I’ve been thinking about Hume lately – specifically, the ethical theory in Treatise of Human Nature. The idea that the grounds for morality is in learned impulses rather than reason is easy enough for an empiricist like me to pick up, but it’s hard to share Hume’s confidence that a moral society is an inevitable result of our nature. Hume thinks that moral laws arise as conventions, meaning regularities of behavior that people follow because, perceiving that others follow them, they have reason to think it is in their best interest to conform. The convention of property, which Hume takes as fundamental, could certainly be propagated in this way, but it’s not too hard to think up other practices that could meet Hume’s definition just as well but that are hardly, by anything like a folk definition, moral. If one perceives that everyone else is carrying a loaded gun, one has a good reason to carry one too. One could argue that this arrangement is not conventional because it doesn’t really serve anyone’s interest, but all it takes is a premise about the virtue of “defending one’s honor” or some such to counter this claim. Without appealing to an inherent goodness in “human nature,” is there any reason to think that people are more likely to form conventions we would think of as moral than they are to conventionalize evil?
We can find some reason to think so in the Twentieth Century’s preeminent philosopher of convention, David Lewis. Using Lewis’s game-theoretical terms, Hume requires that a convention be a Nash equilibrium, a state in which, all else being equal, no agent can make things better for themselves by changing what they do. Lewis goes further than this (at least in Convention) and requires that a convention be what he calls a coordination equilibrium: the outcome cannot improve for anyone as a result of some single person ceasing to conform. It is easy to see that the practice of universal gun-toting does not meet this condition, because if someone refuses to carry a weapon, that is to the benefit of at least those who might want to rob them. In Lewis’s definition, a true convention gives people not only a reason to conform, but a reason to enforce conformity on others. All else being equal, practices that meet this stronger definition should theoretically be more robust than those that don’t. Perhaps, then, it’s no coincidence that we’ve adopted an ethics that tells us to consider the interests of others.