A psychologist explains why—and how—moral views change across different life stages, situations, and historical eras.

We like to believe that moral truths are obvious and unchangeable: cheating is wrong, killing is wrong, slavery is wrong. Yet people have often cheated, killed, and enslaved without regret. The acts that feel glaringly wrong to us in the here and now can seem fine to someone who is younger, or faces different circumstances, or lived a century ago.

Why does morality appear so unstable? The popular explanation is that emotions, self-interest, and social pressure easily divert people from moral concerns because they lack sincere moral commitment. But the evidence shows otherwise. Drawing on studies of young children, adolescents, and adults, Audun Dahl argues that human morality is neither immutable nor capricious, neither fixed nor fickle. Rather, people change their moral views when they believe they have good reasons to—reasons that they can articulate to themselves and would endorse for others.

The science of moral change cannot resolve our ethical dilemmas: it does not tell us what’s morally right or wrong. But it can help us understand why we have moral views in the first place, why those views keep changing, and why moral views that seem obvious to us aren’t obvious to everyone else. Separating moral psychology from moralizing, Between Fixed and Fickle reveals what’s behind our changing agreements and disagreements as we travel toward shared and hard-won moral truths.