The Wason Selection Task - Logic Puzzle That Defeats Most People

🎴 Select a Scenario

"If a card shows a vowel on one side, then it has an even number on the other side."

If P (vowel) → Q (even)

Which cards MUST you turn over to test if the rule is true or false? Click to select, then submit.

A ✓

K ✓

4 ✓

7 ✓

"If a person is drinking alcohol, they must be over 21."

If P (drinking) → Q (over 21)

You're a bartender. Each card shows a person's drink on one side and age on the other. Which cards MUST you check?

🍺 ✓

🥤 ✓

25 ✓

17 ✓

"If a letter is sealed, it must have a 5¢ stamp."

If P (sealed) → Q (5¢ stamp)

You work at the post office. Each card shows one side of an envelope. Which must you turn over to enforce the rule?

✉️ ✓

📭 ✓

5¢ ✓

4¢ ✓

Result

🧠 Why Is This So Hard?

Card	Could Falsify Rule?	Reasoning
A (Vowel)	✓ MUST CHECK	If back is odd, rule is FALSE
K (Consonant)	No need	Rule says nothing about consonants
4 (Even)	No need	Even + vowel confirms, even + consonant is fine
7 (Odd)	✓ MUST CHECK	If back is vowel, rule is FALSE (modus tollens)

❌ Confirmation Bias

We instinctively look for evidence that CONFIRMS the rule (A and 4). But to TEST a rule, we must look for what could FALSIFY it.

🔬 Modus Tollens

If P→Q, then NOT-Q → NOT-P. If odd (not-Q) has vowel (P), rule fails. Most people don't think to check the "7" card.

🍺 Context Effect

With concrete, familiar rules (drinking age), we ace it! We're evolved for social rule enforcement, not abstract logic.

📊 The Numbers

Abstract: 4% correct. Drinking age: 75% correct. Same logical structure—vastly different performance!

"Subjects overwhelmingly failed to select the card that could potentially falsify the rule. They were seeking confirmation rather than falsification."

— Peter Wason, 1966