Three islanders (X, Y, Z) belong to different tribes: Knights (always tell the truth), Knaves (always lie), and Spies (can tell truth or lie). X says: 'I am a Knave.' Y says: 'X is telling the truth.' Z says: 'I am not a Spy.' There is exactly one member of each tribe. Who is the Spy?
X is the Spy.
A Knight cannot say 'I am a Knave' because it would be a lie. A Knave cannot say 'I am a Knave' because it would be the truth. Therefore, X must be the Spy. (This makes X's statement a lie, so Y's statement is false, making Y the Knave and Z the Knight).
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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