Semantic reasons

An analysis of a predicate normally takes the form of a condition that is both necessary and sufficient for the predicate's application. Here I consider the idea, due originally to Friedrich Waismann, that semantic analyses might include conditions that are defeasible, and so allow for exceptions. Analyses of this sort can be expressed in nonmonotonic logic, a post-Waismann development. I'll argue that defeasibility makes analysis tractable, without making it trivial. I'll also show that a defeasible account of vague predicates can predict our intuitions about particular cases (for instance, that a seven-foot person counts as tall) without drawing artificial boundaries.