Normal State Implicature

NORMAL STATE IMPLICATURE Nancy L. Green Department of Computer and Information Sciences University of Delaware Newark, Delaware 19716, USA Abstract In the right situation, a speaker can use an unqual- ified indefinite description without being misun- derstood. This use of language, normal slate im- plicature, is a kind of conversational implicature, i.e. a non-truth-functional context-dependent in- ference based upon language users' awareness of principles of cooperative conversation. I present a convention for identifying normal state implica- tures 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 Introduction 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 un- derstood as meaning (lb). The goal of this paper is to formally describe such uses of language. 1 1A similar use of language is noted in [McC87]. Mc- Carthy (pp. 29-30) discusses the problem of brid~ng the gap between a "rather direct [translation] into first order logic" of a statement of the Missionaries and Cannibals puz- zle, and a representation suitable for devising a solution to the puzzle. For example, if the puzzle statement mentions that '% rowboat that seats two is available" and doesn't say that anything is wrong with the boat, the problem-solver may assume that the boat doesn't leak, has oars, etc. Mc- Carthy proposes a general-purpose method for formalizing common sense reasoning, "circumscription", to solve the problem. Also, a similar use of language is described in [GriT5] (p. 51): "A is standing by an obviously immobilized car and is approached by B; the following exchange takes place: A: I am out of petrol. B: There is a garage round the corner. ... [B] implicates that the garage is, or at least may be open, [has petrol to sell], etc." That tiffs use of language 89 1. (Clerk A:) May I help you? a. (Customer B:) I'd like to see a parrot. b. I [the speaker] would like to see a live parrot. c. 3 p:PARROT REQUEST(B,A,SIIOW(A,B,p)) d. 3 q:[A p:PARROT LIVE(p)] REQUEST(B,A, SHOW(A,B,q) One problem is that (la) (i.e. its putative representation in (lc)) does not entail (lb) (i.e. its putative representation in (ld)). 2 Another problem is the context-dependence, both spatio-temporal and linguistic, of the relationship of (lb) to (la). In a different spatic~temporal context, such as in a china shop, a speaker might use (la) to convey (2) rather than (lb). 2. I [the speaker] would like to see a porcelain parrot. In a different linguistic context, such as if the cus- tomer had said (3a) following (la), she would not involves the use of language I have illustrated in (1) can be seen by considering a situation identical to …

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