[gweinberg]

The problem is, if you read the rule as "if and only if", then you always have to look at everything, right? But I I think a lot of people who get the answer wrong only apply the only if logic one way. That is, if the rule is "a circle on one side must be yellow on the other", they'll check the yellow side to make sure it has a circle (even though it doesn't have to), but they won't check the square to make sure it isn't yellow. They "understand" that a square on one side and yellow on the other is allowed when they see a square, but not when the see a yellow.