On an April morning in 2001 Christopher Bono, a clean-cut, well-mannered 16-year-old, approached Jackie Larsen in Grand Marais, Minn. His car had broken down, and he needed a ride to meet friends in Thunder Bay. As Larsen talked with him, she came to feel that something was very wrong. "I am a mother, and I have to talk to you like a mother," she said. "I can tell by your manners that you have a nice mother." Bono replied: "I dont know where my mother is." After Bono left, she called the police and suggested they trace his license plates.

On July 1, 2002, a Russian Bashkirian Airlines jets collision-avoidance system instructed its pilot to ascend when a DHL cargo jet approached in the Swiss-controlled airspace over southern Germany. Nearly simultaneously, a Swiss air traffic controller--whose computerized air traffic system was down--offered an instant human judgment: descend. The Russian pilot overrode the software, and the plane began to angle downward.

Larsens intuition was prescient. Police traced the car to Bonos mother, then went to her apartment, where they found her battered body in the bathtub. Bono was charged with first-degree murder. The pilots instinct was also fateful, but tragically so. The two planes collided, killing 71 people.

Such stories make us wonder: When is intuition powerfully helpful? When is it perilous? And what underlies those differences?

"Buried deep within each and every one of us, there is an instinctive, heart-felt awareness that provides--if we allow it to--the most reliable guide," Britain's Prince Charles has said. But bright people who rely on intuition also go astray. "I'm a gut player. I rely on my instincts," President George W. Bush explained to Bob Woodward of the Washington Post regarding his decision to launch the Iraq war. As popular books on "intuitive healing," "intuitive learning," "intuitive managing" and "intuitive trading" urge, should we listen more to our "intuitive voice" and exercise our "intuitive muscle"? Or should we instead recall King Solomons wisdom: "He that trusteth in his own heart is a fool"?

These questions are both deep and practical. They go to the heart of our understanding of the human mind. And the answers could provide a valuable guide in our everyday lives when we must decide whether to follow gut instinct or use evidence-based rationality--such as when interviewing job candidates, investing money and assessing integrity.

As studies over the past decade have confirmed, our brains operate with a vast unconscious mind that even Freud never suspected. Much of our information processing occurs below the radar of our awareness--off stage, out of sight. The extent to which "automatic nonconscious processes pervade all aspects of mental and social life" is a difficult truth for people to accept, notes Yale University psychologist John Bargh. Our consciousness naturally assumes that its own intentions and choices rule our life. But consciousness overrates its control. In reality, we fly through life mostly on autopilot. As Galileo "removed the earth from its privileged position at the center of the universe," so Bargh sees automatic thinking research "removing consciousness from its privileged place." By studying the forces that shape our intuitions, scientists have revealed how this hidden mind feeds not only our insight and creativity but also our implicit prejudices and irrational fears.

What Is Intuition?
Consider the two-track mind revealed by modern cognitive science. In his 2002 Nobel Prize lecture, psychologist Daniel Kahneman noted that Track ("System") 1--our behind-the-scenes, intuitive mind--is fast, automatic, effortless, associative, implicit (not available to introspection) and often emotionally charged. Track 2--our familiar, conscious (explicit) mind--is deliberate, sequential and rational, and it requires effort to employ.

Two phenomena are thought to shape the processing performed by Track 1. Kahneman and his late collaborator Amos Tversky, two Magellans of the mind, proposed one influence. They theorized that humans have evolved mental shortcuts, called heuristics, which enable efficient, snap judgments. "Fast and frugal" heuristics are like perceptual cues that usually work well but can occasionally trigger illusions or misperceptions. We intuitively assume that fuzzy-looking objects are farther away than clear ones, and usually they are. But on a foggy morning that car up ahead may be closer than it looks.

A second influence on our intuitions comes from learned associations, which automatically surface as feelings that guide our judgments. Our life history provides us with a great reservoir of experiences that inform our actions. Thus, if a stranger looks like a person who previously harmed or threatened us, we may--without consciously recalling the earlier experience--react warily. In a 1985 experiment led by psychologist Pawel Lewicki of the University of Tulsa, one group of students was initially split about 5050 in choosing which of two pictured women looked friendlier. Other students, having interacted previously with a warm, sociable experimenter who resembled one of the women, preferred that person by a six-to-one margin [see illustration above]. In a follow-up, the experimenter acted unfriendly toward half the subjects. When these subjects later had to turn in their data to one of two women, they nearly always avoided the one who resembled the unfriendly experimenter.

