Exorcism
In Catholic practice the person performing the exorcism, known as an exorcist, is an ordained priest. The exorcist recites prayers according to the rubrics of the rite, and may make use of religious materials such as icons and sacramentals. The exorcist invokes God—specifically the Name of Jesus—as well as members of the Church Triumphant and the Archangel Michael to intervene with the exorcism. According to Catholic understanding, several weekly exorcisms over many years are sometimes required to expel a deeply entrenched demon.
Unclean spirit
Such exorcisms are performed rarely by the 21st-century Western church; the more common exorcism involves the ritual preparation of holy water ("aquae"). The 9th-century Stowe Missal preserves an early Celtic formula as "procul ergo hinc, iubente te, domine, omnis spiritus immundus abscedat" ("Therefore at your bidding, Lord, let every unclean spirit depart far from here"). In a Latin version of "The Blessing of the Waters on the Eve of Epiphany" performed in Rome and recorded at the turn of the 19th–20th centuries, the unclean spirit is commanded "per Deum vivum" ("by the Living God"). The modern Latin rite to exorcize holy water banishes any "pestilent spirit" ("spiritus pestilens") or "corrupting atmosphere" ("corrumpens aura"); see Rituals and uses of holy water.