Peter Cathcart Wason (* 22 April 1924 in Bath, England; † 17 April 2003 in Wallingford, England) was an English thought psychologist.

He was one of the leading researchers in experimental thought psychology. With his three paradigmatic experiments, the 2-4-6 task, the selection task and the THOG task, he set in motion a worldwide research activity that continues to this day.

His life
Wason comes from a progressive liberal, politically active family. His great-grandfather Peter Rigby Wason and his great-uncle Cathcart Wason were both members of the House of Commons.

After the war, which he spent as a liaison officer in Normandy, he initially went to New College (Oxford) to study English. After a short period as a lecturer at Aberdeen University, he decided to study psychology at University College London in 1950, where he remained for more than 30 years.

Chess

Peter Wason was an International Master in correspondence chess. He was married twice and left two daughters.

Work
Wason was one of the first to use experimental means to investigate the systematic errors made in thinking.

2-4-6 task
The experimenter has devised a rule that produces certain triples of numbers (for example: "any three numbers in ascending order"). He names one of these triples, e.g. 2-4-6, to the test person. Their task is to find out the imaginary rule by trial and error. To do this, they have to name triples of numbers to the experimenter, who then answers with "Yes, this triple corresponds to my rule" or "No, this triple does not correspond to my rule". The test subject is therefore reliant on guesswork and will therefore formulate hypotheses (e.g. "even numbers") and then test them. It has now been shown that the majority of test subjects favour a positive test strategy. This means that they often name triples such as "8-10-12" and so on and always get a "yes" without getting any closer to the solution. In this case, a falsifying test strategy would make more sense, as the obvious hypothesis ("even numbers in ascending order") is narrower than the actual rule.[2] A test strategy that falsifies one's own hypothesis ("even numbers in ascending order") could include: 1) "24-22-04" (falsification "ascending order") and 2) "1-3-7" (falsification "only even numbers"). In the case of "No" for 1) and "Yes" for 2), the probability that the rule is "any three numbers in ascending order" is high.

The suitability of the 2-4-6 task for demonstrating the use of positive test strategies by participants as a result of confirmation bias is highly controversial in the specialist literature. In studies, Ryan D. Tweney, for example, gave separate groups of participants the additional information to the task that they should pursue a confirming or disconfirming test strategy. Both groups had the same success rate in determining the rule. It was concluded that there is no correlation between the success rate of the test and the use of an exclusively positive test strategy[3].

A significant reduction in the number of attempts to determine the correct rule and an increase in the overall success rate when solving the test was achieved by modifying the original test to a categorisation task after introducing the "DAX" and "MED" rules. DAX is the original rule, while MED includes all complementary rules, i.e. those not covered by DAX. However, the participants were unaware of this complementarity and the response consisted only of the answer: belongs to "DAX" or belongs to "MED".

The participants responded with a higher variability of tested number triples compared to the original test, which only contains a single rule as a solution target. The result emphasises the relevance of complementary approaches to solving tasks where an exclusively positive or negative test strategy is less successful,

Selection task
There are four cards in front of the respondent. They show E, K, 4, 7. Each card has a letter on one side and a number on the other. The experimenter says: "If there is a vowel on one side of the card, then there is an even number on the other side." Which cards does the test person have to turn over to check the rule?

Almost all test subjects correctly check the "E" card (modus ponens), many additionally (incorrectly) check the "4" card, hardly anyone (which would be correct) checks the "7" card (modus tollens).

Later, other researchers have shown that the correct choice is made much more frequently when the content is realistic, i.e. less abstract, and/or deontic ("If you want to drink alcohol, you must be at least 18 years old").

THOG task
THOG task

There are four cards in front of the respondent. They show

a black square
a white square
a black circle
a white circle
The experimenter says: "I have chosen a colour (black or white) and a shape (square or circle). A card that has exactly one of these characteristics, but not both, is a THOG. The black square is a THOG. What can you say about the other three cards (is a THOG / is not a THOG / cannot be decided)?"

