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Why is it so hard to test a simple if-then rule?

Four cards show A, D, 4, and 7. Each has a letter on one side and a number on the other. To test ‘if there is a vowel on one side, there is an even number on the other,’ which cards must you turn? Explore why a possible counterexample matters more than another confirming example.

3–7 min

Questions you could explore

  • Why do A and 7 need checking, while seeing an even number does not require a vowel on the other side?
  • How does reversing the if-then rule change which evidence would count against it?

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