Thursday, December 8, 2022

Utilitarianism and communication

Alice and Bob are both perfect Bayesian epistemic agents and subjectively perfect utilitarians (i.e., they always do what by their lights maximizes expected utility). Bob is going to Megara. He comes to a crossroads, from which two different paths lead to Megara. On exactly one of these paths there is a man-eating lion and on the other there is nothing special. Alice knows which path has the lion. The above is all shared knowledge for Alice and Bob.

Suppose the lion is on the left path. What should Alice do? Well, if she can, she should bring it about that Bob takes the right path, because doing so would clearly maximize utility. How can she do that? An obvious suggestion: Engage in a conventional behavior indicating a where the lion is, such as pointing left and roaring, or saying “Hail well-met traveler, lest you be eaten, I advise you to avoid the leftward leonine path.”

But I’ve been trying really hard to figure out how is it that such a conventional behavior would indicate to Bob that the lion is on the left path.

If Alice were a typical human being, she would have a habit of using established social conventions to tell the truth about things, except perhaps in exceptional cases (such as the murderer at the door), and so her use of the conventional lion-indicating behavior would correlate with the presence of lions, and would provide Bob with evidence of the presence of lions. But Alice is not a typical human being. She is a subjectively perfect utilitarian. Social convention has no normative force for Alice (or Bob, for that matter). Only utility does.

Similarly, if Bob were a typical human being, he would have a habit of forming his beliefs on the basis of testimony interpreted via established social conventions absent reason to think one is being misinformed, and so Alice’s engaging in conventional left-path lion-indicating behavior would lead Bob to think there is a lion on the left, and hence to go on the right. And while it woudl still be true that social convention has no normative force for Alice, Alice would think have reason to think that Bob follows convention, and for the sake of maximizing utility would suit her behavior to his. But Bob is a perfect Bayesian. He doesn’t form beliefs out of habit. He updates on evidence. And given that Alice is not a typical human being, but a subjectively perfect utilitarian, it is unclear to me why her engaging in the conventional left-path lion-indicating behavior is more evidence for the lion being on the left than for the lion being on the right. For Bob knows that convention carries no normative force for Alice.

Here is a brief way to put it. For Alice and Bob, convention carries no weight except as a predictor of the behavior of convention-bound people, i.e., people who are not subjectively perfect utilitarians. It is shared knowledge between Alice and Bob that neither is convention-bound. So convention is irrelevant to the problem at hand, the problem of getting Bob to avoid the lion. But there is no solution to the problem absent convention or some other tool unavailable to the utilitarian (a natural law theorist might claim that mimicry and pointing are natural indicators).

If the above argument is correct—and I am far from confident of that, since it makes my head spin—then we have an argument that in order for communication to be possible, at least one of the agents must be convention-bound. One way to be convention-bound is to think, in a way utilitarians don’t, that convention provides non-consequentialist reasons. Another way is to be an akratic utilitarian, addicted to following convention. Now, the possibility of communication is essential for the utility of the kinds of social animals that we are. Thus we have an argument that at least some subjective utilitarians will have to become convention-bound, either by getting themselves to believe that convention has normative force or by being akratic.

This is not a refutation of utilitarianism. Utilitarians, following Parfit, are willing to admit that there could be utility maximization reasons to cease to be utilitarian. But it is, nonetheless, really interesting if something as fundamental as communication provides such a reason.

I put this as an issue about communication. But maybe it’s really an issue about communication but coordination. Maybe the literature on repeated games might help in some way.

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