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).
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
|