RITE OF EXORCISM
A sacramental by which a duly appointed person, generally a priest, is authorized to use the special power he receives to drive out the evil spirit. Until recently this power had been conferred in the minor order of exorcist. Nevertheless the power could not be used except by a priest who had received the special and express permission from ecclesiastical authority. The Church, in her directives to exorcists, warns them not to be too ready to assume that there is diabolical possession, since there are so many cases of hysteria or other kinds of emotional disorder that may seem to be "possession." Moreover, explicit directives are given on how to deal with ostensibly possessed persons, notably to exercise great care not to be either deceived or intimidated by the evil spirit.
Over the centuries the rite of exorcism has been long and detailed, with a variety of ritual forms, numerous signs of the cross, recitation of psalms, the Athanasian Creed, prayers to St. Michael, use of holy water, and periodic adjurations. Among other formulas, the priest declares, "I adjure you, ancient serpent, by the Judge of the living and the dead, by your Creator, and the Creator of the world, by Him who has power to send you to hell. Depart immediately with fear and with your army of terror. Depart from this servant of God [name], who takes refuge in the bosom of the Church."
Private exorcism, which is the private adjuring of the devil from harming someone, may be performed by any priest, and also by a lay person; for example, by the use of sacramentals such as holy water or by invoking the name of Jesus.