 Lying is a complicated matter, but what’s puzzling about sentences like the first one of this essay isn’t essentially tied to intentions, social norms, or anything like that. Rather, it seems to have something to do with truth, or at least, some semantic notion related to truth. The puzzle is usually named ‘the Liar paradox’, though this really names a family of paradoxes that are associated with our type of puzzling sentence. The family is aptly named one of paradoxes, as they seem to lead to incoherent conclusions, such as: “everything is true”. Indeed, the Liar seems to allow us to reach such conclusions on the basis of logic, plus some very obvious principles that have sometimes been counted as principles of logic. Thus, we have the rather surprising situation of something near or like logic alone leading us to incoherence. This is perhaps the most virulent strain of paradox, and dealing with it has been an important task in logic for about as long as there has been logic.