a man is walking through a town where the people either always tell the truth or always tell a lie. He comes to a fork in the road and does not know which way to go to get to the place he needs to go. What question could he ask a townsperson to get the correct direction?
I think you need to be able to ask two questions to find out what is the correct road to take. First you need to ascertain if you are talking to a truth teller or a liar. The 2nd question should be able to send you on your way to your destination.