Moral fatigue: The effects of cognitive fatigue on moral reasoning

We report two experiments that show a moral fatigue effect: participants who are fatigued after they have carried out a tiring cognitive task make different moral judgements compared to participants who are not fatigued. Fatigued participants tend to judge that a moral violation is less permissible even though it would have a beneficial effect, such as killing one person to save the lives of five others. The moral fatigue effect occurs when people make a judgement that focuses on the harmful action, killing one person, but not when they make a judgement that focuses on the beneficial outcome, saving the lives of others, as shown in Experiment 1 ( n = 196). It also occurs for judgements about morally good actions, such as jumping onto railway tracks to save a person who has fallen there, as shown in Experiment 2 ( n = 187). The results have implications for alternative explanations of moral reasoning.