Peter Wason

Creative psychologist who laid the foundations for the modern study of thinking and reasoning

Peter Cathcart Wason, psychologist: born Bath, Somerset 22 April 1924; Reader in Psycholinguistics, University College London 1970-82 (Emeritus); married 1951 Marjorie Salberg (died 1984; two daughters), 1986 Joan Williams (marriage dissolved 1995); died Wallingford, Oxfordshire 17 April 2003.

Peter Wason was one of the most creative and influential British psychologists of the post-war era.

He challenged the orthodox view of his time that people were by nature basically rational and logical, demonstrating, by the ingenious construction of novel experimental tasks, a range of what are now known as "cognitive biases". In so doing, he laid the foundations for the modern study of thinking and reasoning, which has become a major international research field. In contrast with most fields of cognitive psychology, the study of this topic is not dominated by American researchers. It is part of Wason's legacy that, to this day, British and European researchers take the lead in the study of human reasoning.

Wason was born in Bath in 1924. After a childhood – by his own account – of "failing school exams with monotonous regularity" and then officer training at Sandhurst, he became a liaison officer in the 8th Independent Armoured Brigade and was injured in Normandy in 1945. He read English at New College, Oxford, where he met his future wife Marjorie Salberg.

In 1950, he decided to start again by reading for a degree in Psychology at University College London. He was to stay at UCL for the rest of his academic career. Following his PhD and a period of work as a research fellow, in 1970 he was appointed to the position of Reader in Psycholinguistics, which he held until his retirement in 1982.

Wason's love of English and English literature had an impact on this work in psychology in several ways, and in the later part of his career he undertook research into the psychology of writing. He was extremely interested in the art of writing, and took great pains to impose the highest standards on his PhD students. He wrote with great clarity and conviction in his own publications, and this is one of the major causes of his influence. However, he could be as hard on himself as on his students. On one occasion he wrote several drafts of an entire book before abandoning it, as he was not satisfied with the final product. His other great passion was chess, which he played only by correspondence – but to a very high standard – eventually achieving the standing of International Master in this form of play.

Wason published most of his psychological work over a 25-year period from the late 1950s up to the early 1980s. Of these publications, probably the most influential was the book Psychology of Reasoning: structure and content (1972; co- authored by P.N. Johnson-Laird). This book was focused almost entirely on the work of Wason and his collaborators at UCL over the previous 15 years – but then that was mostly what the psychology of reasoning consisted of at that time. This work developed several new tasks and paradigms for the study of reasoning that are heavily used to this day, as well as founding a British tradition in the study of cognitive biases. In this context, the term "bias" refers to the tendency of people to err in systematic ways relative to a logical analysis of the problems they are set.

Wason's work was influenced by two academic giants of his period, the philosopher Karl Popper and the great Swiss psychologist Jean Piaget. Popper had devised a highly influential philosophy of science that founded the doctrine of falsificationism. For centuries, philosophers had battled with the "problem of induction", which is that no amount of confirmatory observations can prove the truth of a general claim, such as a scientific law. Popper proposed that the object of science was not to confirm theories, but rather to falsify them, a process which is logically sound. Good theories would survive this effort and endure.

Wason took Popper's analysis to be the correct foundation for hypothesis testing, which he studied psychologically through tasks of his own devising. Contrary to Popper's strictures, Wason claimed on the basis of his experiments that people had a strong confirmation bias. In 1968, he wrote,

In the real world . . . the fixated, obses- sional behaviour of some of the subjects would be analogous to that of a person who is thinking in a closed system – a system which defies refutation, e.g. existentialism or the majority of religions. These experiments demonstrate . . . how dogmatic thinking and the refusal to entertain the possibility of alternatives can easily result in error.

Piaget's developmental theory of human intelligence was enormously influential in the 1960s and beyond. Piaget proposed that children develop through a series of well-identified stages, until as adults they finally achieve the ability for formal, abstract thinking and logical reasoning. Wason, whose interest was in adult reasoning, strongly contested this analysis, demonstrating repeated evidence of illogical reasoning and bias in his adult subjects – mostly undergraduate students at UCL. This work was based mostly on the reasoning task that he most famously invented, the four-card selection task, known to the field as the Wason selection task.

Wason described the selection task, first reported in 1966, as "deceptively simple" (and questioned the English of authors unfortunate enough to describe it as "deceptively difficult"). By this he meant that while it looked easy and straightforward, it was in fact very hard. Only about 10 per cent of people get the problem right, and these were later discovered to be those who are very high in general intelligence. Although a problem in logical reasoning, it has been known to defeat professors of philosophy and logic. Writing of the task in 1968, Wason wrote "the selection task reflects [a tendency towards irrationality in argument] to the extent that subjects get it wrong . . . It could be argued that irrationality rather than rationality is the norm."

Not all contemporary scholars would agree with these views today, but Peter Wason's reasoning problems live on. In particular, many hundreds of psychological experiments have been and continue to be published in which the Wason selection task is used to inform our understanding of human thinking.

Jonathan StB.T. Evans