In 2011, Giuliano Mignini, the prosecutor responsible for making a pig’s breakfast of the Monster of Florence case and damaging, possibly beyond repair, the futures of Raffele Sollecito and Amanda Knox, defended himself against charges that he’s a conspiracy buff this way:

“Why do they call it a conspiracy theory?” he asked. “What does ‘conspiracy theory’ mean? How can you call a conspiracy theory the fact that more than one person did a crime together? Why are they called conspiracy theories? Caesar was killed by 20 senators. Is that a conspiracy theory? It’s normal that people work together. I remember Ruby and Oswald together. Ruby killed Oswald to shut him up. I could see that on TV. Why did he kill him? He was afraid he was going to talk.”

I don’t agree with Mignini on much, but I’ll go this far with him. Conspiracies do happen. We’ve lost at least one and possibly two presidents to assassination conspiracies. 9/11 was certainly a conspiracy involving 19 men with financing from Osama Bin Laden. The Oklahoma City Bombing was mostly Timothy McVeigh’s responsibility, but two of his friends were involved.

The question is how we can distinguish between a reasonable inference of conspiracy and a  conspiracy theory based on paranoid logic. Feeling is not enough. As Kathryn Schulz reminds us,   being wrong feels exactly like being right. So we need some criteria to help us separate sense from nonsense.

1. Has the theorist considered Ockham’s Razor?

Ockham’s razor is a philosophical principle. It’s been stated many ways, but the best known formulation goes like this: if two competing theories explain a phenomenon equally well, the simpler one is more likely to be correct.

Why should this be so? Because if a more complicated theory performs only as well as the simpler one, it is likely the former theory’s complications are superfluous. A more complicated theory should have more explanatory power if it’s to be preferred over the simpler one.

When testing for a conspiracy, it makes sense to try to whittle events down to their simplest terms (without ignoring facts) and work out whether the crime could have been caused by a single agent, or had to have been done by multiple persons acting in concert. In the case of 9/11, it’s clear we can’t hold a single person responsible. The crime involved four nearly simultaneous hijackings, each requiring multiple agents to carry them out. An inference of conspiracy is reasonable and in line with Ockham’s razor.

It should be pointed out here that employing Ockham’s razor does not, on its own, falsify more complicated theories of events. It just encourages us to look first for simpler explanations unless the drift of evidence forces us to embrace more exotic solutions.

2. Does the theorist have any biases against the accused conspirators?

Biases are the bane of clear thinking, and unfortunately, we all have them. Fundamentalist Christians believe that there’s a secular (or sometimes secular/Muslim) plot to destroy Christianity. American right-wingers thought the communists were conspiring to take us over through water fluoridation. In the 19th century, Anti-Masonics were convinced that the secret society of Masons was planning to destroy the American Republic. Anti-Vaxers think that pharmaceutical companies, whose business practices they dislike (and there are sound reasons for disliking them), are conspiring against their children and giving them autism.  Birthers believe President Obama, whom they hate, must have been born in Kenya and that a 46 year conspiracy put him into power. Nazis thought that the Jews, their eternal enemy, had conspired to use both capitalism and communism to crush the Aryan race.

The list of biases we entertain is endless, and it typically starts with hatred and fear of some other, a member of what sociologists call an out-group. The conspiracy minded will transform this person or group of persons into figures of pure malevolence:

The enemy is clearly delineated: he is a perfect model of malice, a kind of amoral superman—sinister, ubiquitous, powerful, cruel, sensual, luxury-loving. Unlike the rest of us, the enemy is not caught in the toils of the vast mechanism of history, himself a victim of his past, his desires, his limitations. He wills, indeed he manufactures, the mechanism of history, or tries to deflect the normal course of history in an evil way. He makes crises, starts runs on banks, causes depressions, manufactures disasters, and then enjoys and profits from the misery he has produced. The paranoid’s interpretation of history is distinctly personal: decisive events are not taken as part of the stream of history, but as the consequences of someone’s will. Very often the enemy is held to possess some especially effective source of power: he controls the press; he has unlimited funds; he has a new secret for influencing the mind (brainwashing); he has a special technique for seduction (the Catholic confessional).

–Richard Hofstadter The Paranoid Style In American Politics

It’s tempting to think of people we dislike this way, to assign them powers we wish we had, and to condemn them for moral failings that allow us to assume a position of righteousness. They are ruthless for evil, giving us permission, if not the duty, to be equally ruthless for good.

Bad results can come from thinking like this, which is why, even when we feel justified in believing the worst about people we dislike, it’s best to pull back and assess whether we’re really looking at them as they are.

