Wason Selection Task, explained.
The Wason selection task asks which cases must be inspected to test a conditional rule, such as “if a vowel, then an even number.”
Why it happens
A counterexample needs both a vowel and an odd number. A vowel card might hide that odd number; an odd-number card might hide that vowel. An even card cannot contradict the stated rule, whatever letter it hides.
A conditional rule is contradicted by a case satisfying its first condition but failing its second. Looking for confirming cases alone can miss that violation.
Read the result
Select A and 7, then check your selection. Notice why the task asks for potential violations rather than examples that merely agree. The reverse rule, “every even number has a vowel,” was never stated.
A worked example
Auditing an approval policy
A team requires every urgent request to have an approval.
Inspect urgent requests for missing approvals and unapproved requests for urgency.
Ordinary approved requests can confirm compliance without detecting the cases that would break the rule.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
Cards A, K, 4 and 7 each have a letter on one side and a number on the other. The sufficient inspection set is A and 7. Feedback explains each selection without pretending that one response measures reasoning ability.
Where this idea is useful
A practical use
A policy says every urgent request must have approval. Audit urgent requests and unapproved requests, rather than only approved ones.
A common misconception
“Checking only positive examples proves a rule.”
A compatible example does not exclude counterexamples elsewhere. The necessary inspection depends on what could violate the specific rule.
What this explanation leaves out
- Context, interpretation and prior familiarity affect this task. Its answer depends on the explicitly stated one-way rule.
Why does 7 matter when the rule mentions vowels?
Its unseen side might be a vowel. That would pair the first condition with a violation of the required second condition.
What would count as a concrete counterexample to a rule you currently trust?
Associated thinkers
Further reading
Explore the original research or the teaching reference behind this experiment.