Bullying is a particularly dark aspect of the human psyche to which most teachers will be exposed at some point in their career. Sadism is troubling, particularly among young people, because it indicates a deep understanding of the subtleties of suffering. For example, in war the killing of children in front of their parents is not a random act of brutality - the killers are aware of the importance humans attach to family ties, and of the power of parental protectiveness. By shattering these profound human values, the sadist maximises psychological as well as physical pain.
The Marxist psychoanalyst Erich Fromm called sadism "the conversion of impotence into... omnipotence. The core of sadism... is the passion to have absolute and unrestricted control over a living being."
Sadists commit acts of cruelty when they are stressed and desensitised, and see their victims as a threat. This is an important point because it suggests that, in a way, bullies are "victims" too.
There have been many examples of sadism in Iraq when occupying forces have humiliated local people. They have identified a threat or enemy that has mobilised deep intrapsychic forces. "It is always a simple matter to drag people along, whether it is a democracy, or a fascist dictatorship, or a parliament or a communist dictatorship," said Hermann Goering, commander-in-chief of the Luftwaffe, at the Nuremberg trials. "All you have to do is tell them they are being attacked, and denounce the pacifists for lack of patriotism and exposing the country to danger. It works the same in every country."
Bullies in schools use the same principle when they get others to "rally around" them in persecuting their victims. Once you have a joint defence against an external threat (real or imagined), then something psychologists call "groupthink" - where people feel attachment to a cohesive faction and lose their motivation to realistically appraise alternative courses of action - comes into play. Groupthink is common in school playgrounds because these are areas where children are often cut off from adult surveillance. The solution is to ensure that no child feels isolated.
There are too many forces at work dividing people into "us" and "them", including football supporters, party politics and even fans of rival soaps.
Teachers must help pupils learn how to make friends, not enemies. Children must learn not to join gangs who persecute others so, hopefully, they don't grow up to be sadists.
Dr Raj Persaud is Gresham professor for public understanding of psychiatry, and director of the Centre for Public Engagement, King's College London.
His latest book is The Motivated Mind (Bantam Press). Email: email@example.com