To make up for last month, I am posing a question that is both humorous and thought provoking at the same time. There are multiple ways to approach this problem, and it is surprisingly difficult to articulate on exactly what is amiss. Good luck everyone, here is the problem:
Judge Wright has a reputation for always being right. Standing before him is a condemned prisoner, who turns out to be a logician. Judge Wright decides to have some fun with him, and says, “You will be hanged at noon on one day this week, and it will come as a surprise to you. You will not know until the executioner comes knocking on your cell door at 11:55am the day of the execution. It is 4pm Sunday now, so it will happen by noon on Friday at the latest.”
The prisoner carefully considers Judge Wright’s comments. He reasons that Friday cannot be the day of execution, because being the last possible day of execution, what kind of surprise would that be? That rules Friday out completely. How about Thursday? Well, Friday is out, so Thursday is now the last possible day of execution. But again, it wouldn’t come as a surprise either. So Thursday is also out. By similar reasoning, Wednesday, Tuesday, and Monday are all logically ruled out. The only conclusion the prisoner could come to, is that Judge Wright made a rare mistake, and he will not be hanged at all.
At 11:55am Thursday, the executioner came knocking on the cell door. And sure enough, it came as a total surprise to the prisoner. Judge Wright had been right all along 🙂
Question: What is wrong with the prisoner’s reasoning?
*** Warning: It may seem like a frivolous question, but rest assured it is not as easy as it may seem ***