What does the Wason Selection Task test?
I'm doing a visual memory test. On the table in front of me are twelve green and fourteen red apples, and an empty basket. The lights go out, and the instructor says to me:
"Put all the green apples into the basket". (1)
I try to do what he says. When the lights go on, you, the instructor's assistant, are given a form on which you are to tick whether I've correctly or incorrectly fulfilled the task. You see twelve green and two red apples in the basket. What do you tick?
The problem is that strictly speaking, I have put all the green apples into the basket, so I've correctly fulfilled the task, because this is exactly what was required. On the other hand, the order (1) was clearly meant as
"Put all and only the green apples into the basket" (1')
and I didn't manage to do that.
Most people, I believe, would understand (1) as (1') and tick "incorrect". It would be odd to accuse them of making a logical mistake. Similarly, the 80-something percent that fail the Wason selection task also shouldn't be accused of making a logical mistake.
What I think the Wason selection task really tests is to what extent "if", in certain contexts, conversationally implies "iff". It does not test logical competence.