Ours is an ideological moment, so it’s not surprising that the fiftieth anniversary of The Exorcist has occasioned a turf war between traditional and progressive Catholics. Here’s Matthew Walther, whose perspective I usually value for both its incisiveness and pugnaciousness, waxing nostalgic about the movie’s true Catholicism. And then we have Paul Baumann at Commonweal predictably referring to it as “1970s schlock” portraying a benighted religious vision that belongs in the Bronze Age.

Both articles, however, miss the magic of the film.

In the film’s most notorious scene, 12-year-old Regan MacNeil, played by Linda Blair, mutilates herself with a crucifix, bellowing obscenities in a foreign voice. Blair’s stunt double, 29-year-old Eileen Dietz, performed in some of the more lurid shots. When the film was released to international acclaim, a full-on publicity nightmare erupted, with Dietz claiming she wasn’t getting sufficient credit for her role. Naturally, gossip columnists and reporters were eager to know the mechanics behind this particular scene. The film’s director, William Friedkin, himself an incorrigible showman and raconteur, developed what came to be known as the “Felt Forum Speech.”

In this speech, he recounts a show he attended by an illusionist, “the Great Rinaldo,” in which a woman was sawed in half. The spectacle was replete with gushing blood and the smell of formaldehyde. Of course, no beautiful young assistant actually perished in the performance, but the illusionist ended by posing one question to his audience, “All I ask you is, ‘Did the illusion work? Were you convinced?’” The response was a standing ovation. Friedkin concludes, “Now this is a long way of saying to you, ‘Did it work?’ Don’t ask me how or why, but did it work? That’s the only question, as a filmmaker, that I ask the audience.”

Segaloff is in a unique position to bring all of this material together for people who cherish the original film not simply as a cinematic rite of passage for thrillseekers, but also as a genuine work of art.

Is William Friedkin’s The Exorcist an actual horror film, or is it a “supernatural mystery,” as the novel’s author, William Peter Blatty, insisted? Did it scare the daylights out of audiences because of its convincing portrayal of supernatural evil? Or did it unnerve them on a subconscious level with its incisive social commentary during a very turbulent time in American history? All of these questions are intriguing, but the order is wrong. Taking our cues from Friedkin’s Felt Forum Speech, we should first ask, “Does The Exorcist work?” And after 50 years, the answer is a resounding yes.

Nat Segaloff’s The Exorcist Legacy: 50 Years of Fear sets out to explore the film’s magic, offering a veritable treasure trove of information encompassing everything from the details of the actual case on which the story is based to explosive behind-the-scenes dynamics. Segaloff’s book also features detailed explorations of all the sequels, excepting the newly released Exorcist: Believer. (No big loss there.) For those not in the know, The Exorcist: Heretic is so bad it could serve as fodder for the folks at Mystery Science Theater 3000. The Exorcist III is an intriguing entry with William Peter Blatty in the director’s chair this time. And Exorcist: Dominion was directed by none other than Paul Schrader, a fact that ought to raise a few eyebrows.

Having written the biography of William Friedkin in 1990, Segaloff is in a unique position to bring all of this material together for people who cherish the original film not simply as a cinematic rite of passage for thrillseekers, but also as a genuine work of art.

The critic Mark Kermode has long carried a torch for The Exorcist, steadfastly maintaining throughout his influential career that it’s the greatest film ever made. At a recent screening, he made the canny remark that, although the original possession case that inspired the film was almost certainly not the genuine article, it doesn’t matter. What matters is that William Peter Blatty believed it with full sincerity. You might say the original story that appeared in the pages of the Washington Post “worked” for him.

The question of belief in The Exorcist is a complex one. Blatty was a devout Catholic when he wrote the book and his express purpose was to persuade modern readers that if the devil is real, then God and his angels are also real. William Friedkin was an agnostic Jew who saw Blatty’s novel as a literary masterpiece and wanted to make an adaptation that honored the spirit of the original story while making full use of cutting edge cinematic technology.

The two were often at loggerheads on set, however, with Blatty insisting on making the theology clearer while Friedkin shrewdly trimmed it back to keep the story moving. After all, Blatty’s key question was “Are you convinced?,” compared to Friedkin’s more pragmatic concern with whether or not it works. Two priests on a staircase discussing the demonic motivations behind the possession of a little girl can’t really compete with a head rotating 360 degrees and green projectile vomit. In the end, though, both sensibilities are marvelously blended, yielding a horror film of real spiritual depth while Friedkin’s visual style constitutes a deft fusion of realism and surrealism.

There are scenes of clinical detachment, like when we witness Regan suffer a series of excruciating medical tests. The actors were encouraged to speak their lines in their own words. The film thus has an undeniable gravitas. In no way does it feel like a movie. And this sense of sobriety enhances some of the more exotic visuals. Father Karras’s dream sequence is a marvel of unnerving imagery and brilliant sound design. Flashes of the demon’s face (Eileen Dietz again) were inspired by Michel Bouquet’s groundbreaking documentary, Night and Fog, which juxtaposes present-day footage of the verdant Polish countryside with black-and-white shots of the carnage that occurred in the death camps that once stood on that very same spot. The film’s most celebrated shot—the exorcist arriving at the MacNeil home—took its inspiration from René Margritte’s Empire of Light.

Segaloff also parts the curtain to offer minute accounts of how all the special effects were orchestrated and film nerds will relish many of these details. (For example, little did I know that make-up effects legend Rick Baker made his professional entrance into film with this movie.)

Segaloff makes it clear that he doesn’t find Blatty’s argument about supernatural evil proving God’s existence to be persuasive. For my part, I think the argument carries some force, but I must admit that the film works better without too much theological baggage. As Segaloff puts it, “Despite the pyrotechnics, noises, makeup, and CGI, and regardless of what people have come to expect from a movie with the word exorcist in the title, what truly scares them is something they brought with them into the theater: uncertainty.”

There’s a roominess to Friedkin’s film that allows this uncertainty to breathe. After 50 years, we’re still asking, “What if the devil is real after all?” The subject matter may be dark, but follow it far enough and you’ll find light not darkness.