2008 09 30
A logician vacationing in the South Seas finds himself on an island inhabited by the two proverbial tribes of liars and truth-tellers. Members of one tribe always tell the truth; members of the other always lie.
He comes to a fork in a road and has to ask a native bystander which branch he should take to reach a village. He has no way of telling whether the native is a truth-teller or liar. The logician thinks a moment and then asks one question only. From the reply, he knows which road to take.
What question does he ask?
…For our purposes here, weâ€™ll assume that the answer is confined to a single â€œyesâ€ or â€œno.â€
I had heard this one years ago, and cannot now remember if I figured it out on my own or not. (Probably not, knowing my limitations.)Â The only snag is that either I’m wrong, or else the last instruction—“the answer is confined to a single â€œyesâ€ or â€œno.â€”—is slightly misleading. Here’s a hint: the instruction is playing fast and loose with the use/mention distinction. Oh, and if my solution works, then there are actually two questions he could ask.
Anyway, I submitted an answer.Â We’ll see what happens.
Howls of outrage (5)