3. Does the theory explain every fact in terms of the conspirators’ agency when coincidence explains just as well?

One of the cliches of detective fiction is the detective who, dissatisfied with a neat solution to the case he’s working on says, “I don’t believe in coincidence.” Inevitably, the detective turns out to be right. The coincidence in question always, when examined closely, unravels the criminal’s master scheme.

The thing about coincidences though is that, however unlikely they may seem, given the sheer number of people in the world, even the most unlikely ones will probably have happened to someone, like the guy who won the lottery three times. Because coincidence is much more common than we think it is, we tend to imagine that there’s something underneath every coincidence we encounter, something with intent, like psychic powers or conspiracies.

Here are some 23 coincidences that 9/11 truthers like to imagine add up to conspiracy. I won’t debunk all these, but #2 is a useful example.

2. “A NEW PEARL HARBOR”

The Project for a New American Century (PNAC) was a neo-con think tank stacked with future members of President George W. Bush’s entourage including Dick Cheney, Jeb Bush, Paul Wolfowitz, Donald Rumsfeld, Scooter Libby and Richard Perle.

In September 2000, PNAC published a controversial and aggressive study called “Rebuilding America’s Defenses.” Among very concise outlines on military expansion in the Persian Gulf, the paper deduces “the process of transformation, even if it brings revolutionary change, is likely to be a long one, absent some catastrophic and catalyzing event — like a new Pearl Harbor.”

They say that if you want to find out who started a war, ask: “Who ended up with something in the end?”  Post September 11, the four horseman of PNAC (Cheney, Wolfowitz, Libby and Perle) were the main catalysts for moving into Iraq despite no WMDs. Is it all just a coincidence that the policy they advocated was fulfilled after only a year of power?

Is it all just a coincidence? I’m confident the answer is yes.

It’s one thing to say that Cheney and his buddies took advantage of 9/11 to pursue their favored middle eastern policies. That’s what history’s opportunists do. It’s something else to prove that they orchestrated 9/11 to give themselves this opportunity, and appeals to coincidence are not sufficient proof. Yes, they spoke about a “New Pearl Harbor”, but that’s another coincidence, made sinister only with hindsight. It’s an American habit to refer to events and personages of World War II when selling our foreign policy to others and to ourselves. That’s how every adversary we go to war with is turned into the next Hitler. It’s why people like Cheney always denigrate diplomacy as appeasement. The PNAC didn’t invoke Pearl Harbor as code for their plan to mount a false flag operation. (If they were really planning one, why bother dropping the hint?) It’s because they, like a lot of us, have World War II metaphors on the brain.

4. Does the conspiracy require superhuman powers of coordination, planning, and execution?

The thing about real life conspiracies is that stuff goes wrong, even with the successful ones.

John Wilkes Booth’s conspiracy to kill Lincoln didn’t stop at Lincoln. Two of his minions were supposed to kill Secretary of State William Seward and Vice President Andrew Johnson. Seward, though wounded, survived his assassination attempt, while Johnson’s assassin got drunk and failed to carry out his assignment. And Booth blew his getaway, getting his spur caught in the Presidential box’s bunting as he leaped to the stage, breaking his leg. He was lucky to get out of D.C. alive, but didn’t make it much farther.

That this happens is a great indicator that conspirators are not “perfect models of malice” but ordinary human beings–prisoners, as we are, of a contingent world.

Conspirators in paranoid-land, by contrast, are capable of extraordinary feats. Their workmen can plant all the charges necessary to bring down two huge skyscrapers without anyone noticing them. They can manipulate terrorist organizations to claim responsibility for their actions. They can fake air crashes and hide all the passengers and crew for twelve years without anyone getting wise.

This would require incredible powers of coordination and planning and execution, getting large numbers of people unrelated by profession, personal relationship, or ideological commitment to agree to a scheme because…well, because it’s just too darn good, I guess. What are the odds of anyone successfully assembling such a coordinated group of strangers, getting them all to the right places, and executing the plan without anyone getting wise or any participants defecting? Very, very low.

The same goes for any theory that can only work if one of the participants can control the media, befog minds, appear/disappear without a trace, or summon secret assistants. Unless the theorist has extraordinary evidence to back up such claims, treat them with extreme caution.

5. Does the conspiracy theorist connect many of his dots with speculation or post-hoc rationalization instead of inferences based on evidence?

Everybody speculates. All the time. It’s instinct, honed by millions of years of evolution. Animals that hear a noise in the bushes and leap to the conclusion PREDATOR, run and (probably) live. Animals that pause to judge until all the facts are in may discover the noise was nothing to worry about, but they also may be lunch.

Our brains are terrific at speculating, which not only facilitates our survival, but is also the source of much of our creativity and empathy. It allows us to imagine ourselves in circumstances we’re unlikely to encounter and feel compassion for those we otherwise couldn’t understand. It’s the basis of my chosen art.

