Grelling-Nelson paradox

A paradox of self-reference, where, supposing that every man either shaves himself or is shaved by the barber, and the barber shaves all and only the men who do not shave themselves, then it is impossible to determine who shaves the barber.

plural of liar paradox

Alternative form of twin paradox

A paradox arising from the question of what constitutes evidence for a statement. Observing objects that are neither black nor ravens may formally increase the likelihood that all ravens are black, even though, intuitively, these observations are unrelated.

Hempel's paradox

A thought experiment involving a game between two players, one of whom purports to be able to predict the future. The first player has to try to maximize winnings by choosing one of two boxes of money; however, the amount won also depends on whether a prediction made about the choice by the other player proves to be true.

A particular paradox in mathematical logic; the type-theoretic analogue of Russell's paradox from set theory.

plural of Epimenides paradox

A form of self-referential logical paradox associated with statements of the form "All Cretans are liars" (spoken by Epimenedes, himself a Cretan, who must therefore be lying).