History Main / KnightsAndKnaves

* ''DarkSeed 2'' introduces an interesting variation. Two guards, Ik and Uk, guard a door. The player has to tell which one is which, ''and'' if it is day or night. However, there is no sun in their world, and the role of Knight and Knave changes depending if it is day or night. Unfortunately, since the game won't let the player figure it out on his own, he must ask someone else which is the Knight and Knave during day and night.

[[folder: Mythology ]]

'''Red Guard:''' I do not, I tell the truth!

* A sidequest in ''VideoGame/{{Borderlands 2}}'', "[=BFFs=]", has four robbers in a [[MexicanStandoff Truxican Standoff]] over which of them stole the money from a heist they recently pulled off. One of them is telling the truth, and the other three are lying. You can just shoot any of them in the head to complete the quest, but if you properly figure out who took the money, you'll get a better reward. [[spoiler:It's always the one with the bag of cash on his back.]]

*** It gets even worse. The Blue Guard tells Sarah this right after he agrees with the Red Guard that Sarah can only ask one of them. If one of them is always honest and the other always a liar, neither of them should agree on ''anything'' at any time. All bets are indeed off.
** On the other hand, they try to mislead her with a little joke:

** The speaker told Sarah the conditions: "One of us always lies, and one of us always tells the truth." If the conditions were valid, then that particular speaker was the truth-teller. If he was lying, then all bets were off.

-->'''Guard One:''' He lies.\\
'''Guard Two:''' I do not, I tell the truth!

* A Mathnet comic (from ''Series/SquareOneTV'') included in a tie-in magazine issue of ThreeTwoOneContact involved this puzzle. Kate Monday and George Frankly had to find out which of two identical twins were stealing birds from pet stores. One revealed that he always told the truth and his brother always lied - leaving the two detectives to figure out who was the thief. This particular Knights and Knaves puzzle was a variation on the traditional format; no limit on questions allowed was specified. The solution given was to ask the brothers a trick question like "Are you a parrot?" It was reasoned that the brother who always lied would say "yes" and the always truthful brother would say "no".

* In a brainteaser by puzzle writer Dr. Crypton, the protagonist is visiting a one acre desert island, seeking his way to the island's only tourist attraction, a 100-foot tower. He comes to a crossroads, where four roads split off, and there are three natives there. The four possible tribes of natives: always tell the truth, always lie, can answer with truth or lies, or wait for someone else to say something and then say the same thing. And he can ask them only two questions. [[spoiler:The answer is to ignore them completely, as a 100-foot-tall tower on a one acre desert island is impossible to miss.]]

!!Examples

[[folder: Real Life ]]
* An early (as in, from classic Greek times) version of this is the so-called "Epimenides Liar Paradox", in which Epimenides (a Cretan) claims that "all Cretans are liars". Discussed by Raymond Smullyan in ''What is the Name of This Book?'', in which he points out that [[spoiler:it in fact isn't a paradox, but is completely consistent with the assumptions that (1) Epimenides is lying and (2) at least one Cretan tells the truth]].
** Or just that Epimenides meant "all Cretans are liars" as "all Cretans lie a lot", not as "all Cretans lie all the time".
** Also discussed in Creator/TerryPratchett's Literature/{{Discworld}}, where the Epimedines-equivalent gets beaten up by his fellow Cretans before he can explain what he meant when he insulted them.
[[/folder]]

* Spoofed in the Literature/{{Discworld}} novel ''Discworld/LordsAndLadies''. To pass the time on their trip to Lancre, Ponder Stibbons mentions this puzzle to Ridcully and Casanunda. Much to Ponder's annoyance, Casanunda insists that the "logical" solution is to wrestle a weapon from one of the guards and force him at swordpoint to show them which door leads to safety. And inform him that he is going in first, just in case he tries any funny business.

** Also discussed in Creator/TerryPratchett's ''Literature/{{Discworld}}, where the Epimedines-equivalent gets beaten up by his fellow Cretans before he can explain what he meant when he insulted them.

