LAUSR

Significance Humans have several different ways to decide whether an action is wrong: We might ask whether it causes harm or whether it breaks a rule. Moral psychology attempts to understand the mechanisms that underlie moral judgments. Inspired by theories of “universalization” in moral philosophy, we describe a mechanism that is complementary to existing approaches, demonstrate it in both adults and children, and formalize a precise account of its cognitive mechanisms. Specifically, we show that, when making judgments in novel circumstances, people adopt moral rules that would lead to better consequences if (hypothetically) universalized. Universalization may play a key role in allowing people to construct new moral rules when confronting social dilemmas such as voting and environmental stewardship. To explain why an action is wrong, we sometimes say, “What if everybody did that?” In other words, even if a single person’s behavior is harmless, that behavior may be wrong if it would be harmful once universalized. We formalize the process of universalization in a computational model, test its quantitative predictions in studies of human moral judgment, and distinguish it from alternative models. We show that adults spontaneously make moral judgments consistent with the logic of universalization, and report comparable patterns of judgment in children. We conclude that, alongside other well-characterized mechanisms of moral judgment, such as outcome-based and rule-based thinking, the logic of universalizing holds an important place in our moral minds.