What criteria do people use to decide that something is morally wrong?  This is a fundamental question in the psychology of morality. Some psychologists believe that there is single answer to this question—that all moral wrongdoings share a single basic property. If you think that all moral judgments are based on a single criterion, you are a moral monist.

Probably the most common form of moral monism is harm-based monism. Harm-based monists think that people see actions as morally wrong when they cause someone harm—in the sense of causing pain or suffering. Hitting someone is seen as wrong because it hurts the person. Infidelity is seen as wrong because it causes your partner pain. Cheating on your taxes is seen as wrong because it makes others who pay taxes suffer.

Different from monists, moral pluralists believe there is not a single answer to the question of what criteria people use to judge something as morally wrong. For moral pluralists, people consider actions as morally wrong for a variety of reasons, many of which do not involve causing harm.

The most prominent form of moral pluralism is Moral Foundations Theory. Moral Foundations Theory claims that there are at least five independent domains or ‘foundations’ that may lead people to think that an action is morally wrong. According to Moral Foundations Theory, an action may be considered to be wrong because: it is harmful, it is unfair or unjust, it shows disloyalty to a group, it is disrespectful to an authority, or it is impure or gross. From the point of view of moral pluralism, these five foundations are importantly distinct and cannot be reduced to a fundamental underlying property, such as harm. For example, according to Moral Foundations Theory, people think that consensual incest between siblings is morally wrong because it is impure or gross, independent of whether they think it also causes harm.

We were interested in this debate between moral monism and pluralism because we had reasons to think that the harm-based version of moral monism is incorrect.  That is, we didn’t think that all moral judgments are based on harm. For one thing, there are plenty of harmful acts that many people approve of because they have some kind of benefit. Military interrogations, harmful experiments on animals, and punishing offenders all cause harm, but many people approve of them. Thus, harm, in the sense of causing others pain or suffering, cannot be fundamental to judgments of wrongdoing.

Based on our past research, we thought that the notion of injustice may be a better foundation for morality than the notion of harm. Our deflationary view of harm proposes that people judge harmful acts that involve injustice as morally wrong. For example, hitting someone is considered wrong when it is seen as unjust, but it would not be considered wrong if you hit someone in self-defense.

We also thought that selfishness is central to people’s concept of injustice. When people think of injustice, they have in mind a selfish action that does not consider everyone’s interests in a situation. Hitting, infidelity, and tax evasion are seen as morally wrong when they involve injustice that arises from selfishness.

Although we thought that injustice is important to people’s sense of wrongdoing, we also had reason to believe that moral pluralism is correct—though not necessarily the version offered by Moral Foundations Theory. This is because people seem to consider actions as morally wrong for reasons other than mere injustice. For example, it is unlikely that people consider consensual incest to be morally wrong because it involves injustice.

To test our ideas about people’s moral judgments, we conducted four studies that examined a wide range of criteria that people use to judge whether an action is wrong.  In our first study, we had research participants think of acts of wrongdoing from their everyday lives. They then rated how wrong these actions were and rated the actions on ten dimensions, which covered ratings of injustice (how unfair, unjust, dishonest, and selfish the action was), harm (causing pain or reducing well-being), disrespect for authority, group disloyalty, and impurity (the degree to which the action was gross or impure). Participants reported a great diversity of acts that they considered to be morally wrong. But, crucially, we found that ratings of injustice dominated people’s moral evaluations of these diverse acts. Ratings of harm were less important.

In subsequent studies, we presented participants from America and Greece a diverse set of ten wrongful acts, which they rated as in Study 1. For both American and Greek samples, injustice ratings had the most far-reaching impact on people’s moral judgments. Interestingly, impurity ratings also made an important contribution. Although harm ratings made an important contribution to judgments of wrongness for some acts, their overall contribution was minimal. Disrespect for authority contributed a little, more so for Greek participants than for Americans. Group disloyalty was not related to participants’ judgments of wrongdoing much at all. The figure below visually represents in an approximate manner the overall contribution of each of the five categories to judgments of wrongdoing.

illustration representing approximate overall contribution of each of the five categories to judgments of wrongdoing

Our findings indicate several things. First, the idea of harm-based monism is clearly incorrect. Second, perceptions of injustice contribute most strongly to people’s judgments of moral wrongdoing.  That said, our findings are more in line with moral pluralism than monism. Although injustice is most important, it was not the only notion guiding judgments of wrongdoing.

Lastly, although moral pluralism seems correct, our results do not support the picture set out by Moral Foundations Theory. Some of the five foundations made little, if any, unique contribution to people’s judgments of wrongdoing. Furthermore, though Moral Foundations Theory does not deny this possibility, our findings highlight that people can view the same action in multiple ways—for example, as involving harm, injustice, and disrespect to authority all at the same time—and each can simultaneously feed into an overall judgment that the act was morally wrong.

For Further Reading

Piazza, J., Sousa, P., Rottman, J., & Syropoulos, S. (2019). Which appraisals are foundational to moral judgment? Harm, injustice, and beyond. Social Psychological and Personality Science, 10(7), 903-913.


Jared Piazza is a lecturer of psychology at Lancaster University. His research focuses on the social-psychological factors influencing the way people approach moral issues and the treatment of animals.

Paulo Sousa is a director of the Institute of Cognition and Culture at Queen’s University Belfast. His research interests include agency, moral psychology, and intergroup conflict as well as their relation to religion.