The threat of moral judgment causes people to cooperate better in groups, reveals a new study from Professor of Sociology Robb Willer and two University of South Carolina professors.

Although traditional sociological research has explored the effect of monetary sanctions on group cooperation — that is, how the promise of individual reward influences group members’ behavior — Willer’s team explored explicit moral judgments to reveal that people who are given the opportunity to judge one another’s moral actions ultimately behave more generously and cohesively as a unit.

This is the first study to compare the effect of “costless” moral judgments versus monetary rewards on group cooperation. Willer found that the effect of moral judgments — whether negative or positive — is far greater in fostering generosity and interpersonal connection.

“People really care about their moral reputation,” Willer told Stanford News. “So just knowing that you could be criticized keeps cooperation going.”

The laboratory study split 54 four-person groups between four scenarios: a control, two variations on monetary sanctions, and one scenario involving moral judgments. Each participant was given a set amount of money at the start of a series of interactive online exercises with their group. As the exercises went on, participants were encouraged to “donate” their money to a central group pool and could “react” with moral judgment or monetary sanctions depending on which scenario they had been assigned to.

Willer found that people were more likely to give moral judgment than monetary sanctions. Furthermore, people tended to give positive judgments and thank one another for donating rather than negatively judge people who did not donate. This in turn led to more contributions from other members.

In contrast, monetary sanctions led to retaliatory action that harmed the group as a whole, Willer and his colleagues explained in their report. Still, Willer and his partners pointed to a “tension between theoretical traditions” that argue for either material or moral sanctions as the only way to encourage cooperation; he emphasized that more research ought to clarify and deepen these findings.

Contact Fiona Kelliher at fionak ‘at’ stanford.edu.