Two people are sitting in a room together: an experimenter and a subject. The experimenter gets up and closes the door, and the room becomes quieter. The subject is likely to believe that the experimenter's purpose in closing the door was to make the room quieter.

This is an example of correspondent inference theory. People tend to infer the motives – and also the disposition – of someone who performs an action based on the effects of his actions, and not on external or situational factors. If you see someone violently hitting someone else, you assume it's because he wanted to – and is a violent person – and not because he's play-acting. If you read about someone getting into a car accident, you assume it's because he's a bad driver and not because he was simply unlucky. And – more importantly for this column – if you read about a terrorist, you assume that terrorism is his ultimate goal.

It's not always this easy, of course. If someone chooses to move to Seattle instead of New York, is it because of the climate, the culture or his career? Edward Jones and Keith Davis, who advanced this theory in the 1960s and 1970s, proposed a theory of "correspondence" to describe the extent to which this effect predominates. When an action has a high correspondence, people tend to infer the motives of the person directly from the action: e.g., hitting someone violently. When the action has a low correspondence, people tend to not to make the assumption: e.g., moving to Seattle.

Like most cognitive biases, correspondent inference theory makes evolutionary sense. In a world of simple actions and base motivations, it's a good rule of thumb that allows a creature to rapidly infer the motivations of another creature. (He's attacking me because he wants to kill me.) Even in sentient and social creatures like humans, it makes a lot of sense most of the time. If you see someone violently hitting someone else, it's reasonable to assume that he's a violent person. Cognitive biases aren’t bad; they’re sensible rules of thumb.

But like all cognitive biases, correspondent inference theory fails sometimes. And one place it fails pretty spectacularly is in our response to terrorism. Because terrorism often results in the horrific deaths of innocents, we mistakenly infer that the horrific deaths of innocents is the primary motivation of the terrorist, and not the means to a different end.

I found this interesting analysis in a paper by Max Abrams in International Security. "Why Terrorism Does Not Work" (.PDF) analyzes the political motivations of 28 terrorist groups: the complete list of "foreign terrorist organizations" designated by the U.S. Department of State since 2001. He lists 42 policy objectives of those groups, and found that they only achieved them 7 percent of the time.

According to the data, terrorism is more likely to work if 1) the terrorists attack military targets more often than civilian ones, and 2) if they have minimalist goals like evicting a foreign power from their country or winning control of a piece of territory, rather than maximalist objectives like establishing a new political system in the country or annihilating another nation. But even so, terrorism is a pretty ineffective means of influencing policy.

There's a lot to quibble about in Abrams' methodology, but he seems to be erring on the side of crediting terrorist groups with success. (Hezbollah's objectives of expelling both peacekeepers and Israel out of Lebanon counts as a success, but so does the "limited success" by the Tamil Tigers of establishing a Tamil state.) Still, he provides good data to support what was until recently common knowledge: Terrorism doesn't work.

This is all interesting stuff, and I recommend that you read the paper for yourself. But to me, the most insightful part is when Abrams uses correspondent inference theory to explain why terrorist groups that primarily attack civilians do not achieve their policy goals, even if they are minimalist. Abrams writes:

The theory posited here is that terrorist groups that target civilians are unable to coerce policy change because terrorism has an extremely high correspondence. Countries believe that their civilian populations are attacked not because the terrorist group is protesting unfavorable external conditions such as territorial occupation or poverty. Rather, target countries infer the short-term consequences of terrorism – the deaths of innocent civilians, mass fear, loss of confidence in the government to offer protection, economic contraction, and the inevitable erosion of civil liberties – (are) the objects of the terrorist groups. In short, target countries view the negative consequences of terrorist attacks on their societies and political systems as evidence that the terrorists want them destroyed. Target countries are understandably skeptical that making concessions will placate terrorist groups believed to be motivated by these maximalist objectives.

In other words, terrorism doesn't work, because it makes people less likely to acquiesce to the terrorists' demands, no matter how limited they might be. The reaction to terrorism has an effect completely opposite to what the terrorists want; people simply don't believe those limited demands are the actual demands.

This theory explains, with a clarity I have never seen before, why so many people make the bizarre claim that al Qaeda terrorism – or Islamic terrorism in general – is "different": that while other terrorist groups might have policy objectives, al Qaeda's primary motivation is to kill us all. This is something we have heard from President Bush again and again – Abrams has a page of examples in the paper – and is a rhetorical staple in the debate. (You can see a lot of it in the comments to this previous essay.)

In fact, Bin Laden's policy objectives have been surprisingly consistent. Abrams lists four; here are six from former CIA analyst Michael Scheuer's book Imperial Hubris:

End U.S. support of Israel Force American troops out of the Middle East, particularly Saudi Arabia End the U.S. occupation of Afghanistan and (subsequently) Iraq End U.S. support of other countries' anti-Muslim policies End U.S. pressure on Arab oil companies to keep prices low End U.S. support for "illegitimate" (i.e. moderate) Arab governments, like Pakistan

Although Bin Laden has complained that Americans have completely misunderstood the reason behind the 9/11 attacks, correspondent inference theory postulates that he's not going to convince people. Terrorism, and 9/11 in particular, has such a high correspondence that people use the effects of the attacks to infer the terrorists' motives. In other words, since Bin Laden caused the death of a couple of thousand people in the 9/11 attacks, people assume that must have been his actual goal, and he's just giving lip service to what he claims are his goals. Even Bin Laden's actual objectives are ignored as people focus on the deaths, the destruction and the economic impact.

Perversely, Bush’s misinterpretation of terrorists' motives actually helps prevent them from achieving their goals.

None of this is meant to either excuse or justify terrorism. In fact, it does the exact opposite, by demonstrating why terrorism doesn't work as a tool of persuasion and policy change. But we’re more effective at fighting terrorism if we understand that it is a means to an end and not an end in itself; it requires us to understand the true motivations of the terrorists and not just their particular tactics. And the more our own cognitive biases cloud that understanding, the more we mischaracterize the threat and make bad security trade-offs.

- - -

Bruce Schneier is the CTO of BT Counterpane and the author of Beyond Fear: Thinking Sensibly About Security in an Uncertain World.

Strong Laws, Smart Tech Can Stop Abusive 'Data Reuse'

Don't Look a Leopard in the Eye, and Other Security Advice

Virginia Tech Lesson: Rare Risks Breed Irrational Responses

Do We Really Need a Security Industry?

How Security Companies Sucker Us With Lemons