In May 2004, we all saw vivid images of young American men and womenengaged in unimaginable forms of torture against civilians they weresupposed to be guarding. The tormentors and the tormented were capturedin an extensive display of digitally documented depravity that thesoldiers themselves had made during their violent escapades. The imagesare of punching, slapping, and kicking detainees; jumping on theirfeet; forcibly arranging naked, hooded prisoners in piles and pyramids;forcing male prisoners to masturbate or simulate fellatio; dragging aprisoner around with a leash tied to his neck; and using unmuzzledattack dogs to frighten prisoners.

I was shocked, but I was not surprised. The media and the “person inthe street” around the globe asked how such evil deeds could beperpetrated by these seven men and women, whom military leaders hadlabeled as “rogue soldiers” and “a few bad apples.” Instead, I wonderedwhat circumstances in that prison cellblock could have tipped thebalance and led even good soldiers to do such bad things.

The reason that I was shocked but not surprised by the images andstories of prisoner abuse in the Abu Ghraib “little shop of horrors”was that, three decades earlier, I had witnessed eerily similar scenesas they unfolded in a project that I directed: naked, shackledprisoners with bags over their heads, guards stepping on prisoners’backs as they did push-ups, guards sexually humiliating prisoners, andprisoners suffering from extreme stress. Some images from my experimentare practically interchangeable with those from Iraq.

Not only had I seen such events, I had been responsible for creatingthe conditions that allowed such abuses to flourish. As the project’sprincipal investigator, I designed the experiment that randomlyassigned normal, healthy, intelligent college students to enact theroles of either guards or prisoners in a realistically simulated prisonsetting where they were to live and work for several weeks. My studentresearch associates and I wanted to understand the dynamics operatingin the psychology of imprisonment.

How do ordinary people adapt to such an institutional setting? Howdo the power differentials between guards and prisoners play out intheir daily interactions? If you put good people in a bad place, do thepeople triumph or does the place corrupt them? Would the violence thatis endemic to most real prisons be absent in a prison filled with goodmiddle-class boys?

The enduring interest in the Stanford Prison Experiment over manydecades comes, I think, from the experiment’s startling revelation of“transformation of character”—of good people suddenly becomingperpetrators of evil as guards or pathologically passive as prisonersin response to situational forces acting on them.

Situational forces mount in power with the introduction of uniforms,costumes, and masks, all disguises of one’s usual appearance thatpromote anonymity and reduce personal accountability. When people feelanonymous in a situation, as if no one is aware of their true identity(and thus that no one probably cares), they can more easily be inducedto behave in antisocial ways.

When all members of a group are in a deindividuated state, theirmental functioning changes: they live in an expanded-present momentthat makes past and future distant and irrelevant. Feelings dominatereason, and action dominates reflection. The usual cognitive andmotivational processes that steer behavior in socially desirable pathsno longer guide people. It becomes as easy to make war as to make love,without considering the consequences.

At Abu Ghraib, MP Chip Frederick recalls, “It was clear that therewas no accountability.” It became the norm for guards to stop wearingtheir full military uniforms while on duty. All around them, mostvisitors and the civilian interrogators came and went unnamed. No onein charge was readily identifiable, and the seemingly endless mass ofprisoners, wearing orange jumpsuits or totally naked, were alsoindistinguishable from one another. It was as extreme a setting forcreating deindividuation as I can imagine.

Dehumanization of prisoners occurred by virtue of their sheernumbers, enforced nakedness, and uniform appearance, as well as by theguards’ inability to understand their language. One night shift MP, KenDavis, later reported how dehumanization had been bred into theirthinking: “As soon as we’d have prisoners come in, sandbags instantlyon their head. They would flexicuff ’em; throw ’em down to the ground;some would be stripped. It was told to all of us, they’re nothing butdogs. . . . You start looking at these people as less than human, andyou start doing things to ’em that you would never dream of.”

The Stanford Prison Experiment relied on deindividuating silverreflecting sunglasses for the guards along with standard military-styleuniforms. The power the guards assumed each time they donned theseuniforms was matched by the powerlessness the prisoners felt in theirwrinkled smocks. Obviously, Abu Ghraib Prison was a far more lethalenvironment than our relatively benign prison at Stanford. However, inboth cases, the worst abuses occurred during the night shift, whenguards felt that the authorities noticed them least. It is reminiscentof Golding’s Lord of the Flies, where supervising grown-ups were absentas the masked marauders created havoc.

We want to believe in the essential, unchanging goodness of people,in their power to resist external pressures. The Stanford PrisonExperiment is a clarion call to abandon simplistic notions of the GoodSelf dominating Bad Situations. We are best able to avoid, challenge,and change negative situational forces only by recognizing theirpotential to “infect us” as they have others who were similarlysituated. This lesson should have been taught repeatedly by thebehavioral transformation of Nazi concentration camp guards, and by thegenocide and atrocities committed in Bosnia, Kosovo, Rwanda, Burundi,and Sudan’s Darfur region.

Any deed that any human being has ever committed, however horrible,is possible for any of us—under the right circumstances. That knowledgedoes not excuse evil; it democratizes it, sharing its blame amongordinary actors rather than declaring it the province of deviants anddespots—of Them but not Us. The primary lesson of the Stanford PrisonExperiment is that situations can lead us to behave in ways we wouldnot, could not, predict possible in advance.