But here’s the thing about speculation, or let’s just use its synonym, guessing. It can be right, but it can also be wrong. And wrong guessing has its consequences, as one of my heroes, Kurt Vonnegut, pointed out:

Human beings have had to guess about almost everything for the past million years or so. The leading characters in our history books have been our most enthralling, and sometimes our most terrifying, guessers.

May I name two of them?

Aristotle and Hitler.

One good guesser and one bad one.

Even in that pair, the good guesser, Aristotle, guessed wrong sometimes, while the bad guesser, Hitler, guessed right sometimes. But whoever’s doing it, guessing has a reasonably high error rate. This means that the more guesses that underlie a theory of events, the greater the chances that the theory in question is wrong.

Of course, evidence can turn up which can substantiate a guess, at which point it’s no longer a guess but a legitimate hypothesis. Conspiracy theorists often either skip this step entirely and assume their guess has been confirmed (begging the question), or they seek only evidence confirming their guess while ignoring evidence that falsifies it. The latter often leads the conspiracy theorist to dismiss evidence with strong inferential power in favor of evidence with weak inferential power.

How do they dismiss evidence with strong inferential power, you ask? Simple, though the patented conspiracy theory cleaning action of Post-Hoc Rationalization (trademark pending).

Post-hoc rationalization is best understood as the other end of speculation. Speculation is usually a first response to an event and is instinctive. Post-hoc rationalization, as the “post-hoc” in the name suggests, occurs after obtained evidence concerning an event has been gathered. A post-hoc rationalization is a form of speculation meant to explain away evidence contrary to a belief. Holocaust deniers are masters of this.

Let us examine how the convergence of evidence works to prove the Holocaust, and how deniers select or twist the data to support their claims. We have an account of a survivor who says he heard about the gassing of Jews while he was at Auschwitz. The denier says that survivors exaggerate and that their memories are unsound. Another survivor tells another story different in details but with the core similarity that Jews were gassed at Auschwitz. The denier claims that rumors were floating throughout the camps and many survivors incorporated them in their memories. An SS guard confesses after the war that he actually saw people being gassed and cremated. The denier claims the confessions were forced out of the Nazis by the Allies. But now a member of the Sonderkommando–a Jew who had helped the Nazis move dead bodies from the gas chambers and the crematoria–says he not only heard about it and not only saw it happening, he had actually participated in the process. The denier explains this away by saying that the Sonderkommando accounts make no sense–their figures of numbers of bodies are exaggerated and their dates incorrect. What about the camp commandant, who confessed after the war that he not only heard, saw, and participated in the process but orchestrated it? He was tortured, says the denier. But what about his autobiography, written after his trial, conviction, and sentencing to death, when he had nothing to gain by lying? No one knows why people confess to ridiculous crimes, explains the denier, but they do.

–Michael Shermer Why People Believe Weird Things (215)

This is just the deniers getting warmed up. Shermer goes on to show them explaining away 18 different kinds of evidence, including forensic evidence taken from the camps; photos taken by bombers on their way to attacking the IG Farben plant showing evidence of prisoners being marched toward the crematoria; the minutes of the Wannsee Conference and diary entries from Himmler, speeches by Himmler, Goebbels and Hitler suggesting both homicidal intent and orders to commit genocide; the population statistics suggesting a large number of excess deaths in the populations of European Jews and Roma. Deniers swat away at all them with post-hoc rationalization. It’s a key component of their ideological immune system.

Beware any conspiracy theory that depends on frequent speculation or dismisses contrary evidence by post-hoc rationalization. It may be right, but the overwhelming odds are that it’s wrong.

Conspiracies sometimes do happen. 9/11, the Holocaust, and the Lincoln assassination are just three examples. So it’s a bad idea to dismiss them out of hand. But wrong conspiracy theories can do tremendous damage, to people falsely accused, to institutions, to nations, and to the world. Conspiracy theories sow fear and mistrust, and incite violence. 

I’ll leave where we began, with Amanda Knox’s prosecutor. In his handling of the Kercher murder, and the Monster of Florence case, he’s shown a penchant for leaping to conspiratorial conclusions, in the process making most of the mistakes I’ve listed here. That he’s managed to convince others of his theories doesn’t surprise me–I’ve lived long enough to see humanity fall for a lot of BS–but it does demonstrate just how hard critical thinking really is, and how few of even our most educated neighbors are practiced at it.

I doubt it’s possible to turn Mignini around by pointing out his errors in reasoning. But it is essential to speak to the uncommitted and unaware, and not just to tell them that a conspiracy theory (or any other belief) is bunk, but to show them how they can work these issues out for themselves. By getting people to recognize their own susceptibility to paranoid conspiratorial claims, we might be able to limit the damage that charlatans like Mignini can do.