Tuesday, March 1, 2022

The probability of success condition for a just war

Traditional just war theory holds that a necessary condition for a just war is not just the proportionality condition that the expected benefits exceed the expected harms, but that success is likely.

In typical cases, where the success condition fails, the proportionality condition fails as well. However, there are some hightly hypothetical cases where the success condition fails but the proportionality condition is satisfied. And in those cases I think war is justified. Thus, we should drop the success condition, and simply insist on proportionality, while being clear that proportionality includes a probabilistic assessment.

Case one. Kneebonia has exactly one missile and no weapons other than that missile. They declare war and shoot that missile at a gorgeous cathedral in the Elbonian capital that took centuries to build. They offer the Elbonia the following terms of surrender: Elbonia will become a province of Kneebonia and all books in the Elbonian language will be burned and permanently banned. Elbonia has one soldier. They parachute her onto the roof of the Kneebonian missile control building, and task her with penetrating to the computer room in order to redirect the missile into the sea. However, they know that the chance of success in this mission is 1%, because she is likely to be captured. At the same time, because the Kneebonian soldiers have no weapon other than the missile, one can be pretty confident that even if the mission fails, the Elbonian soldier will survive.

The Elbonians reciprocate the declaration of war and send their one soldier in. Proportionality may well be met: the danger of one soldier being non-lethally captured is proportionate to a 1% chance of saving a precious cultural artifact that took centuries to build. But the chance of success in this war is 1%. But if there is no success, there will be likely very little harm (one soldier captured alive).

Granted, this is a defensive case. But there are offensive cases that can be imagined as well.

Case two. A regional branch of the Elbonian army is perpetrating genocide on local Kneebonian minorities. Kneebonia has only one missile, and it can shoot it at the headquarters of that branch. Intelligence data shows that if the missile strike is successful, Elbonia will surrender and agree to end the genocide. However, the missile is wonky. There is a 99% chance that instead of hitting the headquarters, it will veer off-course and explode unseen in Elbonian coastal waters, and there is a 1% chance of success. Intelligence data shows that in case of a miss Elbonia can simply withdraw its declaration of war and the war will end, with the Kneebonians slightly puzzled as to why no hostile action apparently occurred.

Again, the probability of success is 1%. Yet it seems that war is justified. Again, if there is no success, there will be no harm.

All that said, the probability of success condition is a useful heuristic. For in typical wars, where there is insufficient probability of success, the expected harms will outweigh the expected benefits.


Brandon said...

I think this argument is essentially right.

An independent, and perhaps more controversial, reason to think that 'probability of success' should not be a universal consideration for just war, even if it may be a common one. I think it can be argued that the earlier forms of traditional just war theory were structured not as a list of criteria but as a general means-end analysis -- for warring (since it was originally thought of as an action rather than a state of war) to be just, its end and means have to be just. Lawful authority and just cause are considerations you need to assess ends (warring occurring under the ends to which lawful authority is ordered, for instance); proportionality, or appropriateness to ends, is what you are primarily assessing when assessing means, and all the other criteria are just things that are relevant to proportionality. But at some point, it seems to be that people discussing the criteria lost recognition of the fact that you are not just following an arbitrary list but doing a means-end analysis. In the original, you have analogues of just war criteria for every kind of organized activity that can be just, because in all such cases you have to assess ends and means. It would be really odd, though, to argue that 'probability of success' is a criterion for justice for every such kind of activity (although perhaps 'possibility of success', which I think is what we find in the Salamancans, would be).

Tomasz M. said...

I would tend to think that it comes down to whether one can really compare all the expected harms and benefits. In simple cases, whenever one can easily compare her available options in a decision-theoretic model, the success condition might be dispensed with because the probability of success is already involved in calculations.
However, in a more realistic setting, when ignorance with respect to the expected consequences of the war is involved, it might be crucial to rely on the success condition.

For example, suppose that in case one, the intelligence data warns that even though it is very unlikely that Kneebonians will intensify their hostile persecution after capturing the Elbonian soldier, it is unknown how they will really react. In short, if there is no success, most probably there will be very little harm. But it is not certain, and in the worst case scenario the harm might be very significant.
In this case, it would seem to me that the proportionality condition is still met (because the expected benefits outweigh the expected known harms). Yet, I am not sure that in such poor success conditions with the ignorance of the consequences of the failure, it would be prudent to reciprocate the declaration of war.