Some commentators have noticed a similarity between a pared down version of the paradox of the surprise examination and Moore's paradox. What they have failed to notice is that the real similarity with Moore lies in the students' acceptance of the teacher's announcement not in that announcement itself. I shall attempt to bring Wittgenstein's little discussed discussion of Moore's paradox to bear on the surprise examination and to argue that this yields a solution to the latter paradox that satisfies all reasonable criteria of satisfactoriness. A variant of the Moore paradox, equally susceptible to the Wittgensteinian treatment, underlies Gregory Kavka's Toxin paradox which, though superficially quite dissimilar to the surprise examination, has been shown by Roy Sorensen to belong in the same family. Since it too falls to the solution here advocated, there is some reason to believe that that solution is powerful and true. The surprise examination paradox goes like this: A teacher, at school's end on Friday, says to her class 'I'm going to give you a surprise examination one day next week'. A bright pupil figures out that next Friday can't be that day since, if no exam is given by close of school on Thursday, there would be only one day left for the exam; students would know this and therefore they would expect the exam that day - it wouldn't be a surprise. But, with Friday ruled out, we can go through the same kind of reasoning to rule out Thursday: by Wednesday evening, with Friday already ruled out as surprise day, only Thursday would remain as possible, so the exam would have to be given on that day; no surprise. A similar line of argument rules out Wednesday, Tuesday and Monday as possible exam days, hence the argument shows that the surprise exam promised by the teacher cannot take place. But then, on, say, Tuesday, the teacher waltzes into the class and dishes out the exam papers. This comes as a great surprise to the students, especially those who regarded the clever student's argument as impeccable. Clearly it's not impeccable. But where does it go wrong?
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Jul 1, 1997
Luc Bovens 
