MovieChat Forums > Labyrinth (1986) Discussion > The Door Riddle, take three: How does on...

The Door Riddle, take three: How does one solve it?

posted 2 years ago by ExTechOp (2770)
4 replies | jump to latest

The solution is so simple: ask one guard what the other will say. The answer MUST be a lie.

BUT

What sort of reasoning leads to that solution?

I have to admit, I was told the answer, and it seems so obvious once you know it. The answer is false whether it's a lie about the truth or the truth about a lie.

But how does one come up with that solution?

I've seem posts referring to truth tables, but don't those require that you know the input first? Truth tables work just fine for the Monty Hall Dilemma, for example, because you know all the possible outcomes AND all the possible choices.

Did anyone reach the solution deductively? Seems everyone who's solved it themselves used inductive or abductive reasoning, and just sort of "stumbled upon" it.

[–] moviechatterer (16052) 2 years ago

I was told the solution too , dont know if i'd have ever got there .

I cant help thinking that the fact that
-2 x -2 = 4
but 2 x 2 = 4 too , might be helpful in the reasoning . somewhere .

something about making a number +ve whether its +ve or negative.

[–] ExTechOp (2770) 2 years ago

That negative/positive thing's a good way to look at it. So ...

-2 x 2 = -4
2 x -2 = -4

In other words, the product is negative as long as there's a negative multiplier or a negative multiplicand (had to look that term up!).

Or, if I recall my college algebra logic lessons correctly, a false statement combined with a true statement gives a false compound statement. "Apples are red AND oranges are mammals," is false.

I suppose from those principles, one could deduce that combining both guards' answers would give you a predictably false statement

But that's theoretical, since I didn't get there myself

[–] CrabgrassWilly (1616) 2 years ago

An axe to the face of each of those doors should do the trick.

[–] quartz (482) a year ago

I felt like they spent a lot less time on this scene than they could have, they could have made it into a bigger more in depth scene, but actually only spent a few moments on it