Gratitude increases third-party punishment.

Third-party punishment occurs when a perpetrator of a transgression is punished by another person who was not directly affected by the transgression (i.e. a third-party). Given gratitude's demonstrated ability to enhance both cooperation and the value people place on future-rewards, its capacity to increase third-party punishment - a phenomenon theorised to increase future cooperative behaviour - was investigated. In two experiments, participants were randomly assigned to experience one of three emotional states (i.e. gratitude, happiness, or neutrality) prior to making decisions about how much of a previous financial endowment they would spend to punish a person who transgressed against another at differing degrees within the context of a dictator game. As expected, punishment expenditures decreased for all participants as a dictator's decision became fairer. Of primary interest, however, participants who felt grateful, as compared to those who felt neutral or happy, engaged in significantly more third-party punishment across dictator splits that were not altruistic in nature.