Imagine a table with four cards on it, marked ‘A’, ‘B’, ‘2’ and ‘3’. Each card has a letter on one side, and a number on the other. Your task is to determine whether all cards with a vowel on one side have an even number on the other. Which two cards would you turn over? Everybody chooses the ‘A’ card, obviously, but like many people—unless you really forced yourself to think hard about it—you would probably choose to turn over the ‘2’ card as well. That’s because these are the cards which would produce information consistent with the hypothesis you are supposed to be testing. But in fact, the
...more
