The omission effect in moral cognition: Toward a functional explanation

Moral judgment involves much more than computations of the expected consequences of behavior. A prime example of the complexity of moral thinking is the frequently replicated finding that violations by omission are judged less morally wrong than violations by commission, holding intentions constant. Here we test a novel hypothesis: Omissions are judged less harshly because they produce little material evidence of wrongdoing. Evidence is crucial because moral accusations are potentially very costly unless supported by others. In our experiments, the omission effect was eliminated when physical evidence showed that an omission was chosen. Perpetrators who "opted out" by pressing a button that would clearly have no causal effects on the victim, rather than rescuing them, were judged as harshly as perpetrators who directly caused death. These results show that, to reduce condemnation, omissions must not only be noncausal, they must also leave little or no material evidence that a choice was made.