Peter Cathcart Wason

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Peter Cathcart Wason (22 April 1924 – 17 April 2003) was an English cognitive psychologist at University College London who helped found the psychology of reasoning. He explored why people often make logical errors and designed famous tests to reveal these mistakes, such as the Wason selection task, the 2-4-6 problem, and the THOG task. He also coined the term confirmation bias, describing how people tend to seek information that supports their preconceptions, even when it leads to wrong conclusions.

Wason was born in Bath, England. His schooling faced challenges, and during World War II he trained as an officer at Sandhurst and served as a liaison for the 8th Armoured Brigade. Injured, he returned home in 1945. After the war he studied English at Oxford University (began 1948) and later shifted to psychology, becoming a lecturer at the University of Aberdeen. He earned a master’s degree in psychology (1953) at Oxford and a PhD (1956) from University College London, where he remained on the faculty until his retirement in the early 1980s.

In his early work, Wason studied language and how people understand sentences. For example, in experiments with statements like “7 is even” or “9 is not odd,” people tended to judge affirmative statements as true faster, while negative statements were judged false faster. He also found that context affects comprehension: people respond more quickly when a situation makes sense.

Challenging the idea that reasoning is purely logical, Wason argued that people are often biased and rely on simple rules or hunches. His 1960s experiments, especially the 2-4-6 task, showed that people form hypotheses and look mainly for confirming examples rather than testing for disconfirming ones, illustrating confirmation bias. The Wason selection task (1966) revealed that most people struggle to test the right possibilities, again due to confirming their ideas. The THOG task and other studies continued this line of research. In 1979, with Shuli Reich, he described the Wason verbal illusion, showing how people misinterpret certain grammatically complex sentences.

Wason’s approach was hands-on and personal; he often observed experiments himself and even asked participants how they felt about the process, adding a human dimension to his work. His legacy lies in reshaping how we understand human reasoning and the biases that affect it.