Page "Wason selection task" Paragraph 6

The correct response was to turn the cards showing 8 and brown, but no other card.

Remember how the proposition was stated: " If the card shows an even number on one face, then its opposite face is red.

" Only a card which has an even number on one face and which is not red on the other face can invalidate this rule.

If we turn over the card labeled " 3 " and find that it is red, this does not invalidate the rule.

Likewise, if we turn over the red card and find that it has the label " 3 ", this also does not break the rule.

On the other hand, if the brown card has the label " 4 ", this invalidates the rule: it has an even number, but is not red.

The interpretation of " if " here is that of the material conditional in classical logic.