A variety of techniques practiced since ancient times for casting out evil spirits that supposedly cause mental illness and organic diseases is based on the concept that illness is caused by the invasion of the body by demons and evil spirits.
The action of expelling evil spirits by adjuring them to abandon the person, place, or object that has come under their control. Technically the word exorcism describes a ceremony that is only practiced by the Christian Church to expel demons. But the idea of expelling evil spirits goes back to primitive times when the magical rites and practices of Withchcraft were used; for example, the Bushmen of the Kalahari basin in southern Africa used herbal medicines and communal dances to send away evil spirits in the form of invisible magical slivers of wood that they thought had become attached to members of their tribe, causing them to exhibit abnormal behavior. For such ceremonies to be successful it was necessary for the whole tribe to agree to participate. Anthropologists believe that the custom had the social function of keeping the tribe together and its members on good terms with each other.
In Europe and the Middle East in the early classical period, the practice of expelling evil spirits by means of various set prayers and formulas was common. A few ancient Greek, Roman, and Arabic scholars such as Hippocrates and Plato interpreted mental deviations as natural phenomena, but their ideas did not prevail. With the advent of Christianity, the belief in demons persisted and with that belief came the necessity for exorcism. Jesus exorcised demons with one word and said that this act was a sign of the coming of God’s kingdom; so the Christian tradition grew that exorcisms were always carried out “in His name.” In the first two centuries of the Christian era, the power to exorcise was considered to be a special gift not necessarily bestowed on a cleric, and consequently alchemists and witches vied with those from religious communities for the honor of filling the position. In about 250 C.E., the Roman church took exorcism under its control, appointing a special class of the lower clergy called exorcists to do the job and at the same time carefully regulating it by canon law. The duties of the exorcist included the expelling of ghosts or troubled spirits from haunted houses or haunted places. But more important, they came to include the laying on of hands to purge those possessed by abnormal mental or physical states, especially insanity. To combat what was seen as the devil’s work, specific types of behavior were labeled as sinful, and those possessed were tortured in an effort to exorcise the demons from their bodies.