Normal State Implicature

In the right situation, a speaker can use an unqualified indefinite description without being misunderstood. This use of language, normal slate implicature, is a kind of conversational implicature, i.e. a non-truth-functional context-dependent inference based upon language users' awareness of principles of cooperative conversation. I present a convention for identifying normal state implicatures which is based upon mutual beliefs of the speaker and hearer about certain properties of the speaker's plan. A key property is the precondition that an entity playing a role in the plan must be in a normal state with respect to the plan. 1 I n t r o d u c t i o n In the right situation, a speaker can use an unqualified indefinite description without being misunderstood. For example, a typical customer in a typical pet shop who said ( la) in response to the clerk's question in (1) would expect to be understood as meaning (lb). The goal of this paper is to formally describe such uses of language. 1 1A similar use of l anguage is no ted in [McC87]. McCa r thy (pp. 29-30) discusses the p rob l em of b r i d ~ n g the gap be tween a " ra ther direct [ translat ion] into first order logic" of a s t a t e m e n t of the Miss ionar ies a n d Canniba l s puzzle, and a r ep re sen ta t ion sui table for devis ing a solut ion to the puzzle. For example , if t he puzzle s t a t e m e n t men t ions t ha t '% rowboat t h a t seats two is available" a n d doesn ' t say t ha t a n y t h i n g is wrong wi th the boa t , the problem-solver may assume that the boat doesn't leak, has oars, etc. McCar thy proposes a general-purpose method for formalizing common sense reasoning, "circumscription", to solve the