Conspiracy theories are articles of faith for the masses in an age of unbelief. You will have had the same experience as me on numerous painful occasions: a perfectly ordinary exchange with someone about current political events suddenly veers off-piste and disappears down a crevasse yawning with credulousness. "Everyone knows," your interlocutor asserts, "that Princess Di was assassinated by MI5 to stop her having a Muslim baby . . . that the September 11 attacks were mounted by the Bush government to provide a pretext for their Iraq oil-grabbing venture . . . that global warming is a fiction devised by the scientific establishment in order to stop us enjoying our city breaks . . ."

It's altogether pointless trying to winch these people out of their crevasse with a thin cable of reason, because they've already made the brave leap into believing something for which there is no real empirical basis whatsoever. Indeed, if you do challenge them along these lines, they simply turn
on you with words to the effect that you cannot prove your version of these events, while they, at least, are maintaining a healthy scepticism - the implication being that you're merely another dupe.

You've been jihad

What got me thinking about the collective insanity of the conspiratorial laity - besides running into it almost every day - was the experience of a young friend of mine who is studying philosophy at a perfectly respectable university. She was given by her tutor the assignment of watching on YouTube a "documentary" called Loose Change. This, for those of you fortunate enough not to have seen it, is a series of "facts" and "observations" that, taken together, are intended to support one of the "arguments" above; namely, that it wasn't a group of Islamist jihadists who engineered the destruction of the twin towers and the attack on the Pentagon, but elements within the federal government itself who conspired to take the lives of thousands of their own citizens.

When my young friend taxed her tutor with the ridiculousness of this thesis, she was told that watching Loose Change was integral to her study of Hume's Enquiry Concerning Human Understanding.

That the September 11 attacks should have generated so much conspiratorial guff is woefully predictable. Loose Change is only a wilder and more explicit version of the thesis bruited by Michael Moore's asinine Fahrenheit 9/11. In that feature-length exercise in infantile tendentiousness, Moore made great play of the connections between the Bin Laden and Bush families, hinting that these were causally implicated in the attacks. The truth is that it would be surprising if the Bin Ladens - whose vast construction company is by appointment to the House of Saud - didn't hobnob with the Bushes.

We're history

There are some genuine conspiracies afoot in the world. These tend to be restricted in their ambit; all too often they cock up spectacularly. But with the large-scale events where the credulous see conspiracy, cock-up is invariably the correct explanation. Princess Di's death? A drunken cock-up. The British invasion of Iraq? An arrogant cock-up by those swinging dicks Blair, Campbell et al. Global warming? A cock-up by most of humanity. So on it goes: cock-up, cock-up, cock-up. Contrary to what Marxists and conspiracy theorists alike believe, human history doesn't advance by any discernible dialectic, but revolves in a cycle of cock-ups. Presumably, this will continue until the gyre widens out into the big cock-up that does for us all entirely.

It's easy to understand why conspiracy theories should have such a grip on the collective imagination. It's tough living in a chaotic universe ruled only by contingency and cock-up, and without the reassuring belief that all is for the best in the best of all possible worlds. Besides, the conspiracy-believer is flattered by his own credulousness, which he mistakes for enhanced insight. He - unlike you - is in on something, privy to the gossip of the celestial spheres, logged on to the cosmic Twitter.

So, take my advice: don't attempt for a second to argue with these deluded folk. Simply smite them on the head with a copy of Hume's Enquiry - or, better still, his much heftier Treatise of Human Nature. Hardback, naturally.