Applying game theory to Syria

International norms tend to dissolve if they are not enforced

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On Aug. 21, several chemical weapons were used against civilians in Syria. Although this is being contested, we are told these chemical weapons were fired by the Syrian government, commanded by President Bashar Assad, against opposition strongholds. The apparent use of chemical weapons by the Syrian government has led President Barack Obama to call for missile strikes.

This push for intervention has led many to ask, why should we intervene in Syria after 1,400 people were killed by chemical weapons when we ignored more than 100,000 civilians deaths by conventional weapons?

The first answer one receives is that Mr. Obama drew a "red line" at the use of chemical weapons. This fact alone is hardly reason to act; I have no interest in preserving Mr. Obama's reputation for drawing lines, red or otherwise.

Undoubtedly a death from chemical weapons is more painful than a death from most other means. But if we want to engage in the morally questionable practice of adding up the "badness" of deaths, it's hard to believe that even 1,400 horrible deaths is worse than 100,000 deaths by other means.

Ultimately, the most persuasive argument for intervention in Syria is that there is an international norm against the use of chemical weapons. This norm is codified in the Geneva protocol and the Chemical Weapons Convention, but the norm goes beyond these legal documents. The international norm represents a standard of behavior that we believe holds for all countries in all situations. The norm even applies to those countries that have refused to sign the treaties.

Unlike many other international norms for governmental behavior, this one appears to be regularly followed. Since World War II, chemical weapons have been used only twice: in the North Yemen civil war and in the Iran-Iraq war. There have been "close calls," where chemical weapons have been used for assassinations and in a terrorist attack in Tokyo. They also have been accidentally released and chemical "agents" like napalm have been used in war. But sticking to the strict definition of chemical weapons deployed in war, one finds it surprising how rarely they have been used.

This is surprising because this international norm requires that governments occasionally act against their own self-interest. Even if chemical weapons might help one side to win a war, we expect those countries to exercise restraint. And in most cases they have.

This international norm is an example of what social scientists call a "social norm." Some social norms are easy to enforce because everyone has a private incentive to follow the norm when it comes up -- given that everyone else will drive on the right side of the road, I would prefer to do so myself. However, some norms, like the norm against chemical weapons, require that individuals sometimes act against their own self-interest. In the case of chemical weapons, they must do so when the consequences might be dire.

One conclusion is consistent across game-theory mathematical models and laboratory experiments: These social norms are very fragile. This is good news when the social norms require people to do morally repugnant things, like the norm of binding young girls' feet in pre-20th century China. However, often that fragility is a problem, because the norms maintain a situation where we all benefit in the long run. Greece is discovering what happens when there isn't a norm in favor of paying one's taxes. And this is the case with the norm against chemical weapons.

One theory posits that people are divided into three groups. Some people only follow the norm because they are afraid of being punished for not following the norm. Others want to follow the norm, but also they don't want to be "suckers." They don't want to follow the norm when their opponents won't either. The third group follows the norm whether or not others do, too.

Most people, these authors claim, fall in the second group; they want to follow the norm, but only on condition that others do as well. There are other theories, but they all have similar conclusions: Norms can evaporate quickly when violations start to mount up.

Many of our social norms are maintained by reputations. If a business cheats you, next time you'll choose not to go back. From the perspective of the business, you are punishing it for violating the norm of honesty. With small businesses, this is usually sufficient to keep even the most underhanded business person in check.

But in war, reputation carries little weight -- at least when both parties are fighting for their very existence. Instead we must rely on the intervention of others in the international community if we are to deter those who would violate the norm when given the chance.

In Syria, if we show that there is no consequence for violating one of the few functioning international norms, it may eventually be destroyed. Those leaders who are following the norm only because of the fear of punishment will try to get away with it. This, in turn, will lead those in the second group -- they would like to follow the norm, but only if it's followed by their opponents -- to use chemical weapons because they fear being taken advantage of by a malicious opponent. Eventually, chemical weapons might again become a common occurrence in war, as they were in World War I.

There remain many important questions regarding Syria. Are we sure the government used the weapons? Why should we be the enforcer? Can we find a different way to enforce the norm? Is enforcing this norm worth other consequences, such as angering Russia or violating international law?

But I think one thing is clear: There is a meaningful distinction in Syria between actions taken before Aug. 21 and those after. The latter represent a violation of an important international norm -- a violation that has important consequences for everyone in the international community, ourselves included, and that, if we do nothing, might well cause the evaporation of an important social norm.


Kevin Zollman is an associate professor of philosophy at Carnegie Mellon University and has published more than 20 peer-reviewed articles on the application of game theory to biology, economics and philosophy (


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