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Grand Illusions

Frank Keil isn’t interested in how much you know. He’s interested in how much you think you know. Here’s the sort of test he’s devised to help him find out:

1. Name the eighth president.

2. Sketch the plot of A Christmas Carol.

3. Tell how to make chocolate chip cookies.

4. Explain the inner mechanism of a flush toilet.

5. But before you begin, answer this: How well will you do on each question?

Chances are, after you’ve measured your expectations against your performance, you’ll find that the flush toilet is where you fell down. Keil is a psychologist who studies the conceptual tool kit people use to make sense of the world, and his signal finding—confirmed in a wide variety of subjects and published in numerous scientific papers (most recently in the August issue of Trends in Cognitive Science)—is that, when it comes to their understanding of how things work, people fool themselves.


Dr. Spock was wrong. You know less than you think you do.

“For facts, narratives, and procedures, we’re actually pretty good at matching our perceptions of our knowledge with reality,” notes Keil. “If we rate our knowledge of, say, the plot of a novel as a 5, that turns out to be an accurate assessment.” But with explanations, there’s a disconnect. “Because you can drive a car or use a computer, you begin to believe you understand how they work,” he says. In other words, knowing that the gas starts flowing when you step on the accelerator gives you the feeling that you also know what’s happening to the gas inside the engine. Keil and his former graduate student Leonid Rozenblit ’03PhD have named this phenomenon “the illusion of explanatory depth.”

Keil has received a special $1.3 million award from the National Institutes of Health for his research on how people understand the world around them. He admits his findings may be disconcerting for those raised on the reassuring words of baby doctor Benjamin Spock ’25, “Relax. You know more than you think you know.” But he believes the tendency is pervasive. He has found it in children and in his graduate students, who thought they knew how zippers and helicopters worked. (He has also found it in his undergraduate students, who thought the grad students only flunked the zipper-helicopter test because of typical grad-student arrogance.)

Keil thinks there are good reasons for our explanatory illusions. They serve as a kind of cerebral shorthand, preventing data overload in our brains. They also give us the mental flexibility to cope with challenging situations. “We’re remarkably good at handling incredible causal complexity,” he explains. “But we’re not detail-crazy mavens who carry annotated blueprints in our heads. Instead, we use folk science—everyday, intuitive, and sketchy concepts that enable us to construct theories on the fly with just as much detail as we need.”

Some of those theories might, for instance, help us raise children. You don’t need a degree in gastroenterology to take care of a newborn; you need to figure out when the baby is hungry. In this sense, Keil says, Dr. Spock was quite right.  the end


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