This November will mark the 50th anniversary of two events that are of special interest to conspiracy buffs. One is the assassination of President John F. Kennedy, a killing that has spawned dozens of theories about the hidden forces that allegedly carried out the crime. The other is a lecture the historian Richard Hofstadter delivered at Oxford, which Harper's later published under the title "The Paranoid Style in American Politics." Half a century of scholarship has either built on or pushed back against Hofstadter's conclusions, some of which don't hold up very well. But it remains the most widely cited essay on American political paranoia.

Some conspiracies are real, of course, but even a conspiracy theory that is entirely false has truths to tell us about the anxieties and experiences of the people who believe it. More, it tells us something about the ways people perceive the world.

On 9/11, a Brooklyn, N.Y., photographer named Mark Phillips climbed to his roof and snapped photos of the burning World Trade Center, which were then distributed by the Associated Press. Later he learned that people were seeing an unexpected image in one of the photographs. When he examined the picture he saw it, too. "The image I saw was distinct," he later wrote. "Eyes, nose, mouth, horns." There, in the contours of the smoke, he found the face of Satan.

Search online and you'll see still more 9/11 pictures in which people have perceived the shapes of demons. There is no shortage of theories about what the faces mean, from the Christian conspiracist who said they were a glimpse of the devil boasting to the Muslim writer who declared they were a warning from God "that the use of terrorism is never permitted in Islam."

Then there is the explanation I prefer. The faces are the result of apophenia, the process of projecting patterns onto data. More specifically, they are pareidolia, in which those patterns are perceived as meaningful shapes or sounds. It is pareidolia that allows us to see a man in the moon, to hear a satanic incantation when "Stairway to Heaven" is played backward, or to conjure the image of your subconscious choice while taking a Rorschach test. Indeed, pareidolia makes the whole world a Rorschach test. The Web is filled with delightful pareidolia-themed photo sets, in which unexpected forms appear in mountains, pasta, fire, clocks, clouds.

Some people transform their experiences of pareidolia into artworks that others can enjoy. The Spanish surrealist Salvador DalĂ­ called this the critical-paranoiac method. At a lecture in Connecticut in 1934, he illustrated the idea with a slide: a postcard photo of tribesmen in front of a hut. He then showed the same image on its side, and pareidolia did its work: With some priming from the painter, the audience could see an image of a human head. "These more or less accidental ideas Mr. Dali is concentrating upon in his own work," The Hartford Courant reported the next day, "but instead of allowing them to be accidental, he is trying to cultivate them."

That act of cultivation can feel like an act of discovery. A group of scholars learned this in 2010, when they played a game they called The Paranoid Style. The historian Rob MacDougall, who organized the exercise, reported afterward that he started it with "a little briefing on pareidolia and apophenia." Then, after asking each player to pick a well-known historical figure, he "told them we were looking for evidence of the secret conspiracy of vampires that has pulled the strings behind the world for hundreds of years." They found "evidence" of each one's role for or against "the Great Vampire Conspiracy." The aim, MacDougall explained, was to feel the kick of that moment "when the evidence starts to line up all too well with the fantasy you have just concocted, and you skate right up to the edge of believing." He added, "it colors your relationship with 'real' history ever after."

Human beings have a knack not just for finding patterns in chaos but for constructing stories to make sense of events, especially events that scare us. And a conspiracy story is especially enticing because it imagines an intelligence behind the pattern. It doesn't just see a shape in the smoke; it sees a face in the smoke.

We will never stop finding patterns. We will always be capable of jumping to conclusions, particularly when we're dealing with other nations, factions, subcultures or layers of the social hierarchy. And conspiracies, unlike many of the monsters that haunt our folklore, do exist sometimes, so we won't always be wrong to fear them. As long as our species survives, so will political paranoia.

This article originally appeared in The Wall Street Journal.