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No Surprises

  • Ian WellsEmail author
Original Research


The surprise exam paradox is an apparently sound argument to the apparently absurd conclusion that a surprise exam cannot be given within a finite exam period. A closer look at the logic of the paradox shows the argument breaking down immediately. So why do the beginning stages of the argument appear sound in the first place? This paper presents an account of the paradox on which its allure is rooted in a common probabilistic mistake: the base rate fallacy. The account predicts that the paradoxical argument should get less and less convincing as it goes along—a prediction I take to be welcome. On a bleaker note, the account suggests that the base rate fallacy may be more widespread than previously thought.



My foremost thanks go to Stephen Yablo and Roger White for invaluable feedback on the ideas in this paper. I also want to thank Andrew Bacon, Alex Byrne, Nilanjan Das, Ned Hall, Justin Khoo, Bernhard Salow, Robert Stalnaker and audiences at Cambridge University, Caltech and MIT.


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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.Massachusetts Institute of TechnologyCambridgeUSA

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