As with all of Wason's logic questions, it is essential that the experimenter presents the question as precisely and conclusively as possible in the THOG task, as the difficulty of this task arises from the fact that a lot of information has to be considered simultaneously, which places a heavy burden on the working memory.[9] This can be seen from the fact that many test subjects, even if the question was asked precisely, say that the white circle is not a THOG, as it has none of the properties of the black square. No statement could be made about the black circle and the white square. However, this is not correct if we consider all the information given.

The correct solution would be as follows:

The experimenter may have chosen one of these 4 pairs of properties:

black and square
black and circular
white and square
white and circular

We know from the experimenter that the black square is a THOG because it has exactly one of the selected properties. The property that makes it a THOG is therefore either black or square - but not both. The experimenter cannot have chosen 1. black and square, otherwise the black square would not be a THOG. Nor can he have chosen 4. white and circular, as otherwise the black square would have none of the selected properties and would therefore not be a THOG. This means that the experimenter has either chosen 2. black and circular or 3. white and square. In these two pairs, the white circle would in any case be a THOG, as it is either circular as in 2 (but not also black) or white as in 3 (but not also square). The white square and the black circle can therefore not be THOGs, as they would either have both or neither of the properties from pairs 2. and 3.

The solution is therefore: The white circle is a THOG, the other two cards are not THOGs.

Publications
with Philip Johnson-Laird: Thinking and Reasoning. Penguin Books, Harmondsworth 1968
with Philip Johnson-Laird: Psychology of Reasoning: Structure and Content. 1972; paperback: Harvard University Press, 1990, ISBN 0674721276
with Philip Johnson-Laird: Thinking: Readings in Cognitive Science. Cambridge University Press, 1977, ISBN 0521217563
with William Hartston: The Psychology of Chess. Facts on File, 1983, ISBN 0871962268
Literature
Stephen Newstead & Jonathan St. B. T. Evans (eds.): Essays In Honour Of Peter Wason. Psychology Press, 1995, ISBN 978-0-86377-358-7
Weblinks
Obituary in the Daily Telegraph, 21 April 2003
Obituary by Jonathan St B. T. Evans in the Independent, 22 April 2003
Obituary by Philip Johnson-Laird in the Guardian, 25 April 2003
Peter Cathcart Wason on the website of Herbert Huber (with illustrated problems)

Individual references
 Rüdiger F. Pohl (ed.): Cognitive Illusions. A Handbook on Fallacies and Biases in Thinking, Judgement and Memory. Psychology Press, Hove and New York 2004, ISBN 978-1-84169-351-4.
 P. C. Wason: On the failure to eliminate hypotheses in a conceptual task. In: Quarterly Journal of Experimental Psychology. 12, 1960, S. 129-140
 Tweney, Ryan D., et al: Strategies of rule discovery in an inference task. Quarterly Journal of Experimental Psychology, 32, no. 1, 1980, 109-123, doi:10.1080/00335558008248237.
 Maggie Gale, John Ball Linden: Does Positivity Bias Explain Patterns of Performance on Wason's 2-4-6 Task? Proceedings of the Twenty-Fourth Annual Conference of the Cognitive Science Society, 24(24), 2002, 340-344, doi:10.4324/9781315782379-95.
 Christine Hoffmann(2001). Dissertation. Hypothesis Testing - The Influence of Phenomenon Probability and Amount of Information on the Inference Process. Albert-Ludwigs-University of Freiburg i. Br. p. 33

P. C. Wason: Reasoning about a rule. In: Quarterly Journal of Experimental Psychology. 20, 1968, S. 273-281
 If you solve this puzzle, you have brain damage. In: NZZ Folio. 12/07.
 Wason Four Cards Test (page no longer available, found in December 2022. Search in web archives) Info: The link was automatically marked as broken. Please check the link according to the instructions and then remove this note. (PDF; 28 kB). Paper for a seminar by Friedel Bolle, website of the European University Viadrina
 P. C. Wason, P. G. Brooks: THOG: The anatomy of a problem. In: Psychological Research. 41. Jahrgang, Nr. 1, 1979, S. 79-90, doi:10.1007/BF00309425 (english, eurekamag.com [PDF]).

Source: Germain Wikipedia. 

Others: 5 endgame studies composed by Peter Cathcart Wason are selected on Website ARVES