Intuitions Powers
Our explicit and implicit minds interact. When speaking, for example, we communicate intended meaning with instantly organized strings of words that somehow effortlessly spill out of our mouth. We just know, without knowing how we know, to articulate the word "pad" rather than "bad" or to say "a big, red barn" rather than "a red, big barn." Studies of automatic processing, "subliminal priming," "implicit memory" and instant emotions unveil our intuitive capacities.

Blindsight. A striking example of our two-track mind comes from studies of D.F., a woman who suffered carbon monoxiderelated brain damage that left her unable to recognize objects. Psychologists Melvyn Goodale of the University of Western Ontario and David Milner of Durham University in England found that, functionally, D.F. is only partly blind. Asked to slip a postcard into a vertical or horizontal mail slot, she can intuitively do so without error. Though unable to report the width of a block in front of her, she will grasp it with just the right finger-thumb distance. Thanks to her "sight unseen," she operates as if she has a "zombie within," report Goodale and Milner.

We commonly think of our vision as one system that controls our visually guided actions. Actually, vision is two systems, each with its own centers in the brain. A "visual perception track" enables us, as Goodale and Milner put it, "to create the mental furniture that allows us to think about the world"--that is, to recognize things and plan actions. A "visual action track" guides our moment-to-moment actions. On special occasions, the two can conflict. For example, we consciously perceive a protruding face in the "hollow face illusion" (in which a concave face appears convex). At the same time, our hand, guided by the subconscious, will unhesitatingly reach inside the mask when we are asked to flick off a buglike target on the face [see illustration below].

Reading "thin slices." In their widely publicized studies from the early 1990s, social psychologist Nalini Ambady, then at Harvard University, and psychologist Robert Rosenthal of the University of California, Riverside, have shown that we often form positive or negative impressions of people in a mere "blink" or "thin slice" of time. After subjects observed three two-second video clips of professors teaching, their teacher ratings predicted the actual end-of-the-term ratings by the professors' own students. To get a sense of someones energy and warmth, the researchers found, a mere six seconds will often do.

Even micro slices can be revealing, as Bargh has found in a series of studies conducted from the late 1980s to the present. When he flashed an image of a face or object for just two tenths of a second, people evaluated it instantly. "We're finding that everything is evaluated as good or bad within a quarter of a second," Bargh said in 1998. Thanks to pathways that run from the eye to the brain's rapid-response emotional-control centers--bypassing the thinking part of the brain, the cortex--we often feel before we analyze.

There is presumed biological wisdom to such instant feelings. When our ancestors confronted strangers, those who speedily and accurately discriminated anger, sadness, fear and happiness were more likely to survive and leave descendants. And there appears to be a sliver of truth in the presumption that women may, on average, slightly exceed men at quickly reading others' emotions, reports Judith Hall of Northeastern University, based on an analysis of 125 studies. Shown a silent two-second video of an upset woman, for example, women, more accurately than men, intuit that she is discussing her divorce rather than criticizing someone. Women also have an edge in spotting lies and in discerning whether a man and a woman are genuinely romantic or are a posed, phony couple.

Intuitive expertise. If experience informs our intuition, then as we learn to associate cues with particular feelings, many judgments should become automatic. Driving a car initially requires concentration but with practice becomes second nature; one's hands and feet seem to do it intuitively, while the conscious mind is elsewhere.

Studies of learned professional expertise reveal a similarly acquired automaticity. Rather than wending their way through a decision tree, experienced car mechanics and physicians will often, after a quick look and listen, recognize the problem. After a mere glance at a chessboard, masters (who may have 50,000 patterns stored in memory) can play speedy "blitz chess" with little performance decline. Experienced Japanese chicken sexers use complex pattern recognition to separate up to 1,000 newly hatched female pullets and look-alike male cockerels an hour, with near-perfect accuracy. But all these experts are hard-pressed to explain how they do it. Intuition, said Herbert Simon, another Nobel laureate psychologist, "is nothing more and nothing less than recognition."