!!Examples:

[[folder: Alternate Reality Games ]]
* ''PerplexCity'' has a version with seven speakers, at least three of whom are knights and three of whom are knaves.
[[/folder]]

[[folder: Anime and Manga ]]

[[folder: Comic Books ]]

[[folder: Fan Fiction]]

[[folder:Film]]
* ''{{Arcade}}'' - though this is a bit of an aversion, since the guards [[spoiler:tell her flat-out which guard is the truth-teller and which is the liar. And then for some reason the heroine asks the liar which way to go.]]
* In Werner Herzog's ''EveryManForHimselfAndGodAgainstAll'', Kaspar Hauser is asked this question by a doctor trying to test his intelligence. The doctor will accept only a complex answer, but Kaspar responds simply (and correctly, since the doctor did not include the proper constraints), "I would ask him if he is a tree-frog."

-->'''Guard One:''' He lies.
-->'''Guard Two:''' I do not, I tell the truth!

* A variant occurs in one of the ''LoneWolf'' gamebooks. A performer brings out two children, masked so as to conceal their genders. One states "I'm a boy" and the other "I'm a girl." The performer confirms that they are indeed a boy and a girl, but at least one of them is lying, leaving Lone Wolf to determine the gender of each without asking any further questions. Of course, given the above information, if one of them is lying, the other must be as well, making this one as straightforward to solve as the classic version.

[[folder: Live Action TV ]]

* Subverted in the MiniSeries ''TheTenthKingdom''. Two doors to safety or death are guarded by a talking frog who offers one question, but claims to always lie (which would make it unsolvable as a logic problem since the rules themselves are in doubt). By now the father of the protagonist Virginia has had it with this kind of puzzle.
--> '''Tony:''' All right, all right. Wait, wait! I have a question! What is the point in having a door that has a horrible death behind it? Huh? (picks up frog)
-->'''Frog:''' Get your hands off me!
-->'''Tony:''' What does that achieve?
-->'''Frog:''' What are you doing?
-->'''Tony:''' I mean, what is the purpose of your life? Just to be a pain?
-->'''Frog:''' Don't touch me there, only my girlfriend touches me there! (Tony throws the frog through one of the doors) WHOA! (Tony slams the door, there's a large explosion and fireball)
-->'''Wolf:''' I guess it's the other one.

* In the series {{Numb3rs}}, the FBI catches a pair of criminals who stole a truck full of aid money. One says that the truck is gone while the other says the truck is still there. Charlie, a mathematican, is able to deduce that the scenario is identical to this one and uses the correct answer, [[spoiler: ask what the other person is going to say. When the answer from both suspects is the same, that the truck is gone, they know it must still be there.]]

[[folder: Tabletop Games ]]

* A similar situation exists in TabletopGame/{{Warhammer 40000}} with Kairos, a Lord of Change, now known as the Fateweaver. He knows everything, but when asked a question, one head gives the correct answer, while his other head give an equally believable lie.
** And, what with him being a demon of Tzeentch, nowhere is it actually stated that the correct answer is given by the same head each time...
* ''DungeonsAndDragons''

[[folder: Video Games ]]
* The town of Zozo in ''VideoGame/FinalFantasyVI'' is part of a Knights and Knaves puzzle where ''everyone'' in town is a Knave, except for one person who doesn't even contribute to the puzzle.
** Its implied that said Knight is not even from said Krave Land to begin with. So every native of the town is indeed a Liar. Actually, there are other people there that don't lie, but none of them are native to it either.
** UnfortunateImplications set in when you consider that the population of Zozo is made up entirely of the lower classes of a nearby town. Presumably they were banished for being pathological liars.

* Played quite straight with three different agents (liar, truth-sayer and alternator) in ''{{Pathologic}}''. Except that you can cheat and use a disguise to figure out which is the liar.

* Discussed in the Canadian kids' show ''RadioActive'', where the students are assigned the problem in class but the proper answer is never figured out.

* A variation of this problem appears as a puzzle in ''EscapeFromMonkeyIsland'', where Guybrush needs to find hidden treasure with the help of two parrots named Huggyn and Kyssin, who are enchanted by voodoo magic to always tell the truth and lie, respectively. The catch with this variation is that you're asking for directions where there are at least three choices at each intersection. Also, the parrots are identical and fly up and off the screen, then come back after answering a question, so you can no longer tell which one tells the truth. [[spoiler:The trick is to intoxicate one of the parrots with caffeine or alcohol, which produces an obvious change in the bird's appearance -- don't worry, it wears off as soon as you finish the puzzle.]]

