CHAPTER 1

Introduction

What This Book Is Good For

How do individuals coordinate their actions? Here we consider"coordination problems," in which each person wantsto participate in a group action but only if others also participate.For example, each person might want to take part inan antigovernment protest but only if there are enough totalprotesters to make arrests and police repression unlikely.People most often "solve" coordination problems by communicatingwith each other. Simply receiving a message,however, is not enough to make an individual participate.Because each individual wants to participate only if othersdo, each person must also know that others received a message.For that matter, because each person knows that otherpeople need to be confident that others will participate, eachperson must know that other people know that other peoplehave received a message, and so forth. In other words,knowledge of the message is not enough; what is also requiredis knowledge of others' knowledge, knowledge ofothers' knowledge of others' knowledge, and so on—that is,"common knowledge." To understand how people solve coordinationproblems, we should thus look at social processesthat generate common knowledge. The best examples turnout to be "public rituals," such as public ceremonies, rallies,and media events.

Public rituals can thus be understood as social practicesthat generate common knowledge. For example, public ceremonieshelp maintain social integration and existing systemsof authority; public rallies and demonstrations are also crucialin political and social change. Social integration and politicalchange can both be understood as coordination problems;I am more likely to support an authority or social system,either existing or insurgent, the more others support it.Public rituals, rallies, and ceremonies generate the necessarycommon knowledge. A public ritual is not just about thetransmission of meaning from a central source to each memberof an audience; it is also about letting audience membersknow what other audience members know.

This argument allows specific insights in a wide variety ofsocial phenomena, drawing connections among contexts andscholarly traditions often thought disparate. One explanationof how public ceremonies help sustain a ruler's authorityis through their "content," for example, by creatingmeaningful associations with the sacred. By also consideringthe "publicity" of public ceremonies—in other words, howthey form common knowledge—we gain a new perspectiveon ritual practices such as royal progresses, revolutionaryfestivals, and for example the French Revolution's establishmentof new units of measurement. It is often argued thatpublic ceremonies generate action through heightened emotion;our argument is based on "cold" rationality.

Ritual language is often patterned and repetitive. In termsof simply conveying meaning, this can be understood as providingredundancy, making it more likely that a message getsthrough. But it also seems to be important that listenersthemselves recognize the patterns and repetition. In terms ofcommon knowledge generation, when a person hears somethingrepeated, not only does she get the message, she knowsit is repeated and hence knows that it is more likely thatothers have heard it. Group dancing in rituals can be understoodas allowing individuals to convey meaning to eachother through movement. But group dancing is also an excellentcommon knowledge generator; when dancing, each personknows that everyone else is paying attention, because if aperson were not, the pattern of movement would be immediatelydisrupted.

I then look at examples of people facing each other in circles,as in the kiva, a ritual structure found in prehistoricstructures in the southwestern United States, the seating configurationof various U.S. city halls, and revolutionary festivalsduring the French Revolution. In each of these examples,the circular form was seemingly intended to foster socialunity. But how? Our explanation is based on commonknowledge generation. An inward-facing circle allows maximumeye contact; each person knows that other peopleknow because each person can visually verify that others arepaying attention. I then look at how inward-facing circlesspecifically, and issues of public and private communicationgenerally, appear in the 1954 feature film On the Waterfront.

Buying certain kinds of goods can be a coordination problem;for example, a person might want to see a movie morethe more popular it is. To get people to buy these "coordinationproblem" goods, an advertiser should try to generatecommon knowledge. Historical examples include the "halitosis"campaign for Listerine. More recently, the SuperBowl has become the best common knowledge generator inthe United States recently, and correspondingly, the greatmajority of advertisements on the Super Bowl are for "coordinationproblem" goods. Evidence from regular prime-timetelevision commercials suggests that popular shows are ableto charge advertisers more per viewer for commercial slots,because popular shows better generate common knowledge(when I see a popular show, I know that many others arealso seeing it). Companies that sell "coordination problem"goods tend to advertise on more popular shows and are willingto pay a premium for the common knowledge theygenerate.

The pattern of friendships among a group of people, its"social network," significantly affects its ability to coordinate.One aspect of a network is to what extent its friendshiplinks are "weak" or "strong." In a weak-link network, thefriends of a given person's friends tend not to be that person'sfriends, whereas in a strong-link network, friends offriends tend to be friends. It seems that strong-link networksshould be worse for communication and hence coordinatedaction, because they are more "involuted" and informationtravels more slowly in them; however, empirical studies oftenfind that strong links are better for coordination. We canresolve this puzzle by observing that, even though stronglinks are worse for spreading information, they are better atgenerating common knowledge; because your friends aremore likely to know each other, you are more likely to knowwhat your friends know.

Finally, I consider Jeremy Bentham's "panopticon" prisondesign, in which cells are arranged in a circle around a centralguard tower. Michel Foucault regards the panoptic on asa...