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<Paper uid="C92-1054">
  <Title>Redundancy in Collaborative Dialogue</Title>
  <Section position="1" start_page="0" end_page="0" type="abstr">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> It seems a perfectly valid rule of conversation not to tell people what they already know. Indeed, Grice's QUANTITY lllaxim has often been interpreted this way: Do not make your contribution more informative than is required\[f\]. Stalnaker, as well, suggests that to assert something that is already presupposed is to attempt to do something that is already done\[14\]. Thus, the notion of what is informative is judged against a background of what is presupposed, i.e. propositions that all conversants assume are mutually known or believed. These propositions are known as the COMMON GROUND\[10, 5\].</Paragraph>
    <Paragraph position="1"> The various formulations of this 'no redundancy' rule permeate many computational analyses of natural language and notions of eooperativity. However consider the following excerpt from the middle of an advisory dialogue between IIarry (h), a talk show host, and Ray (r) his caller 1.</Paragraph>
    <Paragraph position="2"> Example 1 : (6) r. uh 2 tax qunstionu.</Paragraph>
    <Paragraph position="3"> onu: since April 81 we have had an 85 year old lother living ~ith us.</Paragraph>
    <Paragraph position="4"> her only income has been social security plus approximately $3000 from a certificate O~ deposit and i wonder whatJs the situation as far as claiming her as a dependent or does thag income from the certificate of deposit rule her out as a dependent?  (7) h. yes it does.</Paragraph>
    <Paragraph position="5"> (8) r. IT DOES.</Paragraph>
    <Paragraph position="6"> (9) h. Y=UP THAT KHflCKS HER OUT.</Paragraph>
    <Paragraph position="7">  In standard information theoretic terms, both (8) and (9) are REDUNDANT. Harry's assertion in (9) simply paraphrases what was said in (7) and (8) and so it  pus w~s collected and transcribed by Marth~t Pollack anti Julia Hirschberg\[12\].</Paragraph>
    <Paragraph position="8"> cannot be adding beliefs to the cmnmon ground 2. Furthermore, the truth of (9) cannot be in question, for instead of 19), \[larry could not say Yup, but lhat doesn't knock her out. So why does Ray (r) in (8) RF~PEAT Harry's (h) assertion of it does, and why does lfarry PARAPHRASE himself and Kay in (9)? My claim is that mformationally redundant utterances (IRU's) have two main discourse functions: (1) to provide EVIUENCI~ to support the assumptions underlying the inference of mutual beliefs, (2) to CENTER a proposition, is. make or keep a proposition salient\[6\]. This paper will focus on (1) leaving (2) for future work. First consider the notion of evidence. One reason why agents need EVIDENCE for beliefs is that they only have partial information about: (1) the state of world; (2) the effects of actions; (3) other agent's beliefs, preferences and goals. This is especially true when it comes to modelling the effects of linguistic actions. Linguistic actions are different than physical actions. An agent's prior beliefs, preferences and goals cannot be ascertained by direct inspection. This means that it is difficult for the speaker to verify when an action has achieved its expected result, and so giving and receiving evidence is critical and the process of establishing mutual beliefs is carefully monitored by the conversants. null The characterization of IRU's ms informationally redundant follows from an axiomatization of action in dialogue that I will call the DETERMIniSTIC MODEL. This model consists of a number of simplifying assumptions such as: (I) Propositions are are either believed or not believed, (2) Propositions representing beliefs and intentions get added to tim context by the unilateral action of one conversant, (3) Agents are logically ormfiscient. (4) The context of a disconrse is an undifferentiated set of propositions with no specific relations between them. I claim that these assumptions nmst be dropped in order to explain the function of IRU's in dialogue.</Paragraph>
    <Paragraph position="9"> Section 2 discusses assumption (1); section 3 shows how assmnption (2) can be dropped; section 4 discusses (3); section 4.1 shows that some IRU's facilitate the inference of relations between adjacent propositions. 2\[8) is not realized with a rising question intonation. This will be discussed in sectiott 6.1.</Paragraph>
    <Paragraph position="10"> A~\]~s DE COLING-92, NAINrFES, 23-28 AO~&amp;quot; 1992 3 4 5 PROC. OF COLING-92, NANTES, AUG. 23-28, 1992</Paragraph>
  </Section>
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