The Problem of Purity in Moral Psychology

The idea of "purity" transformed moral psychology. Here, we provide the first systematic review of this concept. Although often discussed as one construct, we reveal ~9 understandings of purity, ranging from respecting God to not eating gross things. This striking heterogeneity arises because purity-unlike other moral constructs-is not understood by what it is but what it isn't: obvious interpersonal harm. This poses many problems for moral psychology and explains why purity lacks convergent and divergent validity and why purity is confounded with politics, religion, weirdness, and perceived harm. Because purity is not a coherent construct, it cannot be a distinct basis of moral judgment or specially tied to disgust. Rather than a specific moral domain, purity is best understood as a loose set of themes in moral rhetoric. These themes are scaffolded on cultural understandings of harm-the broad, pluralistic harm outlined by the Theory of Dyadic Morality.

People are fascinated by morality-how do people make moral judgments and why do liberals and conservatives seem to frequently disagree? "Purity" is one moral concept often discussed when talking about morality-it has been suggested to capture moral differences across politics and to demonstrate the evolutionary roots of morality, especially the role of disgust in moral judgment. However, despite the many books and articles that mention purity, there is no systematic analysis of purity. Here, we review all existing academic articles focused on purity in morality. We find that purity is an especially messy concept that lacks scientific validity. Because it is so poorly defined and inconsistently measured, it should not be invoked to explain our moral minds or political differences.