Why it is impossible for you to have a surprise test next week
Imagine you are this small south east Asian boy in a crippling portable school building, your teacher informs the class about a test next week, but you don't which day the test will take place on, only that it will happen some time during the next week. But the thing is that it is virtually impossible for the test to be a surprise. To explain this paradox we have to imagine that it's Thursday and the test has not taken place yet, so you conclude the test is going to take place on Friday, therefore not making it a surprise, which means the test cannot take place on this day. So in order to keep the test a surprise we have to remove Friday as a possibility. That's it right? Wrong, we have not solved the problem, since we now know the test cannot take place on Friday, when Wednesday arrives and if the test has not occurred yet, we could conclude that the test will happen tomorrow on Thursday, So again, in order to keep the test a surprise we have to remove the possibility of