Not Who They Say

Logic Level 1

The knight always tells the truth, the knave always lies, and the joker can either lie or tell the truth.

If these 3 people are a knight, a knave, and a joker, then which of the following statements is true?

Geoff is the knight Geoff is the knave Victor is the knave Bob is the joker

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Calvin Lin by Calvin Lin

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3 solutions

Anthony Holm
Oct 21, 2016

Relevant wiki: Truth-Tellers and Liars

Geoff says "I am not the knight." The knight can never say this as it would be a lie, thus he must be telling the truth and because the knave can never do that, Geoff is the joker.
Next Bob says "I am not the joker," which we know is true because Geoff is the joker.
So Bob must be the knight. And by process of elimination, Victor is the knave.

13 Helpful 1 Interesting 1 Brilliant 0 Confused

Good way of identifying the first person! Whenever "only one type of person can make this comment", that provides us with a lot of information to work with.

Calvin Lin Staff - 4 years, 7 months ago
Luke Brace
Oct 23, 2016

Victor has to be the knave, this is because the knave always lies. If he said he wasn't the knight/joker that would be the truth! Simple. This may be incorrect logic but it's 12am sorry :)

2 Helpful 1 Interesting 1 Brilliant 0 Confused

Actually all 3 people can say :I am not a knave".

Calvin Lin Staff - 4 years, 7 months ago

I'm my head there was probably subliminal process of elimination that I didn't take into consideration :)

Luke Brace - 4 years, 7 months ago

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Actually, your logic’s correct!

Diana Bradish - 1 year, 1 month ago
Saya Suka
Apr 26, 2021

In contrast to the statement "I am a Knight" which can be said by anyone, the statement "I am NOT the Knight" can only be spoken by a (truthful) Joker since it would be a lie to the real Knight and a truth to an usurping knave. Since Geoff the Joker already made his debut speech, the statement "I am NOT the Joker" must be a truth to whomever speaking it, thus between a Knight and a knave that's left, this statement is impossible for the latter and a natural truth to the former, therefore Bob is our Knight. After these elimination process of two statements and two people, we now have a knave Victor lying with his statement of "I am NOT the knave".

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