For years, physics, neuroscience, and psychology have steadily pecked away at the notion of free will by reducing the self to a mechanistic brain. Lab results have yet to convert the masses to a deterministic worldview devoid of personal agency, but what would happen if they did? Would society fall apart? Would we lose motivation, abandon morality, and dance like robots?

A paper in Psychological Science reports that reducing belief in free will makes people more likely to cheat. Students answered 15 test questions, then self-scored and took a dollar per right answer. Those who'd first read statements describing free will as an illusion took home 27 percent more coin. "To resist temptations," explains lead author Kathleen Vohs of the University of Minnesota, "people need to have a sense that they govern their own behaviors."

"Those subjects feel they wouldn't be blameworthy if they did something morally wrong," speculates Joshua Knobe, a philosopher at the University of North Carolina. Don't try the deterministic defense in the courtroom, though—a mistake dubbed "the fundamental psycholegal error" by Stephen Morse, a professor of law and psychiatry at the University of Pennsylvania. "It's the pernicious belief that once you discover a cause for behavior—biological, psychological, sociological, or astrological—somehow the person should be excused," Morse says. "But if causation is an excuse then everyone is excused and no one is responsible."

Does that mean we shouldn't consider mitigating factors—peer pressure, genetics, mental illness, upbringing, the heat of the moment? Not at all. "Even if we have free will, it's the smallest part of what's going on," says David Eagleman, director of Baylor College of Medicine's Initiative on Law, Brains and Behavior. Most of what drives our action is unconscious. "Would you punish a car for having its brakes go bad? You fix it."

Thanks to research on addiction, junkies are seen as unwell rather than simply wicked, but how much further can science soften the blame game? In a study by Knobe and colleague Shaun Nichols, most people said that, as a rule, full moral responsibility was impossible in a deterministic universe. But presented with a hypothetical resident of said universe who torched his family to run off with the secretary, they changed their tune. We have strong emotional instincts to point fingers (and punish).

Vohs says the implications of her paper, which she co-authored with Jonathan Schooler of the University of British Columbia, go beyond moral breaches and extend to all kinds of temptations: Reducing belief in free will might also make people exercise less and drink more. On the other hand, knowing your limitations and the factors that drive your behavior might keep you out of spots where willpower could fail, like your dealer's crib; too much freedom can be imprisoning too. "There's got to be a balancing point," Vohs says.