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. 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; for example, one interpretation reduces it to Moore's paradox. Some regard it as a "significant problem" for philosophy. Description The paradox has been described as follows: Other versions of the paradox replace the death sentence with a surprise fire drill, examination, pop quiz, A/B test launch, a lion behind a door, or a marriage proposal before moving to Seattle. Logical school Formulation of the judge's announcement into formal logic is made difficult by the vague meaning of the word "surprise". An attempt at formulation might be: The prisoner will be hanged next week and the date (of the hanging) will not be deducible the night before from the assumption that the hanging will occur during the week (A). Given this announcement the prisoner can deduce that the hanging will not occur on the last day of the week. However, in order to reproduce the next stage of the argument, which eliminates the penultimate day of the week, the prisoner must argue that his ability to deduce, from statement (A), that the hanging will not occur on the last day, implies that a second-to-last-day hanging would not be surprising. But since the meaning of "surprising" has been restricted to not deducible from the assumption that the hanging will occur during the week instead of not deducible from statement (A), the argument is blocked. This suggests that a better formulation would in fact be: The prisoner will be hanged next week and its date will not be deducible the night before using this statement as an axiom (B). Fitch has shown that this statement can still be expressed in formal logic. Using an equivalent form of the paradox which reduces the length of the week to just two days, he proved that