The door riddle


I think the best question would be : "Which way leads to certain death?"

The truth teller will answer honestly. The liar will point in the opposite direction leading her to the castle. So in either case she is safe.

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[deleted]

So.. say she asks the guy in the left. The guy in the left tells her the door that leads to certain death is the left door.

Then what? You still can't tell who's lying and who isn't.

If the guy in the left is telling the truth then she should go to the right.
If the guy in the left isn't telling the truth then should go to the left.
Well... you're fvcked then.

You have to make the question filter through both goblins because then you know that it will ALWAYS BE A LIE, since the truth teller will tell the other's lie, and the liar will lie about the other's truth.

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You might as well flip a coin since you still don't know which one is telling the truth and which one is lying.

Can't stop the signal.

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No you don't. You just need to pose the right question to the right person.

One guard always lies, one always tells the truth. You'll never know which is which but they allow you to ask one question to one guard. And knowing that you can then work it out.

If you ask either guard which door leads to freedom he will point to one of the two doors. The one that tells the truth will tell you the truth and the one that lies will lie. So no help there. But if you ask the guard what door the other one would choose then you know not to chose that door.

For example, you ask Guard A which door would Guard B say leads to freedom? He will point to one of the doors. Now, if Guard A is a liar then he will never point to the actual door but instead will lie and point to the other one. However if you ask Guard B who only tells the truth he will honestly point to the door that Guard A would choose.

You can then safely choose the door they didn't point to. Or at least that's how it's supposed to go. I don't remember how they phrased it in the movie but I would think it's similar to that.

It reminds me of a similar puzzle. You're a foreigner traveling in foreign lands and in this land are two peoples. One group are the Slobovians who only tell lies and can't be trusted. The other group are the Archons that only tell the truth and can be trusted.

You're paddling along in your canoe and see three people standing on a dock. Not wanting to tie up your canoe where a bunch of Slobivians might steal it you call out, "are you Slobovians or Archons?"

The first one responds but his words are carried away in the wind. You call out again and the second one responds saying, "he says he's an Archon and he is an Archon and so am I".

The third one calls out, "they're lying to you! They're Slobovians but I'm an Archon!"

Who's who?

The answer is simple. The first two are Archons and the third one is a Slobivian. How did we come to that conclusion?

If asked, either group will answer that they're Archons. An Archon will tell the truth and a Slobovian will lie. So regardless of what the first one said we know that the second one repeated and confirmed what the first one said thus he too is an Archon. Had he been a Slobovian he would have said that the first one said he was a Slobovian but he is an Archon.

As we know the first two are Archons, the third one is then a Slobovian and it's safe to tie up your canoe there.

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I still can't wrap my brain around this riddle. The nearest I can get to some kind of understanding is the phrasing of the question is the key to getting the true answer. Not asking, what's the right door? Instead asking, Which door would the other guy say is the right door?

Is that at least partway correct? That's as far as I get in understanding. After that I'm totally lost.

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The nearest I can get to some kind of understanding is the phrasing of the question is the key to getting the true answer.

And this is exactly it. It's not that difficult once you think about it.

Instead asking, Which door would the other guy say is the right door?

Right. And then you pick the other door. This question always leads you that way because no matter which door is the door to freedom, the answer to your question when phrased like this will always be the door to certain death.

Let's say Door A leads to certain death and Door B leads to freedom. You turn to Guard A and ask him, "what door would your friend say leads to freedom". It doesn't matter if Guard A is a liar or not, he will always point to the door leading to certain death which in this case is Door A. Think about it. If he's a liar, then what door would have Guard B have told you to take? Guard B would say to take Door B but since Guard A is a liar he lies and points to Door A.

Same goes for if Guard A only tells the truth. If you were to ask Guard B which door leads to freedom, he would lie and again point to Door A. Guard A has told you the truth as to which door the liar would tell you to take. So again you can choose Door B.

Make more sense now?

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I'll try to explain it as easy as possible:

If you ask the liar which door the truthful guard would say leads to the castle, he'd lie and give you the wrong one.

If you ask the truthful guard what door the liar would say leads to the castle, he'd truthfully tell you what the liar would say...which is a lie.

So no matter what guard you ask (liar or truthful) they'd both give you the lie by default IF you ask them what the other one would say.

Hope this makes sense.

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lol. It's been almost 30 years and I still don't understand this riddle.

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Yes if you ask them both what door would the other guy say is safe.
The truth teller knows the lier will pick the unsafe door(He points to the unsafe door). The lier knows the truth sayer will point to the safe door so instead (he will point to the unsafe door cause he's a liar). Now both guards are pointing to the safe door. In the case of the laberinth she was only allowed to ask one guard but the out come would be the same. They will point to the wrong door.

This is the fork in the road puzzle in knights and knaves.

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Ok, i think i head just exploded - bang :)))

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One guard always lies, one always tells the truth.
The thing that seems to be overlooked is that one of the guards told Sara this.

I don't love her.. She kicked me in the face!!

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Good point. That actually makes the entire puzzle impossible.

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Both are liars. Neither door leads out of the labyrinth. If Sarah asked the Blue Guard the same question as she asked the Red Guard in the film, he would have said the same thing. I do not know how to simplify the answer, but pretend you are in the film and you asked the guards the same question. Who would you believe, the liar, or the one who only wants you to think the other is a liar to make it appear that they are the truth teller? I hope this makes sense, sorry if it doesn't.

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[deleted]

That's the easiest way of looking at it, the way Sarah phrases it guarantees that the answer she is given is a lie.

If she asks the guy who is telling the truth what the liar would say, he will repeat the lie. Because that is honestly the answer the liar would give.

If she asks the guy who is lying what the honest door would say, he'd lie and say the opposite.

