Secret explosive caches, not Mohamed Atta and company, brought down the Twin Towers. The Bush administration knew the attacks were coming. In fact, the U.S. government itself planned the most devastating terror attack in American history. Or maybe it was Israel...weren't shadowy Israeli "art students" following the 9/11 plotters around all through the summer of 2001?

Five years after the World Trade Center fell and the Pentagon burned, the political, social and, of course, military aftershocks continue. Yet for those who believe that the public never learned the true story behind 9/11, the deeper significance of that day of horror hasn't yet come to light.

Conspiracy theories began circulating before the dust cleared at Ground Zero. Today, the so-called "9/11 Truth Movement"—a disparate band of freelance researchers, videographers, writers, bloggers and secret-plot connoisseurs—remains a vocal, if marginal, force at the fringe of American discourse. In books like 9/11 Revealed and movies like Loose Change, those who don't buy the official story of suicidal Al Qaeda terrorists push a variety of alternative theories.

Where does this strain of thought come from? Do 9/11 conspiracy theories have historical precedents?

Thomas Luckett, a history professor at Portland State University, occasionally teaches a class on the history of conspiracy theories. Luckett, whose specialty is the French Revolution, stresses that he's not a conspiracy theorist himself. "I teach the history of conspiracy theory as a sub-field of European intellectual history," he says. "I tell students that we're not studying conspiracy theories, we're studying people who believe in conspiracy theories."

WW sat down with Luckett on the eve of 9/11's fifth anniversary to talk about where conspiracy theories come from—historically, politically and psychologically.

WW: Most 9/11 conspiracy theories boil down to the conviction that the U.S. government had a hand in planning the attacks. How does that theory compare to conspiracy theories throughout history?

Thomas Luckett: Almost all modern conspiracy theory derives either directly or indirectly from the French Counter-Revolution. There was a group of French counter-revolutionaries—royalists, writing in exile, because otherwise they'd have gotten the guillotine—who wrote a series of books saying, basically, that the French Revolution was planned far in advance. Not only was it planned far in advance, it was planned by a secret cabal of several groups. There were the Enlightenment philosophes, like Voltaire. There were the Freemasons. And then there were the Bavarian Illuminati. Some of these people thought there might have been an even higher group of conspirators, a kind of master group. They tied the conspiracy to the Knights Templar and traced it all the way back to the third century.

How does that stuff relate to conspiracy theories about 9/11—or the JFK assassination, or any other modern event?

What's interesting about conspiracy theories are when they go from being theories about specific events to being general theories of history. It's one thing to say, okay, 9/11 was the result of a conspiracy. It's another to say that history itself is not the product of social forces and events—the sort of things historians study—but is instead engineered by a secret group.

There's a 9/11 book by, interestingly enough, a Frenchman: Thierry Meyssan. It's a really badly written book, but the most interesting chapter to me is the last one. Having argued that the Bush administration planned 9/11, he goes on to argue that the Bush administration itself is controlled by a small right-wing conspiracy that's steadily gained power within the government since the 1950s.

So the idea that a small cabal is secretly steering history is key. Usually the Jews, right?

One thing you do not find in early conspiracy theories, interestingly, is the myth of an "international Jewish conspiracy." There had always been anti-Semitism in Europe, but before the 19th century the Jews were such a persecuted and impoverished group that to suggest they somehow controlled the world would have seemed ridiculous. But then, by the 1830s, within a generation of Jewish emancipation, the Rothschilds were suddenly the richest family in the world, and Disraeli was one of the most powerful politicians. Europeans naturally wondered, "How did they pull that off?" So a new version of conspiracy theory came about—this time, it was claimed that a secret Jewish organization dominated the world's key political and financial institutions.

Did American conspiracy theory start with the John Birch Society in the '50s, or the JFK assassination?

Not at all. In America, the French Revolution conspiracy theory was important in the election of 1798—the Federalists, led by John Adams, accused Thomas Jefferson of being involved with the Revolution conspiracy. In fact, there'd been a lot of conspiracy theory in the Colonies. There was a widespread belief, for example, that British ministers were conspiring to enslave all the white settlers in America, for example.

But by the 1970s and '80s, American historians basically treated conspiracy theories as though they were a thing of the past. Then, in the '90s, there was a huge Renaissance of conspiracy theory—and it started happening before the rise of the Internet, so you can't just blame wacky websites.

So, why? Why do people who live in the so-called Information Age, when you can Google anything, resort to conspiracy theories to explain what's going on?

The common response is to say that conspiracy theories "simplify" history. I actually find most conspiracy theories to be really, really complicated. I think the real reason conspiracy theory endures in general is that it's so flexible. The left has conspiracy theories about the right. The right has conspiracy theories about the left. Catholics believe in Protestant conspiracies, and vice versa. It's also a great way to criticize modernity. How do you criticize democracy, or science? The conspiracy theorist looks at those things and says they're just an illusion—democracy and science are just tools used to manipulate people.

Conspiracy theory tends to flourish among people who find themselves at odds with public opinion. How do you explain public opinion?

Is there an explanation in there as to why so many 9/11 conspiracy theorists are left-wingers?

It's often hard to talk about the difference between right-wing and left-wing conspiracy theories, because there tends to be a lot of overlap. Historically—again, all the way back to the French Revolution—conspiracy has more often than not been right-wing. But it does seem like 9/11 conspiracy is more prevalent on the left. It's probably largely a reaction to the fact that Bush won two elections.

You don't want to reject an election. And you don't want to say, "Yes, we put our ideas before the people, and we lost." So you say that the election itself was illegitimate, because the people were manipulated into voting they way they did.