Full Text

surprise examination paradox

roy a. sorensen

Subject Philosophy » Epistemology

DOI: 10.1111/b.9780631192589.1993.x


A teacher announces that there will be a surprise examination next week. A clever student argues that this is impossible. ‘The test cannot be on Friday, the last day of the week, because it wouldn't be a surprise. We would know the day of the test on Thursday evening. This means we can also rule out Thursday. For after we learn that no test has been given by Wednesday, we would know the test is on Thursday or Friday – and would already know that it is not on Friday by the previous reasoning. The remaining days can be eliminated in the same manner.’ This puzzle has over a dozen variants. The first was probably invented by the Swedish mathematician Lennart Ekbom in 1943. Although the first few commentators regarded the reverse elimination argument as cogent, every writer on the subject since 1950 agrees that the argument is unsound. The controversy has been over the proper diagnosis of the flaw. Initial analyses of the student's argument tried to lay the blame on a simple equivocation. Their failure led to more sophisticated diagnoses. The general format has been an assimilation to better known paradoxes. One tradition casts the surprise examination paradox as a self-referential problem, as fundamentally akin to the Liar, the paradox of the knower , or Gödel's incompleteness theorem. The original talk of a surprise is read as a reflexive claim about unprovability. That is, the teacher's ... log in or subscribe to read full text

Log In

You are not currently logged-in to Blackwell Reference Online

If your institution has a subscription, you can log in here:


     Forgotten your password?

Find out how to subscribe.

Your library does not have access to this title. Please contact your librarian to arrange access.

[ access key 0 : accessibility information including access key list ] [ access key 1 : home page ] [ access key 2 : skip navigation ] [ access key 6 : help ] [ access key 9 : contact us ] [ access key 0 : accessibility statement ]

Blackwell Publishing Home Page

Blackwell Reference Online ® is a Blackwell Publishing Inc. registered trademark
Technology partner: Semantico Ltd.

Blackwell Publishing and its licensors hold the copyright in all material held in Blackwell Reference Online. No material may be resold or published elsewhere without Blackwell Publishing's written consent, save as authorised by a licence with Blackwell Publishing or to the extent required by the applicable law.

Back to Top