HERE’S A RECENT twist on an old type of logic puzzle. 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 a liar. The logician thinks a moment,
then asks one question only. From the reply he knows which road to take. What
question does he ask?