distinction between directly-intended effects and inevitable side effects is a contrived one. If you ask the terror bomber why he is killing civilians, he will say, "To win a just war." He might even say that he does not need the civilians actually to be dead, but only to be thought to be dead until the war is over, to demoralise the other side. If his victims could be brought back to life after the end of the struggle, he would not object. In this sense, he does not really intend their deaths. To take a different case: if I can kill Saddam Hussein only by shooting him through a human shield, do I intend harm to the innocent shield or not?
A second problem is identifying the class of evil acts that can never be justified by their good effects. Would the doctrine of double effect forbid lying to an innocent person to save a life? Presumably not, but then why does it forbid the deliberate killing of an innocent? Even accepting that killing is far worse than lying, if you can lie to save a life, why can't you kill to save a million lives?
The debate over the doctrine of double effect, though interesting, is mostly moot. It is possible to think up hypothetical cases where an evil act is a means to a disproportionately good outcome-"If you boil this baby, it will save ten lives." But in the real world, acts of terror are rarely efficacious in a good cause (somewhat less rarely in a bad one). That is not surprising. Deliberately killing non-combatants does not weaken an enemy militarily, precisely because they are non-combatants-children, the aged, and so forth. The bombing of civilians both by the Germans and by the British during the second world war seemed to stiffen the sinews of each side. Terror is especially impotent when it comes to fighting terror-witness the sorry experience of the French in Algeria. All of which suggests an empirical counterpart to the doctrine of double effect: to act knavishly in a good cause is to act foolishly.
