🔍 Logic & Deduction
Truth-tellers, liars, and careful reasoning
🎯 Process of elimination
Start with the most restrictive clue. Cross out impossibilities until only one answer remains. Don't worry if you get stuck — logic is detective work!
Example:
Amy doesn't have the dog. Ben doesn't have the cat. Amy doesn't have the fish. What does Amy have? Amy can't have dog or fish, so Amy MUST have the cat!
🤥 Truth-tellers and liars
If someone always lies, then the opposite of what they say is true. A tricky part: a liar talking about themselves still lies.
Example: A liar says "I am a truth-teller." That's a lie (they're not a truth-teller). But if a truth-teller says "I am a truth-teller," that's true! Pay close attention to WHO is speaking.
Watch out: "If a liar says 'I am a knave,' can that ever make sense?" Think carefully — what if they say "I'm honest"? It's a lie. What if they say "I'm dishonest"? That would be true, so a liar can't say it. Contradiction!
→ Conditional reasoning
"If A then B" does NOT mean "if B then A." This is one of the biggest tricks in logic!
Example: "All cats are animals" is true. But that does NOT mean "all animals are cats" — that's obviously false! Many other animals exist.
The contrapositive IS equivalent: "If A then B" is the same as "If not B, then not A." All cats are animals = If not an animal, then not a cat. That's logically sound!
🧠 Practice Quiz
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