Based on a reported case of demoniac possession in the Washington, D.C., area in 1949, William Peter Blatty’s The Exorcist (1971) was his second novel. His other work also examines the question of evil. The Exorcist appeared four years after Ira Levin’s Rosemary’s Baby (1967), which also had demoniac terror as its subject. Together these books revitalized the fantasy-horror genre. They are among the most literate and frightening works of their era. Both books were instant best-sellers and were adapted into equally popular films.

The distinction between the novels by Blatty and Levin is noteworthy. The Exorcist, unlike Rosemary’s Baby, is no horrific account of devil worship. On the contrary, it presents a deeply religious affirmation of life within a modern psychomachia, or warfare between good and evil for possession of a soul. That warfare, however, has changed significantly in a post-Freudian world that has redefined the soul and, more important, what constitutes evil. The damnation of Regan is never at issue: Her body and the ensuing exorcism merely provide the opportunity for the demon’s confrontation with men of faith, particularly the exorcist Lankester Merrin, with whom it previously has battled and lost. In a secularized “God is dead” world, that confrontation appears grotesquely nostalgic: Good and evil apparently have lost all clarity, with humanity now assuming the prerogatives of Satan.

Blatty situates this modern psychomachia in a new age of faith, one in which the rational, scientific mind has for the most part supplanted a theological system of belief and its counterpart, the willful disobedience of God.

As the most fully realized character of the novel, the priest-psychiatrist Damien Karras is both a servant of God and a learned man of science, a man tormented by guilt who struggles to reconcile providential design with the darker recesses of the human mind. Karras becomes the modern Everyman of the psychomachia, caught between rational experience and irrational faith. In attempting to explain to MacNeil why her daughter’s illness is a conflict of mind, not a battle with evil, Karras compares the human body to a massive ocean liner, with brain cells as the crew. One of these cells is the captain, who never knows precisely what the rest of the crew below decks is doing. Karras goes on to explain that when one cell assumes the command against the captain’s wishes, or waking consciousness, mutiny occurs and a dual personality results. MacNeil responds that it almost would be easier to believe in the devil.

Karras metaphor modernizes the biblical mutiny that accounts for Satans fall and the ensuing warfare between good and evil. The unfathomable depths of the human mind, though less easily comprehended, have assumed supernatural powers. MacNeil’s doubts are those of many people: Can evil be reduced to the chaotic intricacies of cells and neurons? The demons possession of Regan demonstrates to Karras that evil can be a force unto itself. His fatal encounter in the exorcism proves that evil affirms the existence of good, while good posits the reality of evil. With that knowledge, the necessity for faith triumphs.