Either way the answer given is a lie, and she must chose the other door.

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[deleted]

The door she took is the door to the castle. She fell in a hole because it was simply another obstacle, and only ended up in the oubliette because she chose to go down. Had she asked the hands to take her back up, and out of the hole, she would have been able to keep going. There was only one liar, and she had the correct path - they never said that there would be no traps or anything, Sarah did not ask that. Also, the oubliette was not "certain death" because the hands gave her a choice, so she still had a chance to avoid it, and if she had known to step over that part she could have avoided it herself.


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[deleted]

The door she took is the door to the castle. She fell in a hole because it was simply another obstacle, and only ended up in the oubliette because she chose to go down. Had she asked the hands to take her back up, and out of the hole, she would have been able to keep going. T

Exactly!!!! That was what I always thought too!!!!
That Sarah did NOT make the wrong choice, she made the correct one!
Her error was (inexplicably) choosing to go Down instead of Up.

But even in a way, choosing Down was the right way....since Hoggle was already assigned to get her out of there.

If the Oubliette was only meant to be a trap with no end, why did Jareth send Hoggle there to find her? Jareth could have just left Sarah there.
There had to be some way out that Sarah could have found.





I'd say this cloud is Cumulo Nimbus.
Didn't he discover America?
Penfold, shush.

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She wasn't trying to get out of the labyrinth at that time though...

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The best question is to just ask "Okay, what would the other door say if I asked which way to go?"

Reasoning: If the honest door answers, he'll say "Well, the other guy would've lied to you."

If he's the one that lies, then he'll say "Take this way." which clearly is the one you DON'T want to go through.

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Gys, guys. All this assumes that 'one of them always tells the truth and one of them always lies'.
Sarah's mistake was in taking the veracity of that statement for granted. If what the goblin said was true, than he just outed himself as the truthful one. If it wasn't true, she may as well have flipped a coin.

I suppose a smaller-caliber gun would have to fire baby teeth.

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I actually thought that the last time I watched this. If "one of them always tells the truth and one of them always lies" is a true statement then the guard who said it is obviously the one who always tells the truth.

Once upon a time there was a magical place where it never rained. The end.

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That bit does kind of mess it up, slightly. I guess they mean only when they're asked questions, they have a rule of always lying and always telling the truth, but they are still allowed to speak truthfully when explaining the rules (though, it would be even sillier if the truth-teller was the one who explained it). I thought that when I watched it at one point - I think to save explaining this they should have had the lower guards explain the rules - they aren't part of the rules, and don't know the way to the castle, but they would know that the other two either lie or tell the truth.


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That messes it up. Because if the guy who said; "One of us always tells the truth, and the other always lies" is a lie, then there's no point at all to what they're doing. Might as well just guess.

I think the assumption is that, the rules of the game are given honestly by both doors BUT every other statement follows the rules of one is honest and is dishonest.

Really, I think it's just something writer's of the film didn't consider when inserting the scene. And if they had, they'd have perhaps had another character explain the rules of the game, or given her advice as to what to do if she met the doors. It's a fairly minor quibble really. As said, just assume the rules to the game are as seen.

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> It's a fairly minor quibble really.

I do not think so. This is supposed to be a logical puzzle, and the writers messed it up. The way they did it, it has only an apparent resemblance to the well-known puzzle. The (somewhat ridiculous) assumption in the riddle is that the characters indeed behave in that extreme way to *always* lie/tell the truth. That assumption is artificial enough, it does not help to make it murky by quietly assuming additional rules.

The way it is, you can only deduce that both characters do not always tell the truth. Because they both agree on the rules, when the red one starts explaining them. Thus it cannot be that one of them *always* lies and the other one *always* tells the truth. But that it exactly what the blue one than says: Always. And the red one nods to it, which makes it even worse.

So basically she is screwed. Obviously she did not chose the path to certain death though, which was a stroke of luck.

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I just assume that one always tells the truth and one always lies, but with one exception. And that exception is that they both explain the rules to the riddle in an honest fashion.

Anything else is overthinking.

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Yea if thats how the movie played out then it already broke the original knights a knaves riddle.

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Based on the scenario in the film it's impossible for her to find the right answer.

One head on the bottom tells her that one door leads to the castle and one door leads to certain doom. The other head on the bottom tells her that they don't know which one is which, to ask the top heads.

She doesn't know if either of them is lying, so she doesn't even know if either door leads to the castle. She can only ask the top heads about where one door leads, so she can't verify this scenario to be true until after she makes her choice. In the event that she can ask multiple questions, she still won't be able to confirm this. I'll get to that later.

If both doors led to doom, the liar would still tell her one of them led to the castle, so she would get the lie either way from her question and she wouldn't know until it was too late.

Next, one of the top heads tells her that she can only ask one question. The other top head tells her one always tells the truth and one always lies.

If head two is telling the truth, then head one is the liar and she can ask more than one question. In that case she can confirm that by asking another question, but that will only prove the first head is a liar, and not whether the second head is true.

Head two could be lying about one of them telling the truth and they both could be liars. Again there is no way to prove that, other than to make the choice and see which one it was afterwards.

*Here's a ****in' spoiler: Everybody dies.*

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I would just ask an unrelated question of something like, "Am I male?" Of course, then I pick the door of the one that says "Yes."

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[deleted]

presumably, you only get one question

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That wouldn't necessarily work.

There's nothing in the rules of the riddle that suggests that the door who is telling the truth is the door you want to go through.

One door leads to the Goblin kingdom at the heart of the labyrinth, the other leads to certain death. The door who is telling the truth might also be the door that leads to certain death. So asking a question to ascertain which one is telling the truth is pointless.

What Sarah is trying to discover is which door to take, not who is telling the truth.

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