People would rather let bad things happen than cause them, especially if someone is watching

"Omissions and commissions come up relatively frequently in everyday life, and we sometimes puzzle over them," says moral psychologist Peter DeScioli of Brandeis University, who conducted the study with John Christner and Robert Kurzban of the University of Pennsylvania. "If a cashier gives you an extra $20 bill at the register, some people think it's okay to keep the money, but many of those people would never just swipe the twenty if the cashier wasn't looking." Psychologists have often thought that this is because the brain makes a mistake; it works through the moral calculations differently when we think about a sin of omission -- not giving the $20 bill back -- versus a sin of commission -- stealing a $20 bill.

But DeScioli and his colleagues suspected otherwise; they thought people were actually making a strategic decision about how to act based on how someone else might judge them. So they set up an experiment that used people recruited through Amazon.com's Mechanical Turk website, which pays people small amounts of money to do tasks. Two or three people were involved in each test. Each time, a "taker" had the option to take part of a dollar away from an "owner" -- or to let a 15-second timer run out, in which case the whole dollar was automatically transferred from the owner to the taker, but with a 15 cent penalty leaving the owner with nothing and the taker with 85 cents. Sometimes a third person was involved, to judge the taker's actions and take money away from them for acting badly; sometimes they weren't.

When the takers knew that someone was judging them, 51 percent of participants let the timer run out, even though this was worse for everyone than taking 90 cents; the owner got nothing (instead of keeping 10 cents) and the taker only got 85 cents (instead of 90). This percentage was significantly greater than the 28 percent who let the timer run out when there was no third person judging them.

And it turned out they were right to do that; the third person judged them more harshly if they outright took the 90 cents than if they let the timer run out and deprived the owner of the whole dollar. So people were more likely to do a bad thing by omission if they knew they could be punished for it.

DeScioli says the work will help psychologists sort out the relationship between conscience -- the moral decisions you make on your own -- and condemnation, the negative judgments made by people who see you act.