A Liar sentence is a sentence that, paradoxically, we cannot evaluate for truth in accordance with classical logic and semantics without arriving at a contradiction. For example, consider L
If we assume that L is true, then given that what L says is ‘L is false,’ it follows that L is false. On the other hand, if we assume that L is false, then given that what L says is ‘L is false,’ it follows that L is true. Thus, L is an example of a Liar sentence.
Several philosophers have proposed that the Liar paradox, and related paradoxes, can be solved by accepting the contradictions that these paradoxes seem to imply (including Priest 2006, Rescher and Brandom 1980). The theory that there are true contradictions is known as ‘dialetheism’ and we may call this the ‘dialethic solution.’ One standard response to the dialethic solution to the Liar paradox and related paradoxes has been to attempt to develop new ‘revenge’ versions of the paradoxes that are not subject to the dialethic solution (e.g. Parsons 1990, Restall 2007, Shapiro 2007).