Objective The nature and extent of polarization in the American electorate remains fiercely disputed. This study investigates the depth of ideological and value cleavages in political behavior by examining the influence of adherence to three categories of moral epistemology: premodern (morality is absolute, and stems from the guidance of a supernatural source), modern (morality is absolute, and can be determined through scientific and rational means), and postmodern (morality is nonabsolute, and stems from the subjective values of individuals or groups). Methods Multiple correspondence analysis and multiple regression are used to analyze data from Pew's 2008 U.S. Religious Landscape Survey. Results Premodern adherence exerts a general rightward effect and postmodern adherence exerts a general leftward effect on political attitudes. Among politically attentive respondents, moral epistemology promotes ideological constraint across the economic, social, and foreign policy issue domains. Conclusion These findings indicate that ideological divisions in the American electorate are at least partly reflective of fundamental differences in beliefs about the nature and sources of moral knowledge.