Influential and long-standing theory predicts that political disagreement will be a rare event among people who communicate on a frequent basis, but accumulating evidence points to a different conclusion. We have seen that political disagreement is remarkably durable even within closely held networks of political communication. Although communication among interdependent citizens is politically influential, it does not eliminate diversity. This creates a puzzle that we pursue in this chapter and the next: How should we understand the dynamic mechanisms of communication and influence – mechanisms that guide individual decision even as they sustain diversity? Inspired by Axelrod's suggestion that an agent-based model can be a useful tool for “thought experiments” and the clarification of theory, we have used the Swarm simulation tool kit to investigate the formation of discussion networks and implications of theories about persuasion and information exchange. As in previous chapters, we treat communication and influence as interdependent yet separate mechanisms within the same process. Patterns of communication occupy center stage in the present chapter. We consider alternative devices through which political viewpoints and public opinion are communicated. The immediate question becomes, does the structure of communication among citizens account for the survival of diverse political preferences?

The mode of our analysis shifts quite dramatically in this chapter and the next. Prior to this point, our strategy of attack has been to dissect relationships and disassemble groups.