The psychologist Daniel Kahneman, who has died aged 90, won the 2002 Nobel prize for economics despite describing himself as “mostly cheering … from the sidelines” of the subject. He achieved celebrity status in 2011 with the pop psychology book Thinking, 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 also provoking him to ask the myriad questions about human behaviour that formed the basis of his often counterintuitive theories. His work revealed the extent to which human beings make erroneous 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 had been 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 was 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 manoeuvre invariably did worse the next time, and those he reprimanded for fluffing a skill did better.
Kahneman immediately realised 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 reverting towards 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, founded on incessant conversation, complementary skills, very high standards of evidence and “continuous mirth”, earned them the nickname “psychology’s Lennon and McCartney”. Between them they unleashed a torrent of examples to show how our largely unconscious perceptual and emotional predispositions merrily undermine our rational selves.
Kahneman and Tversky showed that if people toss a coin twice and get heads both times, they are far more likely to believe that the next toss will produce tails – even though the probability of heads on every 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 of thumb 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 driver than hope of winning. People asked to bet $20 on the toss of a coin will typically not take the bet unless winning yields $40 or more.
Prospect theory, together with work showing that people make different choices between two equally probable outcomes depending on how the question is framed, took the world of economics by storm during the 80s. The economist Richard Thaler took up their ideas and the collaboration gave birth to the new field of behavioural economics. Up to that point, economists 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 people, the world of economics and the world of psychology had rarely interacted.
Kahneman’s collaboration with Tversky petered out when both researchers moved from Israel to North America: Tversky to Harvard and then Stanford in the US, and Kahneman to the University of British Columbia in Vancouver, Canada (1978-86), followed by the University of California at Berkeley (1986-94). As related in Michael Lewis’s 2016 joint biography of the two men, The Undoing Project, their relationship deteriorated to the point where Kahneman told Tversky they were no longer friends. Only days later, Tversky got in touch to say he had incurable cancer.
He died in 1996, aged 59. Kahneman gave the eulogy at his funeral, and included it along with his autobiographical essay on the Nobel website: Tversky would certainly have shared the prize had he lived.
The book Thinking, Fast and Slow brought to a wide readership Kahneman’s integration of his and Tversky’s results with a model of psychological processing that answered the question of how the human race had managed to survive and thrive despite its susceptibility to irrational biases. The model suggests that we initially assess a situation with a fast, intuitive process based on prior experience that in evolutionary terms is often the key to survival. On top of this is a slow, effortful, conscious process that can, but does not always, correct errors made by the first process.
Kahneman was born in Tel Aviv, while his mother was visiting family there. His parents, Rachel (nee Shenzon) and Efrayim, descended from Lithuanian Jews, lived in Paris, where Efrayim worked as a chemist for a branch of the cosmetics company L’Oréal. When Paris fell to the Nazis in 1940 Efrayim was detained in the transit camp at Drancy, but released after six weeks after his boss intervened. The family went on the run, living for part of the time in a chicken coop. They evaded capture but Daniel’s father died of the consequences 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 worrier. At the same time, his fascination with gossip and questions of behaviour, personality and faith set him up for a career in psychology. In 1946 his mother took him and his sister to live in Palestine, becoming 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 Defence Forces, among other things designing a questionnaire for recruits that would improve the dismal predictions of existing tests as to 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 leave in the US, he switched his research interest to questions related to mental effort and attention, and their connections to emotional arousal.
His decade of collaboration with Tversky on decision-making set him up for his subsequent career in North America. Garlanded with many honours, he spent his later years as emeritus professor at Princeton University, New Jersey, publishing his final book, Noise (with two co-authors, Olivier Sibony and Cass Sunstein) in 2021.
Kahneman’s acute self-awareness included his acknowledgment that he shared all the impediments to rational decision-making that his research had revealed. Late in his life he attempted to tackle the often intemperate exchanges between competing social scientists by developing a method called “adversarial collaboration”. He hoped, he wrote, that “more efficient procedures for the conduct of controversies will be part of my legacy”. Even he, however, a leftwing Israeli who “hated the notion 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, in 1978 he married the British cognitive psychologist Anne Treisman. She died in 2018. He spent the final 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 stepgrandchildren.
• Daniel Kahneman, psychologist, born 5 March 1934; died 27 March 2024
