Knights and Knaves/Headscratchers

• In the "Only Allowed One Question" scenario, what is stopping the Knave from saying "I do not know"?
  • I suppose the rules have to guarantee that the guards understand which door they are specifically made to guard, otherwise the puzzle doesn't work properly, and can not shirk their understanding of the doors. There are two parts of the puzzle, of course - figure the lie-teller from the truth-teller, and then get one of their opinions on the doors' actual state - and you have just one question to do this. So, basically, "I do not know" is blatant disregard to the point of the puzzle.
  • "I do not know" isn't an answer and thus the question would not count. Therefore, the person asking would have the opportunity to ask another question and/or ask the other guard.
    • What about "Neither," then? That's an answer, and also a lie - by the rules of the game, one of the ways is safe, or trapped, or whatever they ask, so saying neither is a blatant falsehood.
      • The lying guard apparently has no creativity at all, hence always answers with the 180° opposite of the truth.
        • The liar still has to give an answer that could be true, since he wants you to believe his lie, but since you already know that both guards know the answer and one is death the other safety, telling you he doesn't or that neither is trapped (or safe) would be an unbelievable lie.
• Who tells you the rules? If it's a guard, why should you believe it? Actually, if it's not a guard, why should you believe it? Given that they're presumably working for whoever is subjecting you to silly logic puzzles in the first place...
  • It obviously differs in each puzzle, but yes, usually one of the guards tell the rules of the game. Otherwise, there is a sign sticking out of the ground, or a third character who will refuse to tell the answer - only the rules. Though simply having the sign or whatever lie would ruin the purpose of the puzzle: for all we know, if there's a lying sign we have to hug each guard in turn and then do twenty seconds of the Macarena.
  • Also note the Yu-Gi-Oh and Samurai Jack examples on the main page, where the puzzle is a lie.
  • Unless the rules are learnt from a sign or someone other than one of the guards, the logic doesn't work.
• Do no one think that Knaves could be Guarding the Right Way?
  • You asking which way you are going, The Knaves will still lie.
• Why don't they just ask them a question to which the answer is obvious, like "is this apple red?" or something like that. whoever says "no" is the liar.
  • Because it's generally that you're only allowed one question, so you need to ask one that'll give you the right answer regardless of which one answers.
    • And because you want to find out which door to go through, not which one is the liar. The truth teller is not necessarily the one in front of the safe door.
  • There also might be a rule added that says it cannot be a question to which the answer is obviously known. I know I saw it at least once.
    • Smullyan asked that version in Satan, Cantor and Infinity. The man in front of you either always tells the truth or always lies. You must discover which in one yes-or-no question, and you must not know the true answer to the question when you ask it. His solution: shuffle a deck of cards, show the man a card, ask "Is this a red card?", then turn it round and look at it after he answers.
    • Actually, in that particular puzzle you have to discover whether the Vizier is a truth-teller or a liar by asking any number of questions. It wasn't a requirement to use one question only, it's just that that was the solution given. Which led this troper to invent the more interesting question: if you have a person who either always tells the truth or always lies, but you don't know which, can you find out which in any number of yes-or-no questions, if you're forbidden to ask any question to which you already know the answer and forbidden to gain information from sources other than the answers to your questions? (Yes, you can, but I won't give the solution here.)
      • Ask him "is the answer to this question 'no'?". If he answers it, he's a liar. If his head explodes, he used to be a truth-teller.
• For a long time I've had a simple solution: distract one of the knights (say, by asking, "What is the meaning of the little ridge on the crest of the shield design on that other knight's shield?" * pointing* "Right...") and then heaving the motherfucker through the door and see if the trap gets him. Of course, if the trap doesn't get him then I may have to fight off two knights, but whether I survive or not I'll still have solved the riddle, won't I? And I can always take advantage of momentum and the element of surprise and dash past him when no trap befalls him. I'm quick. Not such a brain-teaser after all, is it? Lateral thinking is the name of the game, folks.
  • Unless, of course, the danger behind the door is trained or primed not to target the guard, but the clever dick who pushes the guard through the door then runs through it in a moment of over-confidence moments after...
    • except that it can be expected that the guards a) won't fit through the door b) are too heavy for you to push through the door, or c) have been alone in the room so long that they already know every detail of the room and won't need to look to answer the question thus rendering your distraction moot and wasting your only question.
      • or d) are actually part of the door.
      • I always saw the generic version as having a hallway behind each door, with the trap only triggering some ways down the hall. Thus, shoving them through wouldn't trigger it regardless of which one you shoved them through.

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