Justice Antonin Scalia and Keyser Soze agree: the greatest trick the devil could ever pull is convincing the world he didn’t exist. Fortunately for them, the devil does not seem to be effectively executing this plan. Some 70 percent of Americans, according to a 2007 Gallup Poll, believe in his existence. This personification of evil has implications beyond the supernatural, influencing how we think about what it means for people to be “pure evil.” And as we prepare to playfully celebrate the wicked and depraved on Halloween night, it’s worth pausing to reflect on some of the psychological and behavioral consequences of these beliefs.

Evil has been defined as taking pleasure in the intentional inflicting of harm on innocent others, and ever since World War II social psychologists have been fascinated by the topic. Many of the formative thinkers in the field — Kurt Lewin, Stanley Milgram , Solomon Asch — were inspired by their experiences with, and observations of, what appeared to most people at the time to be the indisputable incarnation of pure evil. But what many saw as a clear demonstration of unredeemable and deep-seated malice, these researchers interpreted as more, in the words of Hannah Arendt, banal. From Milgram’s famous studies of obedience to Zimbardo’s prison study, psychologists have argued for the roots of evil actions in quite ordinary psychological causes. This grounding of evil in ordinary, as opposed to extraordinary, phenomena have led some to describe the notion of “pure evil” as a myth. A misguided understanding of human nature deriving both from specific socio-cultural traditions as well as a general tendency to understand others’ behavior as a product solely of their essence, their soul, as opposed to a more complicated combination of environmental and individual forces.

The issue of whether “pure evil” exists, however, is separate from what happens to our judgments and our behavior when we believe in its existence. It is this question to which several researchers have recently begun to turn. How can we measure people’s belief in pure evil (BPE) and what consequences does such a belief have on our responses to wrong-doers?

According to this research, one of the central features of BPE is evil’s perceived immutability. Evil people are born evil – they cannot change. Two judgments follow from this perspective: 1) evil people cannot be rehabilitated, and 2) the eradication of evil requires only the eradication of all the evil people. Following this logic, the researchers tested the hypothesis that there would be a relationship between BPE and the desire to aggress towards and punish wrong-doers.

Researchers have found support for this hypothesis across several papers containing multiple studies, and employing diverse methodologies. BPE predicts such effects as: harsher punishments for crimes (e.g. murder, assault, theft), stronger reported support for the death penalty, and decreased support for criminal rehabilitation. Follow-up studies corroborate these findings, showing that BPE also predicts the degree to which participants perceive the world to be dangerous and vile, the perceived need for preemptive military aggression to solve conflicts, and reported support for torture.

Regardless of whether the devil actually exists, belief in the power of human evil seems to have significant and important consequences for how we approach solving problems of real-world wrongdoing. When we see people’s antisocial behavior as the product of an enduring and powerful malice, we see few options beyond a comprehensive and immediate assault on the perpetrators. They cannot be helped, and any attempts to do so would be a waste of time and resources.

But if we accept the message from decades of social psychological research, that at least some instances of violence and malice are not the result of “pure evil” — that otherwise decent individuals can, under certain circumstances, be compelled to commit horrible acts, even atrocities — then the results of these studies serve as an important cautionary tale. The longer we cling to strong beliefs about the existence of pure evil, the more aggressive and antisocial we become. And we may be aggressing towards individuals who are, in fact, “redeemable.” Individuals who are not intrinsically and immutably motivated by the desire to intentionally cause harm to others. That may be the greatest trick the devil has ever pulled.

Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist and regular contributor to NewYorker.com. Gareth is also the series editor of Best American Infographics, and can be reached at garethideas AT gmail.com or Twitter @garethideas.