I apologize in advance for my punctuation being all messed up on this keyboard. This question could be a GD, but its strictly a famous logic problem really.
Basically, the problem is this.
A very intelligent man is told that he will be executed. He is told that there will be two conditions for this execution to take place.
- The execution will happen on either Monday, Tuesday, Wednesday, Thursday, or Friday of the next week.
- He will not know which day it will be until the day of the execution. In other words, he cannot know the day before that the next day is the day of his execution.
The paradox is that if the man lives to see Thursday, and he is not executed that day, then, being intelligent, he will know that Friday is the day of his execution. So he cannot be executed on Friday because that would fail condition 2. Unfortunately, the logic continues. Given that he cannot be executed on Friday, if the man lives to Wednesday without being executed that day, he already knows that he cannot be executed on Friday, so he knows that he will be executed on Thursday, which in turn means that he can´t be. The logic continues to rule out every single day, including Monday.
But, as the story goes, the day of execution comes, and the man does not know the say beforehand. The question is whether this could really happen.
One possible wrinkle is the use of a computer that randomly selects the day of execution. The computer IGNORES the second rule in picking the day. This fact can either be told to the man or not.
This definately changes the situation somewhat, but I don´t think it resolves the paradox. In fact, it seems to make the underlying paradox clearer, because now we see the dilemna from the perspective of the computer programmers. They can either tell the man the truth about how the computer selection process works or lie about the process as long as the original two conditions hold. And the selection process can either be fully random, or pick from a smaller set of days, such as only M thru Th. But it still seems that no matter how they design the process, and no matter what they tell the man, the paradox remains. Because, of course, if the computer randomly picks Friday, then it must start over. The man knows that even a random selection process cannot be designed to be allowed to pick Friday. So it really is picking among M thru T. But it can´t be allowed to pick Thursday, because if it did, it would have to start over… and so on.
The really cheap solution to this problem is, of course, that someone knocks the man unconcious for a few days, then wakes him up to die on the day of his execution.
