the unexpected hanging

After the logician was convicted of murdering his wife, the judge sentenced him to hanging. The hanging was to occur the following week, but the judge added that the exact day of the hanging would be a surprise. The logician would not know the day until the executioner arrived at the prison cell.

The logician began pondering the sentence even as he was being led to the cell. He couldn't be hanged on Saturday, because if he were still alive at the end of Friday he would know before the executioner arrived that the hanging would occur on Saturday. Therefore, he couldn't be hanged on Friday: knowing that Saturday was out, if he were still alive on Thursday night, he would know before the executioner arrived that the hanging would occur on Friday. Therefore, he couldn't be hanged on Thursday...

Continuing in this manner, the logician had eliminated all the days of the week by the time he was locked in his cell. He was exuberant, knowing he could not be hanged after all.

Thus when the executioner arrived on Wednesday morning, the logician was utterly surprised.