Although people clearly moralize diverse concerns—including those related to religion, sex, and food—heterogeneity in conceptual definitions is problematic for theory development and make falsification extremely difficult

Gray, Kurt, Nicholas DiMaggio, Chelsea Schein, and Frank Kachanoff. 2021. “What Is 'purity'? Conceptual Murkiness in Moral Psychology.” PsyArXiv. February 3. doi:10.31234/osf.io/vfyut

Abstract: Purity is an important topic in psychology. It has a long history in moral discourse, has helped catalyze paradigm shifts in moral psychology, and is thought to underlie political differences. But what exactly is “purity?” To answer this question, we review the history of purity and then systematically examine 158 psychology papers that define and operationalization (im)purity. In contrast to the many concepts defined by what they are, purity is often understood by what it isn’t—obvious dyadic harm. Because of this “contra”-harm understanding, definitions and operationalizations of purity are quite varied. Acts used to operationalize impurity include taking drugs, eating your sister’s scab, vandalizing a church, wearing unmatched clothes, buying music with sexually explicit lyrics, and having a messy house. This heterogeneity makes purity a “chimera”—an entity composed of various distinct elements. Our review reveals that the “contra-chimera” of purity has 9 different scientific understandings, and that most papers define purity differently from how they operationalize it. Although people clearly moralize diverse concerns—including those related to religion, sex, and food—such heterogeneity in conceptual definitions is problematic for theory development. Shifting definitions of purity provide “theoretical degrees of freedom” that make falsification extremely difficult. Doubts about the coherence and consistency of purity raise questions about key purity-related claims of modern moral psychology, including the nature of political differences and the cognitive foundations of moral judgment.