Experiments demonstrate that we are all capable of such "nonconscious learning." In Lewicki's research, people have learned to anticipate the computer screen quadrant in which a character will appear next, even before being able to articulate the underlying rule. In recent experiments at the University of Erfurt in Germany, Tilmann Betsch of the University of Heidelberg and his colleagues deluged people with information about the performance of various stock shares over time. Although the participants were unable to recall the return distributions afterward, their intuitive feeling about each stock "revealed a remarkable degree of sensitivity" to its performance. In experiments conducted during the 1980s and 1990s, psychologist Timothy D. Wilson of the University of Virginia learned that gut feelings have also predicted, better than rationally explained preferences, the future of people's romantic relationships and their satisfaction with art posters. Sometimes the heart has its reasons.

University of Amsterdam psychologist Ap Dijksterhuis and his colleagues confirmed the surprising powers of unconscious thought in recent experiments that showed people complex information about potential apartments, roommates or art posters. The researchers invited some participants to state their immediate preference after reading, say, a dozen pieces of information about each of four apartments. A second group, given several minutes to analyze the information consciously, tended to make slightly smarter decisions. But wisest of all, in study after study, was a third group, whose attention was distracted for a time--enabling the subjects' minds to process the complex information unconsciously and to achieve more organized and crystallized judgments, with more satisfying results. Faced with complex decisions involving many factors, the best advice may indeed be to take our time--to "sleep on it"--and to await the intuitive result of our unconscious processing.

Intuitions Perils
So, just by living, we acquire intuitive expertise that enables quick and effortless judgments and actions. Yet psychological science is replete with examples of smart people making predictable and sometimes costly intuitive errors. They occur when our experience has exposed us to an atypical sample or when a quick and dirty heuristic leads us astray. After watching a basketball team overwhelm weak opponents, we may--thinking the team invincible--be stunned when it is overwhelmed by a strong opponent. Or, make your own snap judgment with this quick quiz: In English words, does the letter k appear more often as the first or third letter? For most people, words beginning with k are more immediately available in memory. Thus, using the "availability heuristic," they assume that k occurs more frequently in the first position. Actually, k appears two to three times more often in the third position.

Intuitive prejudice. After actor Mel Gibson's drunken anti-Semitic tirade during a traffic arrest, after comedian Michael Richards's vile racial response to a black heckler, and after New York City police officers in two incidents killed unarmed black residents with hailstorms of bullets, each perpetrator reassured us that he was not racist. At the conscious, explicit attitude level, they may well be right. But their (and our) unconscious, implicit attitudes--which typically manifest wariness toward those unfamiliar to us or those who resemble people with whom we have negative past associations--may not agree. And so it is that people may exhibit a primitive, automatic dislike or fear of people for whom they express sincere respect and appreciation. And whereas our explicit attitudes may predict our deliberate, intentional actions, our slower-to-change implicit attitudes may erupt in our spontaneous feelings and outbursts.

Various experiments have briefly flashed words or faces that "prime" (automatically activate) stereotypes for some racial, gender or age group. Project Implicit, a collaboration among researchers at Harvard, the University of Virginia and the University of Washington, probes the results. Without the participants' awareness, their activated stereotypes often bias their behavior. When primed with a black rather than white face, people may react with more hostility to an experimenter's annoying request. And they more often think of guns: they more quickly recognize a gun or mistake tools, such as a wrench, for a gun. Even the most seemingly tolerant, egalitarian white people will take longer to identify pleasant words (such as "peace" and "paradise") as "good" when associated with black rather than white faces. Moreover, the more strongly people exhibit such implicit prejudice, the readier they are to perceive anger in black faces.

If aware of a gap between how we should feel and how we intuitively do feel, self-conscious people may try to inhibit their automatic responses. Overcoming what prejudice researcher Patricia G. Devine of the University of Wisconsin-Madison calls "the prejudice habit" is not easy. If we find ourselves reacting with knee-jerk presumptions or feelings, we should not despair, she advises; that is not unusual. It is what we do with that awareness that matters. Do we let those feelings hijack our behavior? Or do we compensate by monitoring and correcting our behavior?

Intuitive fears. This much is beyond doubt: we often fear the wrong things. With images of 9/11 indelibly in mind, many people experienced heightened anxiety about flying. But our fears were misaligned with the facts. The National Safety Council reports that from 2001 to 2003 Americans were, mile for mile, 37 times more likely to die in a passenger vehicle than on a commercial flight. For the majority of air travelers, the most dangerous parts of the journey are the drives to and from the airport.

