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Classic Knights & Knaves

Raymond Smullyan has made a career of writing logic problems. His most famous have to do with a mythical island of Knights and Knaves. Knights always tell the truth, and Knaves always lie.

As you approach the island, you spot three inhabitants on the shore. You call out to them, “Are you Knights or Knaves?” The first says something but you do not hear what he says, so you ask, “What did you say?” The second inhabitant says, “He says he is a Knight, he is and so am I.” The third responds, “He is a Knave, but I am a Knight.” Figure out the true identities of the three individuals.

knight, knight and knave

They are Knight, Knight and Knave. The most basic rule of Knight and Knave island is that no one ever says they are a Knave. Knights always say they are Knights because they tell the truth, Knaves say they are Knights because they always lie. The second must be a Knight, otherwise he would have lied about the firsts response and if so, he must be telling the truth about the first. The third must therefore be a Knave.


Vishal barot

good quiz but easy

Виктория Яцкова

1 - Knight, 2 - Knight, 3 - Knave

Suppose, the 1st one said "I am a Knight", but is a Knave Then the second said truth by saying "He said he is Knight", but lied when said "He is", that is contradiction to the condition "Knights always tell the truth, and Knaves always lie". In this case the first could not be neither the firsts, not the seconds.

So the second inhabitant said truth and is a Knight.

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Submitted by
almost 5 years ago
Difficulty 5.4 ?