Stanford University, 1971. It was a very simple concept: a group of young, healthy, male volunteers were split equally and randomly assigned roles. Half became prisoners, half became wardens; they were placed in a makeshift jail and their actions observed.

Although originally planned to last two weeks, the study was abruptly ended after only six days. Prisoners were behaving in pathological ways, having mental breakdowns and participating in hunger strikes. Guards were acting sadistically, stripping prisoners naked and placing bags over their heads, humiliating them both physically and mentally.

It was important to remember that the prison environment was closely simulated. Realistic cells were created with steel bars instead of doors. Prisoners were arrested without warning, and taken to a police station to be photographed and have their fingerprints taken. They were blindfolded and given a prison ID number to be used at all times. They wore heavy chains, as well as a stocking cap to mimic the loss of individuality and dehumanisation that results from shaving prisoners’ heads.

Guards brandished clubs, wore identical uniforms and mirrored sunglasses to prevent eye contact. They were given no specific training, but were relatively free to create their own set of rules and decide how they thought best to maintain order within the mock prison.

At first, no one took their roles seriously. However, after a ‘rebellion’, the guards were angered and began to devise strategies to control the prisoners; they started harassing and intimidating them, inflicting physical punishment and eventually psychological tactics such as the creation of a ‘privilege cell’ which broke solidarity among prisoners and encouraged distrust. The guards began to control the prisoners entirely, stripping them naked, interrupting their sleep and deciding when they could relieve themselves.

For both groups, the experiment was quickly becoming reality. The guards began to see the prisoners as genuine troublemakers, acting with aggression and taking total control; the prisoners were isolated and troubled. Many showed emotional disturbance, hysterical crying, one even broke out in a psychosomatic rash. Even the researchers had come to think like prison authorities, becoming reluctant to release a mentally unstable prisoner, as they believed he was trying to “con” them.

The study ended when a researcher brought in to conduct interviews with the guards and prisoners questioned the morality of the situation. The abuse of prisoners by guards (when they believed cameras were not recording) had become deplorable. Since then, the study has been criticised as being unethical, and the creator of the study accused of being “sucked in” by his own experiment – particularly as the prisoners were not protected from physical and psychological harm. However, given that the dramatic results were unprecedented, it has been argued that the consent of the participants could never have been fully informed. 

The study illustrated how readily people conform to the social roles they are expected to play. Afterwards, guards were appalled and incredulous at their behaviour; one reported feeling “sick at who [he] had become”. The prisoners described how they had lost their identity and were surprised they had become so submissive. The line between role playing and reality had become completely blurred, and they felt they could not quit.

In 2003, shocking photographs of US soldiers abusing Iraqi prisoners were released. These showed guards posing next to naked prisoners with bags over their heads. Direct parallels have been drawn between this and the Stanford Prison Experiment – Professor Zimbardo, the leader of the study, commented that “the majority of us can be seduced into behaving in ways totally atypical of what we believe we are”. To this day, the question lingers: how can “intelligent, mentally healthy, ‘ordinary’ men” – just college students looking to make some summer money – become "perpetrators of evil" so quickly?