The debate about the justness of Israel’s response to recent attacks by Hezbollah highlights what is, to me, one of the most difficult to understand aspects of Just-War Theory, namely, the criterion of “proportionality.” Proportionality has taken on increased importance in the last centruy or so because of the nature of modern warfare, but that importance doesn’t seem to have been matched with increased precision in understanding and applying it.

To recap: Just War Theory (JWT), at least in its traditional Christian variants, absolutely prohibits the direct targeting of civilians, whether as an end or a means to an end. However, JWT does, under certain circumstances, allow for so-called collateral damage, or the forseen but unintended deaths of civilians. But those deaths must be governed by the criterion of proportionality. In other words, JWT doesn’t license an unlimited number of unintended civilian deaths; those deaths must be “outweighed” by the good effects of the action of which they are a forseen but unintended side-effect. Got that?

The problem is, there’s no generally accepted way of “weighing” the good and bad consequences of a given action and determining if that action does indeed meet the proportionality requirement. People seem to have wildly divergent intuitions about this. In the current case, some people perceive the Israeli actions in Lebanon as an obviously disproportionate response, because it has resulted in the deaths of many innocent civilians, while to others it is a manifestly just response to Hezbollah’s aggression. Granted that not all disputants are working within a just-war framework and prior political commitments are no doubt coloring people’s judgments, it still seems to me that, in the absence of a way to determine proportionality with some precision, such diametrically opposed judgments will continue to be made.

For instance, the Standard Encyclopedia of Philosophy defines proportionality this way:

Soldiers may only use force proportional to the end they seek. They must restrain their force to that amount appropriate to achieving their aim or target. Weapons of mass destruction, for example, are usually seen as being out of proportion to legitimate military ends.

And the United States Catholic Conference puts it this way:

[I]n the conduct of hostilities, efforts must be made to attain military objectives with no more force than is militarily necessary and to avoid disproportionate collateral damage to civilian life and property.

The apparent problem here is that “proportionality” is being defined in ways that are less than informative. How, concretely, do we determine if force is “proportional” or “appropriate” to acheiving its aim? How many civilian deaths, even unintended ones, are permissible in acheiving a given outcome? And how do we figure that out?

At this point JWT has been infiltrated by a kind of consequentialist moral reasoning, with all the difficulties that’s prone to. It’s far from clear that a human life represents a kind of fungible value which is interchangable with some other value. Even if we assume a strict life-for-a-life equivalence, how do we determine how many lives are saved by a given military action? This difficulty is only heightened by the fact that there’s no obvious way of identifying all the consequences of a particular action, which would seem to be necessary in order to determine proportionality. Where do we draw the line, in terms of both time and space?

This doesn’t mean there aren’t some clear-cut examples of disproportionate responses. But a lot of the cases which arise in “post”-modern warfare (involving, for example, “precision” weapons rather than carpet bombing entire cities) seem to fall in that grey area in the middle where clear judgments are hard to come by. Does this point to a fatal flaw in JWT as traditionally conceived, or am I being unduly pessimistic about our ability to make these kinds of judgments?