The 'parts' people play as members of various social groups, e.g parent, child, student, etc. These roles are accompanied by expectations we and others have of what is appropriate behaviour in each role, for example caring, obedient, etc.
1. Prisoners had several procedures to encourage them to identify with their roles, e.g instead of leaving the study prisoners could 'apply for parole'
2. Guards were reminded they had complete power over the prisoners