How do individuals coordinate their actions? Here we consider “coordination problems,” in which each person wants to participate in a group action but only if others also participate. For example, each person might want to take part in an antigovernment protest but only if there are enough total protesters to make arrests and police repression unlikely. People most often “solve” coordination problems by communicating with each other. Simply receiving a message, however, is not enough to make an individual participate. Because each individual wants to participate only if others do, each person must also know that others received a message. For that matter, because each person knows that other people need to be confident that others will participate, each person must know that other people know that other people have received a message, and so forth. In other words, knowledge of the message is not enough; what is also required is knowledge of others’ knowledge, knowledge of others’ knowledge of others’ knowledge, and so on — that is, “common knowledge.” To understand how people solve coordination problems, we should thus look at social processes that generate common knowledge. The best examples turn out to be “public rituals,” such as public ceremonies, rallies, and media events.
Public rituals can thus be understood as social practices that generate common knowledge. For example, public ceremonies help maintain social integration and existing systems of authority; public rallies and demonstrations are also crucial in political and social change. Social integration and political change can both be understood as coordination prob