Prisoner’s Dilemmas are common tragedies. A divorcing husband and wife hire legal barracudas, each fearing the other will take them to the cleaners, while the billable hours drain the marital assets. Enemy nations bust their budgets in an arms race, leaving them both poorer but no safer. Bicycle racers dope their blood and corrupt the sport because otherwise they would be left in the dust by rivals who doped theirs. Everyone crowds a luggage carousel, or stands up at a rock concert, craning for a better view, and no one ends up with a better view.
Many of the dramas of political and economic life may be explained as Prisoner’s Dilemmas with more than two players, where they are called Public Goods games. Everyone in a community benefits from a public good such as a lighthouse, roads, sewers, police, and schools. But they benefit even more if everyone else pays for them and they are free riders—once a lighthouse is built, anyone can see it. In a poignant environmental version called the Tragedy of the Commons, every shepherd has an incentive to add one more sheep to his flock and graze it on the town commons, but when everyone fattens their flock, the grass is grazed faster than it can regrow, and all the sheep starve. Traffic and pollution work the same way: my decision to drive won’t clog the roads or foul the air, just as my decision to take the bus won’t spare them, but when everyone chooses to drive, everyone ends up bumper to bumper on a smoggy freeway. Evading taxes, stinting when the hat is passed, milking a resource to depletion, and resisting public health measures like social distancing and mask-wearing during a pandemic, are other examples of defecting in a Public Goods game: they offer a temptation to those who indulge, a sucker’s payoff to those who contribute and conserve, and a common punishment when everyone defects.
Outside the lab, a commons in a community where everyone knows everyone else can be protected by a multiplayer version of Tit for Tat: any exploiter of a resource becomes a target of gossip, shaming, veiled threats, and discreet vandalism. In larger and more anonymous communities, changes to the payoffs must be made by enforceable contracts and regulations. And so we pay taxes for roads, schools, and a court system, with evaders sent to jail. Ranchers buy grazing permits, and fishers respect limits on their catch, as long as they know they’re being enforced on the other guy, too. Hockey players welcome mandatory helmet rules, which protect their brains without ceding an advantage of comfort and eyesight to their opponents. And economists recommend a carbon tax and investments in clean energy, which reduce the private benefit of emissions and lower the cost of conservation, steering everyone toward the common reward of mutual conservation.
The logic of Prisoner’s Dilemmas and Public Goods undermines anarchism and radical libertarianism, despite the eternal appeal of unfettered freedom. The logic makes it rational to say, “There ought to be a law against what I’m doing.” As Thomas Hobbes put it, the fundamental principle of society is “that a man be willing, when others are so too . . . to lay down this right to all things; and be contented with so much liberty against other men, as he would allow other men against himself.” This social contract does not just embody the moral logic of impartiality. It also removes wicked temptations, sucker’s payoffs, and tragedies of mutual defection.
Bologna 