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Named in honour of Peter Cathcart Wason, who first described the task,[2][3] The Wason selection task (aka Four-card problem) is a logical puzzle which is formally equivalent to the following question:

You are shown a set of four cards placed on a table each of which has a number on one side and a coloured patch on the other side. The visible faces of the cards show 3, 8, red and brown. Which cards should you turn over in order to test the truth of the proposition that if a card shows an even number, then its opposite face shows a primary colour?

A response which identifies a card which need not be inverted, or a response which fails to identify a card which needs to be inverted are both incorrect.

## Solution

The correct response is that the cards showing 8 and brown must be inverted, but no other card. Remember how the question was stated: "If the card shows an even number, Then its opposite face shows a primary colour." If we turn over the card labelled "3" and find that it is red, this does not invalidate the rule. Likewise, if we turn over the red card and find that it has the label "3", this also does not make the rule false. On the other hand, if the brown card has the label "4", this invalidates the rule: It has an even number, and does not have a primary colour.

Experiments have shown that, presented with a Wason task as an uncontextualised logic puzzle, people perform very poorly. Furthermore, even of those who respond correctly, some obtain the correct result by conscious application of the contrapositive rule. By contrast, some (though not all) Wason tasks prove much easier when they are presented in a context of social relations.

Adherents of evolutionary psychology have argued that a simple rule distinguishes Wason tasks which people find easy from those that they find difficult. The suggested rule is that a Wason task proves to be easy if the rule to be tested is one of social exchange (in order to receive benefit X you fulfill condition Y) and the subject is asked to police the rule, but is difficult otherwise. If this classification is accepted, then it supports the contention of evolutionary psychologists that certain features of human psychology may be mechanisms that have evolved, through natural selection, to solve specific problems of social interaction, rather than expressions of general intelligence.

## Explanations of performance on the task

In Wason's study, not even 10% of subjects found the correct solution.[1] This result was replicated in 1993.[2]

Some authors have argued that participants do not read "if... then..." as the material conditional, since the natural language conditional is not the material conditional.[3][4] (See also the paradoxes of the material conditional for more information.) However one interesting feature of the task is how participants react when the classical logic solution is explained:

A psychologist, not very well disposed toward logic, once confessed to me that despite all problems in short-term inferences like the Wason Card Task, there was also the undeniable fact that he had never met an experimental subject who did not understand the logical solution when it was explained to him, and then agreed that it was correct.[5]

This latter comment is also controversial, since it does not explain whether the subjects regarded their previous solution incorrect, or whether they regarded the problem sufficiently vague to have two interpretations.

### Policing social rules

As of 1983, experimenters had identified that success on the Wason selection task was highly content-dependent, but there was no theoretical explanation for which content elicited mostly correct responses and which ones elicited mostly incorrect responses.[6]

Evolutionary psychologists Leda Cosmides and John Tooby (1992) identified that the selection task tends to produce the "correct" response when presented in a context of social relations.[6] For example, if the rule used is "If you are drinking alcohol then you must be over 18", and the cards have an age on one side and beverage on the other, e.g., "16", "drinking beer", "25", "drinking coke", most people have no difficulty in selecting the correct cards ("16" and "beer").[6] In a series of experiments in different contexts, subjects demonstrated consistent superior performance when asked to police a social rule involving a benefit that was only legitimately available to someone who had qualified for that benefit.[6] Cosmides and Tooby argued that experimenters have ruled out alternative explanations, such as that people learn the rules of social exchange through practice and find it easier to apply these familiar rules than less-familiar rules.[6]

According to Cosmides and Tooby, this experimental evidence supports the hypothesis that a Wason task proves to be easier if the rule to be tested is one of social exchange (in order to receive benefit X you need to fulfill condition Y) and the subject is asked to police the rule, but is more difficult otherwise. They argued that such a distinction, if empirically borne out, would support the contention of evolutionary psychologists that human reasoning is governed by context-sensitive mechanisms that have evolved, through natural selection, to solve specific problems of social interaction, rather than context-free, general-purpose mechanisms.[6] In this case, the module is described as a specialized cheater-detection module.[6]

Davies et al. (1995) have argued that Cosmides and Tooby's argument in favor of context-sensitive, domain-specific reasoning mechanisms as opposed to general-purpose reasoning mechanisms is theoretically incoherent and inferentially unjustified.[7] Cosmides and Tooby have adapted the Wason selection task to test for one aspect of propositional logic while ignoring general-purpose reasoning based on syllogistic logic, predicate logic, modal logic, and inductive logic. They assumed that the domain-specific hypothesis was correct without first ruling out the general-purpose hypothesis. Moreover, the experiments intended to show that reasoning is not governed by general-purpose rules either fail to eliminate the general-purpose hypothesis or else actually provide evidence supporting it, which according to Davies and his colleagues suggests that the argument in favor of domain-specific reasoning might be empirically false. In addition to that, Cosmides and Tooby assume that reasoning is either determined exclusively by domain-specific or general-purpose algorithms, a dichotomy that Davies et al. view as misconceived.[7]

## References

1. Wason, P. C. (1977). "Self-contradictions" Thinking: Readings in cognitive science, Cambridge: Cambridge University Press.
2. J.St.B.T. Evans et al. (1993). "Human reasoning: The psychology of deduction." Hove: Lawrence Erlbaum Associates.
3. Oaksford, M. (1994). A rational analysis of the selection task as optimal data selection. Psychological Review 101 (4): 608–631.
4. Stenning, K. (2004). A little logic goes a long way: basing experiment on semantic theory in the cognitive science of conditional reasoning. Cognitive Science 28 (4): 481–530.
5. van Benthem, Johan (2008). Logic and reasoning: do the facts matter?. Studia Logica 88 (1): 67–84.
6. Cosmides, L., Tooby, J. (1992). Cognitive Adaptions for Social Exchange. [1]
7. (1995). Logical reasoning and domain specificity. Biology and Philosophy 10 (1): 1–37.

## Key texts

### Books

1. ^  Wason, P. C. (1966). Reasoning. In B. M. Foss (Ed.), New horizons in psychology. Harmondsworth: Penguin.

### Papers

1. ^  Wason, P. C. and Shapiro, D. (1971) Natural and contrived experience in a reasoning problem. Quarterly Journal of Experimental Psychology, 23: 63-71.