* The ''WebAnimation/HomestarRunner'' game [[http://www.videlectrix.com/wheresanegg.html Where's An Egg]] is based on this, only with 9 knights or knaves and a limited set of questions you can ask. Oh, and it's in Russian[[hottip:*:The main gameplay is all in pictures, making the game easily playable regardless of the language you speak. The Russian is just the framing device.]]

* This is one of the many [[http://web.archive.org/web/20100914155050/http://powerpuff.wikia.com/wiki/Him_Diddle_Riddle/The_Ms._Keane_Puzzle_Explained puzzles]] presented to ''WesternAnimation/ThePowerpuffGirls'' by Him in the episode "Him Diddle Riddle." Blossom uses the "If I asked the other person..." variant.[[hottip:*:Real Keane (Call here R) tells truth, Fake Keane (Call her F) lies. Blossom asks who the other Ms Keane would say is real. One says "She would say ''she'' was real." The other says "She would say ''I'' was real." Both would obviously claim to be real, but F would say that ''R'' would say that F is the real one]] She then tries to explain the whole thing to Bubbles and Buttercup, whose reactions could be summed as X.X faces. However, if you ''do'' follow the explanation, you find she used the right logic, but picked the wrong one, even though her explanation implies that she knew which one to pick.

[/folder]]

[[folder:Radio]]
* Parodied in the first episode of ''Radio/JohnFinnemoresSouvenirProgramme'' in [[http://www.youtube.com/watch?v=02gfh-h6mTQ this sketch]].

[[folder:Radio]]
* Parodied in the first episode of ''Radio/JohnFinnemoresSouvenirProgramme'' in [[http://www.youtube.com/watch?v=02gfh-h6mTQ this sketch]].
[[/folder]]

* ''DarkSeed 2'' introduces an interesting variation. Two guards, Ick and Uck, guard a door. The player has to tell which one is which, ''and'' if it is day or night. However, there is no sun in their world, and the role of Knight and Knave changes depending if it is day or night. Unfortunately, since the game won't let the player figure it out on his own, he must ask someone else which is the Knight and Knave during day and night.

* ''VideoGame/SonicTheHedgehog2006'' got really ''stupid'' with this one. The Soleanna police force, intent on giving Sonic the runaround, have informed him that to progress beyond this point of the game he must ascertain which of them is the man authorized to open the door preventing him from doing so. Not only that, at least one of the five is going to lie to him. The answer ends up being [[spoiler:that the whole thing is meaningless. The captain is both the liar, and the guy who told you the terms of their little game in the first place, who just so happens to be ''standing right next to the door you need open''. He literally just has to raise his voice to get you through the door; the game was just for his own sick amusement]].

* This is one of the many [[http://powerpuff.wikia.com/wiki/Him_Diddle_Riddle/The_Ms._Keane_Puzzle_Explained puzzles]] presented to ''WesternAnimation/ThePowerpuffGirls'' by Him in the episode "Him Diddle Riddle." Blossom uses the "If I asked the other person..." variant.[[hottip:*:Real Keane (Call here R) tells truth, Fake Keane (Call her F) lies. Blossom asks who the other Ms Keane would say is real. One says "She would say ''she'' was real." The other says "She would say ''I'' was real." Both would obviously claim to be real, but F would say that ''R'' would say that F is the real one]] She then tries to explain the whole thing to Bubbles and Buttercup, whose reactions could be summed as X.X faces. However, if you ''do'' follow the explanation, you find she used the right logic, but picked the wrong one, even though her explanation implies that she knew which one to pick.

* ''JourneyQuest'' does this with Glorion [[spoiler:killing the truth-telling gargoyle, believing the liar, and getting annoyed by the liar contradicting him- finally asking if he wanted to die. The liar, forced by his nature, says yes, and is thrown through the door he has convinced Glorion leads to his death]]... demonstrating its safety.

* Also subverted in an episode of ''WesternAnimation/SamuraiJack''. A two-headed worm claims he'll grant Jack's wish if he can solve this riddle. Jack does, but it turns out ''both'' heads were lying, and one of them swallows him whole.