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Freeman Dyson on Daniel Kahneman: How to Dispel Your Illusions

Freeman Dyson reviews Thinking, Fast and Slow

Cognitive illusions are the main theme of his book. A cognitive illusion is a false belief that we intuitively accept as true. The illusion of validity is a false belief in the reliability of our own judgment. The interviewers sincerely believed that they could predict the performance of recruits after talking with them for fifteen minutes. Even after the interviewers had seen the statistical evidence that their belief was an illusion, they still could not help believing it. Kahneman confesses that he himself still experiences the illusion of validity, after fifty years of warning other people against it. He cannot escape the illusion that his own intuitive judgments are trustworthy.

Another theme of Kahneman’s book, proclaimed in the title, is the existence in our brains of two independent sytems for organizing knowledge. Kahneman calls them System One and System Two. System One is amazingly fast, allowing us to recognize faces and understand speech in a fraction of a second. It must have evolved from the ancient little brains that allowed our agile mammalian ancestors to survive in a world of big reptilian predators. Survival in the jungle requires a brain that makes quick decisions based on limited information. Intuition is the name we give to judgments based on the quick action of System One. It makes judgments and takes action without waiting for our conscious awareness to catch up with it. The most remarkable fact about System One is that it has immediate access to a vast store of memories that it uses as a basis for judgment. The memories that are most accessible are those associated with strong emotions, with fear and pain and hatred. The resulting judgments are often wrong, but in the world of the jungle it is safer to be wrong and quick than to be right and slow.

System Two is the slow process of forming judgments based on conscious thinking and critical examination of evidence. It appraises the actions of System One. It gives us a chance to correct mistakes and revise opinions. It probably evolved more recently than System One, after our primate ancestors became arboreal and had the leisure to think things over. An ape in a tree is not so much concerned with predators as with the acquisition and defense of territory. System Two enables a family group to make plans and coordinate activities. After we became human, System Two enabled us to create art and culture.

The question then arises: Why do we not abandon the error-prone System One and let the more reliable System Two rule our lives? Kahneman gives a simple answer to this question: System Two is lazy. To activate System Two requires mental effort. Mental effort is costly in time and also in calories. Precise measurements of blood chemistry show that consumption of glucose increases when System Two is active. Thinking is hard work, and our daily lives are organized so as to economize on thinking. Many of our intellectual tools, such as mathematics and rhetoric and logic, are convenient substitutes for thinking. So long as we are engaged in the routine skills of calculating and talking and writing, we are not thinking, and System One is in charge. We only make the mental effort to activate System Two after we have exhausted the possible alternatives.

System One is much more vulnerable to illusions, but System Two is not immune to them. Kahneman uses the phrase “availability bias” to mean a biased judgment based on a memory that happens to be quickly available. It does not wait to examine a bigger sample of less cogent memories. A striking example of availability bias is the fact that sharks save the lives of swimmers. Careful analysis of deaths in the ocean near San Diego shows that on average, the death of each swimmer killed by a shark saves the lives of ten others. Every time a swimmer is killed, the number of deaths by drowning goes down for a few years and then returns to the normal level. The effect occurs because reports of death by shark attack are remembered more vividly than reports of drownings. System One is strongly biased, paying more prompt attention to sharks than to riptides that occur more frequently and may be equally lethal. In this case, System Two probably shares the same bias. Memories of shark attacks are tied to strong emotions and are therefore more available to both systems.

At the end of his book, Kahneman asks the question: What practical benefit can we derive from an understanding of our irrational mental processes? We know that our judgments are heavily biased by inherited illusions, which helped us to survive in a snake-infested jungle but have nothing to do with logic. We also know that, even when we become aware of the bias and the illusions, the illusions do not disappear. What use is it to know that we are deluded, if the knowledge does not dispel the delusions?

Kahneman answers this question by saying that he hopes to change our behavior by changing our vocabulary. If the names that he invented for various common biases and illusions, “illusion of validity,” “availability bias,” “endowment effect,” and others that I have no space to describe in this review, become part of our everyday vocabulary, then he hopes to see the illusions lose their power to deceive us. If we use these names every day to criticize our friends’ mistaken judgments and to confess our own, then perhaps we will learn to overcome our illusions. Perhaps our children and grandchildren will grow up using the new vocabulary and will automatically correct their congenital biases when making judgments. If this miracle happens, then future generations will owe a big debt to Kahneman for giving them a clearer vision.

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