Friday Diversion: the Unexpected Tigering Paradox

A City fan makes two statements to Andy Hughes:

You will be tigered to death at noon one day next week, Monday through Friday. The tigering will be a surprise to you: you won't know the day it will happen until the tiger arrives at Colney at noon that day.

Andy Hughes reflects on these statements, and then smiles. "If the tigering were on Friday," he thinks, "then it wouldn't be a surprise; for I would know by Thursday night that I was going to be tigered on Friday, since no tigering had yet occurred and only one day was left. So the tigering can't be on Friday."

"But," he continues, "then the tigering can't be on Thursday either. If it were, then it wouldn't be a surprise either. For I would know on Wednesday night that I was going to be tigered on Thursday, since no tigering had yet occurred and only two days were left, one of which (Friday) I already know cannot be tigering day. So a Thursday tigering is impossible too."

Similar reasoning shows that the tigering can't be on Wednesday, Tuesday, or even Monday! He returns to Colney confident in his safety.

The next week, the tiger arrives at noon on Wednesday - an utter surprise. Everything the City fan said has come true. Where is the flaw in the Hughes's reasoning?

Posted By: Partial Angler, Feb 3, 14:33:27