In a late 2001 essay I calculated that if Americans flew 20 percent less frequently and instead drove half those unflown miles, about 800 more people would die in traffic accidents during the next year. In a follow-up article, psychologist Gerd Gigerenzer of the Max Planck Institute for Human Development in Berlin confirmed that the last three months of 2001 indeed produced an excess 353 American traffic fatalities. From their graves, the 9/11 terrorists were still killing us.

And they continued to instill fear. "We're striking terrorists abroad so we do not have to face them here at home," Bush said on a visit to Holland, Mich., my picturesque Midwestern town. "Today's terrorists can strike at any place, at any time and with virtually any weapon," echoed Homeland Security.

We hear. In a 2006 Gallup poll 45 percent of Americans said they were "very" or "somewhat" worried that they or a family member would become a terrorist victim. Nevertheless, the odds that you or I will be victimized by the next terrorist incident are infinitesimal. Even in 2001, the year more than 2,900 perished during the attacks on the World Trade Center and the Pentagon, the average American was 10 times more likely to die in a car accident and 100 times more likely to die a slow smoking-related death.

Why do we so often fear the wrong things? Why do so many smokers (whose habits shorten their lives, on average, by about five years) worry before flying (which, averaged across people, shortens life by one day)? Why do we fear violent crime more than obesity and clogged arteries? Why have most women feared breast cancer more than heart disease, which is more lethal [see illustration on opposite page]? Why do we fear tragic but isolated terrorist acts more than the futures omnipresent weapon of mass destruction: global climate change? In a nutshell, why do we fret about remote possibilities while ignoring higher probabilities?

Psychological science has identified four factors that feed our risk intuitions:

  • We fear what our ancestral history has prepared us to fear. With our old brain living in a new world, we are disposed to fear confinement and heights, snakes and spiders, and humans outside our tribe.
  • We fear what we cannot control. Behind the wheel of our car, but not in airplane seat 17B, we feel control.
  • We fear what is immediate. Smoking's lethality and the threats of rising seas and extreme weather are in the distant future. The airplane take-off is now.
  • We fear threats readily available in memory. If a surface-to-air missile brings down a single American airliner, the result--thanks to the availability heuristic--will be traumatic for the airline industry. Given the difficulty in grasping the infinitesimal odds of its being (among 11 million annual airline flights) the plane that we are on, probabilities will not persuade us. Intuitive fears will hijack the rational mind.

For these reasons, we fear too little those things that claim lives undramatically (smoking quietly kills 400,000 Americans annually) and too much those things that kill in spectacular bunches. By checking our intuitive fears against the facts, with mindfulness of the realities of how humans die, we can prepare for tomorrow's biggest dangers and deprive terrorists of their biggest weapon: exaggerated fear.

In experiments presented at the 2007 American Association for the Advancement of Science meeting, cognitive psychologist Paul Slovic of the University of Oregon observed a parallel tendency to feel proportionately little concern for the many victims of genocide and greater moral concern for dramatically portrayed individual victims. In collaboration with behavioral psychologists Deborah Small of the University of Pennsylvania and George Loewenstein of Carnegie Mellon University, Slovic also found that people were more willing to contribute money to support a single starving African child than to support many such children. Moreover, donations declined sharply when the childs image was accompanied by a statistical summary of the millions of needy children like her in other African countries. "The numbers appeared to interfere with peoples feelings of compassion toward the young victim," Slovic noted. Although it may be true that "the mark of a civilized human is the capacity to read a column of numbers and weep" (as Bertrand Russell allegedly said), the logical Track 2 mind is overridden by the feeling-based Track 1 mind. Mother Teresa spoke for most people: "If I look at the mass, I will never act. If I look at the one, I will."

So, intuition--fast, automatic, unreasoned thought and feeling--harvests our experience and guides our lives. Intuition is powerful, often wise, but sometimes perilous, and especially so when we overfeel and underthink. Today's cognitive science enhances our appreciation for intuition but also reminds us to check it against reality. Smart, critical thinking often begins as we listen to the creative whispers of our vast unseen mind and builds as we evaluate evidence, test conclusions and plan for the future.