Bob died, and met God and the Devil in his afterlife. He knew that God always spoke the truth and the Devil always lied. He did not know which one was which. He was allowed to ask one yes-no question which both would answer. If he succeeded in deducing the identities of the two entities, he would be sent to heaven. Otherwise, he would be sent to hell.

Bob had other plans. He wanted to have some fun. He asked a question that stumped God and the Devil. They could not answer it even though they knew the facts required to answer the question.

Impressed with his logical prowess, they decided that Bob would work with them for the rest of his afterlife. What question might he have asked to stump God and the Devil?

[SOLVED]

3 comments

Gemini6Ice solved this puzzle:

"What answer does God not give to this question?"

If God answers "Yes," then he has lied, and vice-versa.

By extension, the Devil is stumped because God is stuck in a paradox.

Eric Sosman solved this puzzle:

Bob addressed himself to the Entity carrying the four-pointed trident and pointed at the other Entity, the one reeking of odorlessness. "You are both omniscient, and know each other to the last degree, and know how the other would act in any circumstance. What, then, is His prediction of Your answer?"

There was an awe-ful silence. Then Bob got nervous and said "No, cancel that, ahem: P = NP?"

Susam Pal from cotpi added:

Here are two more possible solutions:

  • If I asked you, "Is 1 + 1 = 0?", would your answer be same as the answer to this question?
  • If I asked you, "Is 1 + 1 = 2?", would your answer be different from the answer to this question?

Credit

This puzzle is taken from folklore.

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