Remember we have four cards which have the sides telling us:

Side 1:

The brand we put in the fridge.

Side 2:

The number left over.

And we lay out the cards thusly:

So which cards do we turn over to find out if the statement:

If you're out of Schlitz, then you're out of beer.

... is TRUE?

And we again remind everyone:

You can't run out of a brand you didn't have. That is, if you had Bud, you can't run out of Schlitz.

We only want the minimum number of cards and what they are.

Now for the answer.

Remember that the - quote - "correct answer" - unquote - is found what logicians call Material Implication. The corresponding Truth Table is:

And using this Truth Table we can quickly find the answer:

Card 1:

Here we see the THEN part of the statement - "You're out of beer" - is TRUE. And the Truth Table shows us that as long as the THEN part of a Material Implication is TRUE, the whole IF-THEN statement must also be TRUE. We don't need to turn the card over.

Card 2:

Here we had Bud and so we can only be out of Bud. So the statement "You're out of Schlitz" must always be FALSE. As the Truth Table shows us, as long as the IF part of a Material Implication is FALSE, the whole IF-THEN statement is TRUE. So we don't need to turn this card over either.

Card 3:

Here the statement "You're out of beer" is FALSE. And in Material Implication, the whole IF-THEN statement may be TRUE or FALSE depending on what the IF part says. So we have to turn the card over.

Card 4:

On the final card, saying "You're out of Schlitz" - which is the IF part of the Material Implication - can make the entire IF-THEN statment be either TRUE or FALSE depending on what is on the other side of the card. So we have to turn the card over.

So we have to turn over Cards #3 and #4. Just as in our other examples.

But does this support the idea that the Wason Selection Test indicates that the human mind has evolved to recognize deception? Only evolutionary psychologists know for sure.

But of course they may be wrong!

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