Psychologist Daniel Kahneman, who has died aged 90, won the 2002 Nobel Prize in economics despite describing himself as “mostly cheering … from the sidelines” of the subject. He achieved celebrity status in 2011 with the pop psychology book Think, fast and slow, at the age of 77 and after a lifetime of rigorous academic research. Such unpredictable events were typical of his long and eclectic career, while they also provoked him to ask the myriad questions about human behavior that formed the basis of his often counterintuitive theories. His work revealed the extent to which people make incorrect judgments in everyday situations and base decisions on those judgments. Steven Pinker called him “the world’s most influential living psychologist”.
From early in his career, working at the Hebrew University in Jerusalem, Kahneman was interested in obtaining results that could be applied to real-world situations. One of his first insights came when he was trying to persuade flight instructors that reward is more effective than punishment when training people in new skills. A member of his class flatly contradicted him, saying that cadets he praised for a successful maneuver always did worse the next time, and those he reprimanded for figuring out a skill did better.
Kahneman immediately realized that the instructor’s reaction had nothing to do with the second performance – it was simply a case of regression to the mean (the cadets reverted to their average result). “It is part of the human condition,” he later wrote, “that we are statistically punished for rewarding others and rewarded for punishing them.”
During the 1970s, Kahneman did most of his work in collaboration with a younger colleague, Amos Tversky. Their partnership, based on non-stop conversation, complementary skills, very high standards of evidence and “constant cheerfulness”, has earned them the nickname “psychology’s Lennon and McCartney”. Between them, they unleashed a barrage of examples to show how our largely unconscious perceptual and emotional predispositions hilariously subvert our rational selves.
Kahneman and Tversky showed that if people toss a coin twice and get heads both times, they are much more likely to believe that the next toss will produce tails – even though the probability of heads on each toss is exactly 50/50. The same fallacy makes gamblers keep playing after a series of losses – surely the next spin must bring a win? They defined what they called “heuristics of judgment”—rules that systematically bias people in their decision-making. They went on to develop what became known as “prospect theory,” demonstrating that fear of losing was a much more powerful motivator than hope of winning. People asked to bet $20 on a coin toss usually won’t take the bet unless winning yields $40 or more.
Prospect theory, along with work showing that people make different choices between two equally likely outcomes depending on how the question is framed, took the world of economics by storm in the 80s. Economist Richard Thaler took up their ideas and the collaboration gave birth to the new field of behavioral economics. Until that point, economists had worked on the assumption that economic agents made rational decisions based on the utility, defined in statistical terms, of a particular course of action. Despite the obvious fact that such actors are usually human, the world of economics and the world of psychology have rarely interacted.
Kahneman’s collaboration with Tversky disappeared when both researchers moved from Israel to North America: Tversky to Harvard and then Stanford in the USA, and Kahneman to the University of British Columbia in Vancouver, Canada (1978-86), followed by the University of California. at Berkeley (1986-94). As recounted in Michael Lewis’s 2016 joint biography of the two men, The Undo Project, their relationship deteriorated to the point where Kahneman told Tversky they were no longer friends. Just days later, Tversky got in touch to say he had incurable cancer.
He died in 1996, aged 59. Kahneman delivered the eulogy at his funeral and included it with his autobiographical essay on the Nobel website: Tversky would certainly have shared the prize if he had lived.
The book Thinking, Fast and Slow brought Kahneman’s integration of his and Tversky’s results to a wide readership with a model of psychological processing that answered the question of how the human race managed to survive and thrive despite of his susceptibility to irrational prejudices. The model suggests that we initially assess a situation with a quick, intuitive process based on past experience that, in evolutionary terms, is often key to survival. Moreover is a slow, painstaking, conscious process that can correct mistakes made by the first process, but not always.
Kahneman was born in Tel Aviv, while his mother was visiting family there. His parents, Rachel (née Shenzon) and Efrayim, descended from Lithuanian Jews, lived in Paris, where Efrayim worked as a pharmacist for a branch of the cosmetics company L’Oréal. When Paris fell to the Nazis in 1940, Efrayim was held in the transit camp at Drancy, but released after six weeks after his boss intervened. The family fled and lived part of the time in a chicken coop. They evaded capture, but Daniel’s father died of the effects of untreated diabetes in 1944, when Daniel was 10 years old, and only six weeks before the Allied landings on D-Day.
Having spent his early years being hunted, as he put it, like a rabbit, Kahneman described himself as a constant worry. At the same time, his fascination with gossip and questions about behavior, personality and faith set him up for a career in psychology. In 1946 his mother took him and his sister to live in Palestine and became some of the first citizens of the state of Israel. Armed with a degree in psychology from the Hebrew University, he undertook his national service in the Israeli Defense Forces, among other things by designing a questionnaire for recruits that would improve the dismal predictions of existing tests about their potential as soldiers.
After a PhD at Berkeley, Kahneman returned to Jerusalem as a junior lecturer, and began research in visual perception. During two years of sabbatical in the USA, he switched his research interest to questions related to mental effort and attention, and their relationships with emotional arousal.
His decade of collaboration with Tversky on decision-making prepared him for his subsequent career in North America. With many honors, he spent his later years as professor emeritus at Princeton University, New Jersey, and published his final book, Noise (with two co-authors, Olivier Sibony and Cass Sunstein) in 2021.
Kahneman’s acute self-awareness included his recognition that he shared all the obstacles to rational decision-making that his research had revealed. He attempted late in life to tackle the often unseemly exchanges between competing social scientists by developing a method called “adversarial collaboration.” He hoped, he wrote, that “more effective procedures for handling controversies will be part of my legacy”. However, even he was a left-wing Israeli who “hated the idea of occupation”, as he told David Shariatmadari in an article for the Guardian in 2015, could not think of an approach to resolving the Arab-Israeli conflict.
Kahneman married the educational psychologist Irah Kahn when they were students. After their divorce, he married the British cognitive psychologist in 1978 Anne Treisman. She died in 2018. He spent the last years of his life with Tversky’s widow, Barbara. She survives him, along with two children from his first marriage, Michael and Lenore, four stepchildren, Jessica, Deborah, Daniel and Stephen, from his second marriage, three grandchildren and four step-grandchildren.
