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  • Published: 31 October 2017
  • ISBN: 9780141983042
  • Imprint: Penguin Press
  • Format: Paperback
  • Pages: 368
  • RRP: $24.99

The Undoing Project

A Friendship that Changed the World


Danny and Amos had been at the University of Michigan at the same time for six months, but their paths seldom crossed; their minds, never. Danny had been in one build­ing, studying people’s pupils, and Amos had been in another, devis­ing mathematical approaches to similarity, measurement, and decision making.

“We had not had much to do with each other,” said Danny. The dozen or so graduate students in Danny’s seminar at Hebrew University were all surprised when, in the spring of 1969, Amos turned up. Danny never had guests: The seminar was his show. Amos was about as far removed from the real-world problems in Applications of Psychology as a psychologist could be. Plus, the two men didn’t seem to mix. “It was the graduate students’ percep­tion that Danny and Amos had some sort of rivalry,” said one of the students in the seminar. “They were clearly the stars of the depart­ment who somehow or other hadn’t gotten in sync.”

Before he left for North Carolina, Amnon Rapoport had felt that he and Amos disturbed Danny in some way that was hard to pin down. “We thought he was afraid of us or something,” said Amnon. “Suspicious of us.” For his part, Danny said he’d simply been curious about Amos Tversky. “I think I wanted a chance to know him better,” he said.

Danny invited Amos to come to his seminar to talk about whatever he wanted to talk about. He was a little surprised that Amos didn’t talk about his own work—but then Amos’s work was so abstract and theoretical that he probably decided it had no place in the seminar. Those who stopped to think about it found it odd that Amos’s work betrayed so little interest in the real world, when Amos was so intimately and endlessly engaged with that world, and how, conversely, Danny’s work was consumed by real-world problems, even as he kept other people at a distance.

Amos was now what people referred to, a bit confusingly, as a “mathematical psychologist.” Nonmathematical psychologists, like Danny, quietly viewed much of mathematical psychology as a series of pointless exercises conducted by people who were using their abil­ity to do math as camou?age for how little of psychological interest they had to say. Mathematical psychologists, for their part, tended to view nonmathematical psychologists as simply too stupid to understand the importance of what they were saying. Amos was then at work with a team of mathematically gifted American aca­demics on what would become a three-volume, molasses-dense, axiom-?lled textbook called Foundations of Measurement—more than a thousand pages of arguments and proofs of how to mea­sure stuff. On the one hand, it was a wildly impressive display of pure thought; on the other, the whole enterprise had a tree­fell-in-the-woods quality to it. How important could the sound it made be, if no one was able to hear it? 

The Undoing Project Michael Lewis

From the No. 1 bestselling author of The Big Short and Flash Boys, the surprising and profound story of Daniel Kahneman and Amos Tversky: the two men whose ideas changed the world

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