LONDON -- The war in Lebanon has prompted the term "disproportionate force" to be bandied about as if some crystal-clear principle of international law lay behind it, telling us when force is disproportionate and why it is illegal. But combat-related civilian deaths are not enough to say that "disproportionate force" has been used. Nor has that standard, whatever it is, been met if more children die on one side than the other. So what, then, does "disproportionate force" mean, and what is its place in the law of war?

Let's go back to basics. In the domestic law of self-defense, the use of force must always be both necessary and proportionate to the interest being protected. A good example is whether a store owner may shoot looters who are escaping with his goods. If there is no other way to stop the thieves, the use of force is necessary.

But is it proportional? That depends on whether the cost to the looters of being shot so clearly outweighs the value of the stolen goods that the store owner should do nothing, at least at the moment. He always has recourse to the police and the possibility that they might recover the goods. In other words, force becomes disproportionate when the costs of using it are too high.