Numberplay: Logic Postponed - NYTimes.com Life imitates Art. This Numberplay blog post was postponed and the day of its actual appearance left open-ended. This was not intentional, but it so resembles a classic logical paradox on postponement, that I can't resist making that the subject of this post. On a Friday afternoon, a teacher announces that the students will have a surprise test someday next week. On the weekend, one student thinks "If the exam were to be on Friday and if we still haven't had the exam by Thursday, we'll know what day the exam is to be, so it won't be a surprise. But if the test cannot be on Friday, then Thursday will be the last day to have the test and if we still haven't had the exam by Wednesday, we'll know it's on Thursday. So again, it won't be a surprise. He keeps doing this and concludes that they can't have a test next week. Thursday comes and they have a test, and the students are obviously surprised. What is the flaw in the student's argument? Just to round things off, here's another puzzle on postponed logic. A law school professor (P) took pity on a brilliant student (S) who was struggling financially, and was therefore in danger of dropping out. P made S the following offer. I'll pay your law school tuition. Just pay me back in full when you win your first case. The student accepted the offer, and graduated with honors. However, he decided to become a law professor like his mentor, with whom his relations had since soured. Since S never became a practicing lawyer and never won his first case, he figured he didn't have to pay back his professor. P was extremely frustrated by this, but suddenly had a brilliant idea. He filed a suit against S for breach of contract. The next day P confronted S in the hallway. "Now you'll have to pay me no matter what happens," said P. "If I win, the court will order you to do so, and if I lose, well, you've won your first case, so you have to pay up." "On the contrary sir," said S, "now I don't ever have to pay you back. If I win, the court will declare our contract null and void, and if I lose, well, I haven't yet won my first case. Who is right? That's all for now, folks. I'll see you again next week - I'm not saying when!