What is the answer to the "Labyrinth" riddle?

Is there a correct solution to the riddle featured in the Jennifer Connolly/David Bowie film, Labyrinth?
There are two doors, one leads to hell, the other to heaven, and one is guarded by a keeper who always tells the truth and the other is guarded by a keeper who always lies. What question do you ask to find out which door is which*?
In the film Connolly’s logic is wrong and she gets the wrong door.
*that is if there is an actual answer to the riddle.

I could perhaps have been a bit clearer so apologies but hopefully someone will know what i’m on about,

“If I were to ask you which door leads to heaven, how would you respond?”

You ask either one, what door would the other keeper say leads to heaven. If you get the truth teller, he will tell you the truth and that door leads to hell. If you ask the liar he will lie about the door and you get the door to hell. Either way you choose the other door. :wink:

Ask one of the guards, “If I asked you which door leads to heaven, which door would you tell me?”

If the guard tells the truth, he’ll show you the door leading to heaven, of course.

What if the guard is a liar? Well, if you asked him which door leads to heaven, he’d point to the door leading to hell.

But that’s not the question we asked–we asked, “If I asked you which door…” So he’s going to lie about that and point to the door leading to heaven.

So either guard will point out the correct door.

(This may not be the only question that works, of course).

Yes, it’s logic puzzle 101.

Ask guard A the following: “If I asked guard B which was the door to Hell, what would he say?”

If A is the truthteller and B is the liar:
A knows that B would indicate the Heaven door, since B is a liar. A, being a truthteller, correctly reports what B’s choice would be and indicates the Heaven door.

If A is the liar and B is the truthteller:
A knows that B would indicate the Hell door, since B tells the truth. A would then lie about this, and thus A indicates the Heaven door.
In either case, the Heaven door is indicated.

Hmm, if four simulposts fall in the forest, do they make a sound?

Why do you think her answer in the film was wrong?

In fact, Sarah’s logic is correct in Labyrinth. If it hadn’t been, the door would have led to certain death and the movie would have been over. :slight_smile:

But this is quite the elementary logic puzzle. A more complex variant is “God, the Devil, and Bob.” There are three identical people in front of you. One is God, who always tells the truth. One is the Devil, who always lies. One is Bob, whose answers are completely random. Your objective is to determine who is who by asking three yes/no questions.

Why not just ask if it is raining? Or if rhinoceri are purple?

I prefer the way they answered a similar question in 10th Kingdom.

You can’t ask if it’s raining because you only get one question. They don’t say that outright, but that’s usually how the puzzle works.

And I always thought that

she fell down the hole because “things aren’t always as they seem” and she had been tricked (well, LIED to, I guess). She only lived because Hoggle freeing her from the oubliette, and that was unplanned. Maybe I got that from the book.

watches a little further Well, unplanned as far as the guards knew.

If you only get one question, none of the already given answers(questions) necessarily work without further provisions. Though nocturnal tick & Cabbage’s are arguably better.

The reason:

[spoiler] The liar is perfectly free to answer your question in any way, as long as it’s a lie. Thus if you happen to ask the liar what the liar or the other person would say, the liar may answer, “Green apple pig!” (an obvious lie). You now know who’s the liar, but that doesn’t help you pick a door.

Arguing in this way against the question that asks about the doors themselves seems more questionable, since “green apple pig” is really a non-answer to your question, not the same as a lie. The key is to give the respondent only two choices (in Cabbage’s question it’s implicit that only a door can be answered). The stipulation that either a ‘yes’ or a ‘no’ is the only answer is the clearest way to present this; I’m pretty sure I’ve seen the problem stated that way somewhere. [/spoiler]

For the three-person variant, it’s possible to get the information you want in two questions.

You mean one question.

Does anybody remember what, exactly, Jennifer Connolly asked those guys in Labyrinth? I remember the scene but it’s been years since I’ve seen that movie and I don’t remember if she got the riddle right or not.

Labyrinth Script


Sarah: All right. Answer yes or no. Would he tell me that this door leads to the castle?
Alph: Uh… What do you think? Really? Yes.
Sarah: Then the other door leads to the castle, and this door leads to certian death.
Alph: He could be telling the truth.
Sarah: But then you wouldn’t be. So if you said he said yes, the answer is no.
Alph: I could be telling the truth.
Sarah: Then he’d be lying, and the answer would still be no.
Alph: Is that right?
Ralph: I don’t know. I’ve never understood it.
Sarah: No, it’s right. I’ve figured it out. I couldn’t do it before. I think I’m getting smarter. It’s a piece of cake. Aaaaahhh!!!

Well, if it can be done in one, it can be done in two, right?

I’ve seen the two question solution, but never just one.

It looks like she solved the riddle correctly. Maybe the oubliette is the correct way, and the other door would have dropped her into a pit of spikes or something.

By this logic either one could just remain silent. Therefore neither breaks the rules governing them and neither of them can be identified. There has to be some limit to what they can say and I think we can assume yes/no answers will be said.