Knight, knave and spy

A mysterious island with knights who always tell the truth, knaves who always lie, and spies who can be honest or dishonest at will.

On the island of knights and knaves and spies, you are approached by three men. One wears blue, one wears red, and one wears green. You know that one is a knight, one is a knave, and one is a spy.

The man in blue says, “I am not a spy.”

The man in red says, “I am a knave.”

The man in green says, “If you asked me, I would say that the man in red is the spy.”

What are the true identities of these three men?

Hint:

If the man in red is in fact the spy, could the man in green be a knight? What about a knave?

The solution provided by Popular Mechanics will be given after a few people have tried or around 9 p.m., somewhere there.

2 comments for “Knight, knave and spy

  1. Mark in Mayenne
    May 18, 2020 at 17:56

    Red knave, red would be telling the truth -contradiction.
    Red knight, red would be lying, contradiction.
    Red must be spy.
    Red is spy and lying.
    Blue is knight and telling the truth.
    Green is knave and is lying about what he would say if asked.

    • May 18, 2020 at 19:18

      Oh well done sir!

      The solution given by Popular Mechanics:

      The man in red says, “I am a knave,” and we immediately know this cannot be true. If he were a knave, he would not tell you, and if the statement were true, he could not be a knave. He also cannot be a knight, because he would not lie about being a knave. So the man in red must be the spy.

      The man in blue says, “I am not the spy.” We have already determined that the man in red is the spy, so this is a truthful statement, making the man in blue the knight.

      Which leaves the man in green as the knave. He says, “If you asked me, I would say that the man in red is the spy.” Even though the man in red is the spy, this statement is a lie. If you asked the knave, he would lie and say the man in red is not the spy.

      So the man in blue is the knight, the man in red is the spy, and the man in green is the knave. We will be encountering more knights and knaves and spies, although they will not be so forthcoming with information next week, so make sure to come back for a challenge!

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