## Case 1:

 if a card has a D on one side then it has a 7 on the other if P then Q

 D F 7 5 P not P Q not Q Card #1 Card #2 Card #3 Card #4

Logical answer:

Given the truth table for "if . . . then . . ."

 Q is true Q is false P is true "If P then Q" is true "If P then Q" is false P is false "If P then Q" is true "If P then Q" is true

a proposition of the form If P then Q is falsified if and only if P is true and Q is false.

Since we are looking for falsifying instances -- which are cases of P and not-Q -- we need to check anything that is P (to see if it might also be not-Q), and anything that is not-Q (to see if it might also be P). Things that are not-P and things that are Q are irrelevant.

Therefore, the correct answer, in the Wason trial above, is:
"Card #1 and card #4" -- because this corresponds to the instance of P (card #1) and the instance of not-Q (card #4).

(Of course, in real experiments there are many trials, and the order of the cards is varied).

## Case 2:

 if someone drinks beer then (s)he is 21 or older if P then Q

 beer diet coke 23 years old 19 years old P not P Q not Q Card #1 Card #2 Card #3 Card #4