In the last critical thinking post, I proposed the Wason Selection Task: you’re dealt four cards; red, 3, 8, and brown. The dealer says the rule is if one side of the card is even, the opposite side must be red. Which card(s) must you turn over to prove he’s lying?
Four cards: red, 3, 8, brown; which card(s) must you flip over to prove whether or not (s)he’s lying?
The answer (drumroll)…8 and brown. Like 90% of people, I got it wrong the first time I encountered it. The 3 is completely irrelevant, as it’s an odd number. If the back of the Right is brown, then that falsified the rule. The red is irrelevant, since the rule if the card is even, then the opposite side must be red. That does not mean that a red card cannot have an odd number on the opposite side. The brown must be turned over because if it has an even number, then the claim that if one side is even then the opposite side must be red is falsified.
Here’s another version: four cards with a drink on one side an a beverage on the other, indicating the patrons at a bar. In USA the drinking age is 21. Which cards must you flip over to see whether or not the bartender is breaking the law?: 16, ginger ale, beer, 28 (Answer in next post in the series.)
For the next post in this series I plan on talking about the confirmation bias.