A competent logician was traveling home down an unfamiliar road. As he approached a fork heading in two different directions, he noticed a lone figure standing directly between the two routes. The person was dressed in a full suit of armor, holding a sword.
As the logician got closer, he recognized the stranger as one of the accursed twins that he had encountered previously at another crossroads. With them being identical he could not tell which twin stood before him, the one who always spoke the truth or the one who could only ever lie.
Being familiar with the brothers, he approached and waved.
“Hello sir! I believe we’ve met before, do you remember me?”
The man looked at the logician, but did not say anything.
“Would I be correct in assuming that you are the knightly brother who always tells the truth?”
The brother continued to stare at the logician, offering no indication of an answer. The logician wasn’t sure if he had heard the question.
“Are you the knight, sir?”
“Yes, I’m the truth-telling brother,” came the courteous reply.
“You’re not the knave are you?”
“I am not,” the stranger responded immediately. It occurred to the logician that if he were, that was hardly the correct question to ask.
Considering that there was no one else around, he decided it would be best to attempt to deduce which twin this was, so that he could find the correct way to get home.
“Sir, do you know the correct way to go to get to town?”
The armored man did not respond to the question.
“I say, if I asked you for the correct route to take to get to town, would you point the way?”
“Yes, of course I would,” he replied graciously.
“Excellent! Which way is it?”
Again the man simply stared blankly at him.
“Do you have troubling hearing me?”
No reply was forthcoming.
“Will you please give me the answers I seek?”
“Yes,” the stranger repeated.
The logician started to get annoyed. This person could clearly answer his questions, but with him deciding to answer some questions and not others he could not be sure whether he could correctly identify which twin he was.
“Which way should I take to get to town?”
Again the brother did not say a word.
“Do I take the road to my left to get to town?” The man said nothing.
“Do you have some sort of issue with responding to my questions?”
“No, of course not!” Came his ready reply.
“Very well, do I take the road to my right to get to town?” No response.
The logician threw his hands up in frustration “Argh! Will you please just tell me what I want to know?”
“I will,” the man before him intoned.
“You say that, but then you do not respond to my questions! You say you’re a knight, but you do not have any honor… if only your brother were here as well then this would be much easier!”
As he watched, the man before him burst into tears, which took the logician aback. In deciding whether this person was a liar or a truth-teller, he had momentarily forgotten that he was a human.
“I'm ever so sorry my friend, is your brother ok?” the logician ventured.
The sobbing man looked up at him, his eyes pleading. No words were said, but the logician suddenly thought he understood the predicament this person was in, and what was causing him to only answer certain questions.
“Is the lying twin ok?” He asked.
The brother before him shook his head. “No, he’s not.”
With his suspicions confirmed, the logician sat with the brother for a while to comfort him. He then asked one last question of the twin, which he knew would be answered, and then the logician headed home down the left fork.
For full points, one must answer:
What was the predicament the twin was in, causing him to be unable to answer all of the questions asked?
What question did the logician finally ask to find the correct route home?
Which twin could it have been that he had been talking to?