The Wason Test


The Wason TestThis is a puzzle named after its creator.

There are four cards lying on a table in front of you. You know for certain that all the cards have one letter marked on one side, and one number marked on the other. Marked on their upper sides are the following:

A F 3 4

There is a statement which is this: “If a card has a vowel on one side, then it must have an even number on the other side.”

How many cards need you turn over, and which cards, to establish whether the statement is true or false?


Try the same puzzle again, but this time, the puzzle will be phrased differently.

There are four men sitting around a table, drinking in a public house. The local law says that it is illegal to drink alcohol in a pub if under the age of eighteen. You are the pub landlord, and you see that some off-duty police are about to enter your pub. You don’t know the four men round the table, and you are anxious to make certain that none is drinking illegally. The four men you can see are:

1. Drinking gin, age unknown        2. Drinking orange juice, age unknown
3. Pensioner, drink unknown        4. Child, drink unknown
How many of these four people need you question, and which ones, to establish whether the law is being broken?


Wason Test: the answer. This test was devised to see how people’s brains work. The same logic puzzle was given to test subjects, but phrased once as an abstract logic puzzle, and once as a social contract. The result was that people showed themselves to be amazingly bad at solving abstract logic puzzles, but very good indeed at solving social problems.

When phrased as an abstract puzzle, the answer is to look at the other side of the vowel card, to make sure that it does not have an odd number on the other side, and at the other side of the odd numbered card, to make sure that it doesn’t have a vowel on the other side. The most common wrong answer is to look at the other sides of two cards: the vowel, and the even number. Turning over the even number card tells us nothing, however. The rule states that a card with a vowel on it must have an even number on the other side, but this does not mean that an even number must have a vowel on the other side. It could be that consonant cards can also have even numbers on the other side of them.

Phrased as a social situation, the problem seems much clearer. The law says that alcohol drinkers must be eighteen or over. So you have to see how old the man drinking gin is, and you must make sure that the child is not drinking alcohol. You do not have to ask the pensioner what he is drinking, because he could drink anything he likes. The law does not say that people over eighteen MUST drink alcohol, just as the abstract statement did not say that an even numbered card MUST have a vowel on the other side.

If you got it right as a social contract, and wrong as an abstract puzzle, then you are normal, and have the sort of human brain which is geared to solving social problems, rather than abstract logic puzzles. Our prehistoric ancestors benefited a lot from being able to spot someone breaking the tribe’s laws, and very little from being able to solve daft pointless puzzles.

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