Conversational Implicatures in Indirect Replies

CONVERSATIONAL IMPLICATURES IN INDIRECT REPLIES Nancy Green Sandra Carberry Department of Computer and Information Sciences University of Delaware Newark, Delaware 19716, USA email: green@cis.udel.edu, carberry~cis.udel.edu Abstract I In this paper we present algorithms for the interpretation and generation of a kind of particu- larized conversational implicature occurring in cer- tain indirect replies. Our algorithms make use of discourse expectations, discourse plans, and dis- course relations. The algorithms calculate implica- tures of discourse units of one or more sentences. Our approach has several advantages. First, by taking discourse relations into account, it can cap- ture a variety of implicatures not handled before. Second, by treating implicatures of discourse units which may consist of more than one sentence, it avoids the limitations of a sentence-at-a-time ap- proach. Third, by making use of properties of dis- course which have been used in models of other dis- course phenomena, our approach can be integrated with those models. Also, our model permits the same information to be used both in interpretation and generation. 1 Introduction In this paper we present algorithms for the interpretation and generation of a certain kind of conversational implicature occurring in the follow- ing type of conversational exchange. One partici- pant (Q) makes an illocutionary-level request 2 to be informed if p; the addressee (A), whose reply may consist of more than one sentence, conversa- tionally implicates one of these replies: p, "-p, that there is support for p, or that there is support for "-p. For example, in (1), assuming Q's utterance has been interpreted as a request to be informed if A went shopping, and given certain mutual beliefs e.g., that A's car breaking down would normally e sufficient to prevent A from going shopping, and i We wish to thank Kathy McCoy for her comments on this paper. ~i.e., using Austin's (Austin, 1962) distinction between locutionary and il]ocutionary force, Q's utterance is intended to function as a request (although it need not have the gram- matical form of a question) that A's reply is coherent and cooperative), A's re- ply is intended to convey, in part, a 'no'. (1) Q: Did you go shopping? A: a. My car~s not running. b. The timing belt broke. Such indirect replies satisfy the conditions proposed by Grice and others (Grice, 1975; Hirschberg, 1985; Sadock, 1978) for being classi- fied as particularized conversational implicatures. First, A's reply does not entail (in virtue of its conventional meaning) that A did not go shopping. Second, the putative implicature can be cancelled; for example, it can be denied without the result sounding inconsistent, as can be seen by consider- ing the addition of (2) to the end of A's reply in (1.) (2) A: So I took the bus to the mall. Third, it is reinforceable; A's reply in (1) could have been preceded by an explicit "no" without destroy- ing coherency or sounding redundant. Fourth, the putative implicature is nondetachable; the same re- ply would have been conveyed by an alternative re- alization of …

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