Liberals and conservatives rely on different sets of moral foundations.

How and why do moral judgments vary across the political spectrum? To test moral foundations theory (J. Haidt J. Haidt & C. Joseph, 2004), the authors developed several ways to measure people's use of 5 sets of moral intuitions: Harm/care, Fairness/reciprocity, Ingroup/loyalty, Authority/respect, and Purity/sanctity. Across 4 studies using multiple methods, liberals consistently showed greater endorsement and use of the Harm/care and Fairness/reciprocity foundations compared to the other 3 foundations, whereas conservatives endorsed and used the 5 foundations more equally. This difference was observed in abstract assessments of the moral relevance of foundation-related concerns such as violence or loyalty (Study 1), moral judgments of statements and scenarios (Study 2), "sacredness" reactions to taboo trade-offs (Study 3), and use of foundation-related words in the moral texts of religious sermons (Study 4). These findings help to illuminate the nature and intractability of moral disagreements in the American "culture war."