Fork in the Road...

CamelMenthol

Welcome to A2K

You have not quite asked the classic question.

....The man/native at the crossroads comes from either a tribe of constant liars, or from a tribe of truth tellers.....

The question to ask is "which way would a guy from the other tribe tell me to go to the city ?"...and you take the other road.

the way i heard it was, you ask, "if i were to ask you if this road goes to the city, would you say yes?" and if he says yes, take that road.

yitwail

same principle....yours is neater !

thanks, but i simply heard it in a logic class a long time ago, whereas your solution was probably original.

What if THIS way goes to death and the man is a liar .... He would say Yes and you will take that road and die....

ok. let's do this one step at a time. as you say, this road leads to death. so if you just ask if it goes to the city, he will say yes.

but if instead you ask, if i asked you if it goes to the city, would you say yes? then he will answer no, because he must lie about the answer he would give if you just asked the question.

so, his answer is no, and you take the other road.

Sorry guys, I still don't get it.

Going back to the original question; as asked.

One man - Truth/Lies.
Two paths - City/Death.
One question.

How about:

"If you were a liar and I asked you which road leads to the city, which path would it be?"


a) If he was the liar he would have to point to Death.

b) If he told the truth, he would have to give the same answer as the liar.

Either way you take the opposite road.


Apologies, if that was what has already been said, I am a bit slow

But yitwail's solution satisfies the problem as posed, whereas yours satisfies the "classic" problem only. The current problem doesn't mention an alternate tribe.

makr

I thought it was obvious that the principle is an "embedded question" in each case. Each asks for a truth value of a truth value. Both versions refer to the rule ~(~P)=P in the case of the liar, thereby eliminating the need to determine to the status of who gives the answer.

You're right. I'm just pointing out that the one question isn't a solution to the problem that was posed.

Point taken. My original perception was that the question had been mis-stated.