According to Achen and Bartels, political behavior cannot be adequately explained by reference to individual preference. Individual actors exist within social groups established by characteristics including race, religion, socioeconomic status, and nationality, and these group affiliations define how individuals perceive politics. Rather than making independent evaluations of policies, voters generally utilize the beliefs, loyalties, and viewpoints of the social groups to which they belong. The authors thus regard group identity as the foundation of political behavior.

The authors advance this proposition through both theoretical and empirical approaches. Drawing upon the findings of decades of sociological and psychological research, Achen and Bartels argue that humans are naturally inclined to organize their perceptions of the world into categories labeled “us” versus “them,” and to orient themselves toward specific attitudes based upon these categorizations. Furthermore, even arbitrarily created or minimal group designations can create considerable amounts of loyalty and bias. Social divisions that have existed for centuries and current institutional arrangements reinforce similar inclinations in the context of politics.

Within this paradigm, partisanship emerges as the primary factor defining political identity. Achen and Bartels contend that a person’s party identification functions as more than merely a proxy for policy preferences—it serves as an organizing principle for interpreting information and generating beliefs. As they state, “most people make their party choices based on who they are rather than on what they think” (264). Party affiliation thus becomes an expression of social identity rather than the result of independent ideological reasoning. When individuals affiliate with a party, they generally filter subsequent information through the prism of their partisanship. This process can result in systematic errors of perception, as voters modify their perceptions of policies, candidates, and even factually true conditions to align their beliefs with their partisan identity.

Examples from history and contemporary society illustrate the lasting impact of politics based on social identity. The formation of the New Deal coalition, the conversion of white southern voters’ political allegiance, and the dynamic processes associated with elections today all serve to exemplify the pervasive impact of social identity on voters. Even when campaigns appear to be focused on policy-oriented ideologies (e.g., economic reforms), the authors believe underlying social identity still plays an outsized role. Achen and Bartels assert that identity-based voting is not exceptional; rather, it is the usual way politics is practiced.

This focus on identity generates significant consequences. It indicates that democratic politics is far more concerned with group conflicts and coalitions than with deliberative rationality. To understand this reality, scholars must redirect their focus away from individual voters and toward the social structures that influence voters’ beliefs and behaviors. Achen and Bartels summarize this relationship between identity and belief when they write, “People tend to adopt beliefs, attitudes, and values that reinforce and rationalize their partisan loyalties. But those loyalties, not beliefs or ideologies or policy commitments, are fundamental to understanding how they think and act” (296). They thus conclude that group identity does not merely influence voting behavior, it also shapes the beliefs and attitudes voters come to regard as their own.