The unexpected hanging paradox or surprise test paradox is a paradox about a person's expectations about the timing of a future event which they are told will occur at an unexpected time. The paradox is variously applied to a prisoner's hanging or a surprise school test. It was first introduced to the public in Martin Gardner's March 1963 Mathematical Games column in Scientific American magazine.
There is no consensus on its precise nature and consequently a canonical resolution has not been agreed on.[1] Logical analyses focus on "truth values", for example by identifying it as paradox of self-reference. Epistemological studies of the paradox instead focus on issues relating to knowledge;[2] for example, one interpretation reduces it to Moore's paradox.[3] Some regard it as a "significant problem" for philosophy.[4]