The Syrian government appears to have violated the Geneva Protocol to the Hague Convention (1925). The Protocol, which Syria signed in 1968, begins: “the use in war of asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices, has been justly condemned by the general opinion of the civilised world.” And so it should be.

Citing this rule as a justification for a bombing campaign would be a classic example of legalistic reasoning. I do not mean “legalistic” in a pejorative sense. The best argument for intervening in Syria is to enforce the Geneva Protocol, and it is an example of legalistic reasoning for three reasons:

1. It draws a bright line in one particular place. Conventional bombs or even machetes could kill more innocent people than poison gas did in this case. Likewise, you may hurt someone worse by insulting him than by robbing his store. But a law establishes very general prohibitions in order to control evils, to prevent wrongs from escalating, to allow people the freedom to do things not expressly forbidden, and to create a structure of predictable norms and consequences. Robbery is forbidden; so is the use of chemical weapons. Neither rule guarantees justice or peace, but they do create a worthwhile structure.

2. Deciding whether the rule was violated is different from evaluating how much damage was done or how much good would be achieved by punishing the violator. Legal reasoning puts consequences and persons largely aside. The rule of law is honored when no one violates the law or when all violations are predictably punished.

3. The expressive aspect is important. Law is not just about making things better; it is about expressing norms. A jury exists in part to represent the community and express the community’s view in the form of a verdict stated in open court. Likewise, the Geneva Convention speaks of “the general opinion of the civilised world.”

I think the agreement to ban chemical weapons was an achievement, even though it did not prevent many other (or even worse) evils. Violating that agreement should bring condemnation and punishment. If Bashar Assad can use chemical weapons with impunity, that is a sad day. I don’t think a meaningful punishment would have to end Assad’s regime, any more than a punishment for robbery must so bad that no one ever robs again.

Nevertheless, a legalistic framework does not support the US and allies bombing Syrian military installations. That is because:

1. The punishment would not fall on the perpetrators. We talk about “bombing Syria” or even “bombing Assad.” We would actually kill individual human beings who were present in Syria when the bombs dropped. Bashar Assad is very unlikely to be one of those individuals, and “Syria” is not something that can suffer. Using these proper names is a disingenuous form of synecdoche. The more accurate sentence would be: “Assad ordered chemical weapons to be used, so we must kill some other people.” Put that way, it is a clear injustice.

2. The punishers would not have standing to judge. It is deeply unfortunate that the UN won’t decide to punish Bashar Assad for using chemical weapons. But it won’t, and unilateral action by the US would not restore the principle of rule of law. It is as if A robbed B’s store, the police did nothing, and so C beat up A. That is not an advance for justice. C’s beating up A could have positive consequences. For instance, it might cause A to cease robbing people. But once we are in the realm of weighing consequences, the calculus probably does not favor a US bombing campaign in Syria.

3. The expressive aspect of the case would be ambiguous. What norms would a US-led bombing campaign express? Never use poison gas? (Maybe.) Go ahead and use poison gas because the cost is not very high? (Perhaps.) The US and European countries that previously ruled the Middle East can bomb anyone they like? (Maybe.) The expressive function of the law requires very carefully designed expressive institutions, such as public jury trials in courts of law. Otherwise, the act of A punishing B just looks like violence.

In short, the best argument for a bombing campaign in Syria is legalistic, but it fails.