Originally Posted by punkworld

Here's a logical riddle:

A man is sitting on death row, waiting for his execution. The judge, a cruel man with a sadistic sense of humor, who however always keeps his word, walks in one friday night, and says:
"Next week, we'll execute you. It will be on monday, tuesday, wednesday, thursday or friday. However, you won't know which one it will be... it will be a surprise."

The inmate panics and thinks all weekend about the fate awaiting him. Then, he figures out:
It is impossible that he will get executed on friday. After all, if he hasn't been executed until friday, he will know it's friday, and it won't be a surprise.
But, then it means it is impossible that he will get executed on thursday. After all, he knows he won't get executed on friday, so if he hasn't been executed by thursday, it won't be a surprise if he gets executed on thursday.
But, then it means it is impossible that he will get executed on wednesday. After all, he knows he won't get executed on friday or thursday, so if he hasn't been executed by wednesday, it won't be a surprise if he gets executed on wednesday.
But, then it means it is impossible that he will get executed on tuesday. After all, he knows he won't get executed on friday or thursday or wednesday, so if he hasn't been executed by tuesday, it won't be a surprise if he gets executed on tuesday.
But, then it means it is impossible that he will get executed on monday. After all, he knows he won't get executed on friday or thursday or wednesday or tuesday, so if he hasn't been executed by monday, it won't be a surprise if he gets executed on monday.

Having figured this out, the inmate rejoices, realizing that he won't be executed. Much to his surprise, somewhere in the middle of the next week on a gloomy afternoon, he gets lifted out of his bed and is hanged, the look of surprise still on his face.

How is this possible?