The guards were given no specific training on how to be guards. Instead they were free, within limits, to do whatever they thought was necessary to maintain law and order in the prison and to command the respect of the prisoners. The guards made up their own set of rules, which they then carried into effect under the supervision of Warden David Jaffe, an undergraduate from Stanford University. They were warned, however, of the potential seriousness of their mission and of the possible dangers in the situation they were about to enter, as, of course, are real guards who voluntarily take such a dangerous job.

As with real prisoners, our prisoners expected some harassment, to have their privacy and some of their other civil rights violated while they were in prison, and to get a minimally adequate diet – all part of their informed consent agreement when they volunteered.

This is what one of our guards looked like. All guards were dressed in identical uniforms of khaki, and they carried a whistle around their neck and a billy club borrowed from the police. Guards also wore special sun-glasses, an idea I borrowed from the movie Cool Hand Luke. Mirror sunglasses prevented anyone from seeing their eyes or reading their emotions, and thus helped to further promote their anonymity. We were, of course, studying not only the prisoners but also the guards, who found themselves in a new power-laden role.

We began with nine guards and nine prisoners in our jail. Three guards worked each of three eight-hour shifts, while three prisoners occupied each of the three barren cells around the clock. The remaining guards and prisoners from our sample of 24 were on call in case they were needed. The cells were so small that there was room for only three cots on which the prisoners slept or sat, with room for little else.

Asserting Authority

At 2:30 A.M. the prisoners were rudely awakened from sleep by blasting whistles for the first of many "counts." The counts served the purpose of familiarizing the prisoners with their numbers (counts took place several times each shift and often at night). But more importantly, these events provided a regular occasion for the guards to exercise control over the prisoners. At first, the prisoners were not completely into their roles and did not take the counts too seriously. They were still trying to assert their independence. The guards, too, were feeling out their new roles and were not yet sure how to assert authority over their prisoners. This was the beginning of a series of direct confrontations between the guards and prisoners.

Push-ups were a common form of physical punishment imposed by the guards to punish infractions of the rules or displays of improper attitudes toward the guards or institution. When we saw the guards demand push-ups from the prisoners, we initially thought this was an inappropriate kind of punishment for a prison – a rather juvenile and minimal form of punishment. However, we later learned that push-ups were often used as a form of punishment in Nazi concentration camps, as can be seen in this drawing by a former concentration camp inmate, Alfred Kantor. It's noteworthy that one of our guards also stepped on the prisoners' backs while they did push-ups, or made other prisoners sit or step on the backs of fellow prisoners doing their push-ups.

At first push-ups were not a very aversive form of punishment, but they became more so as the study wore on. Why the change?