“Power tends to corrupt,” said Lord Acton, the 19th-century British historian. “Absolute power corrupts absolutely.” His maxim has been vividly illustrated in psychological studies, notably the 1971 Stanford Prison Experiment, which was halted when one group of students arbitrarily assigned to serve as “prison guards” over another group began to abuse their wards.

But new scholarship is bringing fresh subtlety to psychologists’ understanding of when power leads people to take ethical shortcuts—and when it doesn’t. Indeed, for some people, power seems to bring out their best. After all, good people do win elective office, says Katherine A. DeCelles, a professor of management at the University of Toronto, and no few business executives want to do good while doing well. “When you give good people power,” DeCelles says she wondered, are they more able than others “to enact that moral identity, to do what’s right?”