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<Paper uid="E85-1014">
  <Title>apos;HOW &amp;quot;/0 RESTRICT AMBIGUITY 0F DIBCOURSE</Title>
  <Section position="2" start_page="0" end_page="94" type="intro">
    <SectionTitle>
INTRODUCTION
</SectionTitle>
    <Paragraph position="0"> The crucial problem in discourse analysis is the appropriate transposition of all expressions occurring in it, into reality (see, for instance, the framework provided by Kemp in (Kamp, 1981)). Even preliminary analysis shows that one real object can be identified by various surface constructions. This forces the necessity of dividing surface expressions into classes denoting identical individuals.</Paragraph>
    <Paragraph position="1"> The above problem can formally be stated as follows. To each discourse D we assign some reality which can be understood as a set ID of individuals (semantic discourse domain) together with a set of relations defined on ID. The semantic discourse domain can be interpreted twofold: 1.o as a set of real objects i.e., objects existing in actual world; 2 deg as a set of mental objects i.e., objects existing in language user's mind.</Paragraph>
    <Paragraph position="2"> Although the first interpretation is more natural, it leads to some ontological problems, concerning the distinction of fictitious and non-fictitious entities. Since there is no such distinction from linguistic perspective the second interpretation seems better motivated.</Paragraph>
    <Paragraph position="3"> &amp;quot;/he next step is to define syntactic discourse domain, denoted by S_, i.e., a set L) of discourse expressions referring to individuals (set of individuals). The mapping assigning individuals to syntactic expressions will be ca/led the reference function and denoted by R. F'orma/ly, R : S D 2 ID.</Paragraph>
    <Section position="1" start_page="0" end_page="94" type="sub_section">
      <SectionTitle>
Example
</SectionTitle>
      <Paragraph position="0"> (DI) John and Peter admire winter. They are often skiing together.</Paragraph>
      <Paragraph position="2"> We say that discourse expressions x and y a.re coreferencial, what we denote by xCy, if and only if they refer to the same set of individuals.</Paragraph>
      <Paragraph position="3"> Formally, for each x,y ~ S u xCy iff R(x)= R(y) It is readily verified that C is an equivalence relation. Obviously each equivalence class of C contains coreferentia/ expressions. The set of equivalence classes of C will be ca/led the reference sta~te of discourse and denoted by RSD.</Paragraph>
      <Paragraph position="4">  We can observe here that adding new utterance to the discour.~;e changes its  reference state. In this sense RSD is a dynamic notion Let us note also that the problem of anaphora solution can be regarded as defining the relation C for the whole discourse.</Paragraph>
      <Paragraph position="5"> Both the speaker, while constructin~ a discourse, and the hearer, while eunalysing it, try to achieve the identity of RSD at each step of the discourse. We argue in this paper that to accomplish this effect, the speaker has at his disposal (at each moment) a more restricted set of linguistic constructions than it seems intuitively. Let us notice that expressions belonging to one equivalence class have various syntactic shapes at different steps of discourse. It ca/'* be shown that the syntactic form of expressions at particular moments is not accidential, i.e., elements of indicated equivalence class are not interchangeable. P R O'I'O'I'YP E S Recent discourse theories provide several levels of larlguage analysis: morphological, syntactic, semantic and sometimes pragmatic. Each of these levels determines a characteristic set of notions and mechanisms. It is assumed here that the analysis of 82&amp;quot;, utterance on each levels of language should yield complete information obtainable by tools available on this level Classical anaphor resolvers act on semantic level on discourse analysis. ~Are take the position that for inflexion al languages the coreference relation can be partially described on the syntactic level An essential feature of this partial characteristic is defining the coreference relation quite apart from Peal individuals, i.e. without specyfing the reference function.</Paragraph>
      <Paragraph position="6"> &amp;quot;Po fix some ideas let us consider an utterance containing the noun phrases NPl, ..., NP . If there is no information regarding n coreference, all we can do is to assert that the coreference relation is included between the &amp;quot;minimal&amp;quot; relation, i.e., relation identified by the unit equivalence classes NP~ , ..., NP and the mcLximal one, i.e. adm,Ring in one nclass all number-gender agreeable phrases.</Paragraph>
      <Paragraph position="7"> We very seldom deal with such a situation in practice. Almost a/ways we can assign to an utterance a syntactic level information stating obligatory- coreference or obliqatory noncoreference of some expressions.</Paragraph>
      <Paragraph position="8"> The surface constructions carrying this kind of information with respect to pronouns and zero pronouns (in the case of elided subject) will be called prototypes. Ln other words prototypes can be regarded as syntactic means forcing obligatory coreference or obligatory noncoreference between pronouns or zero pronouns and other surface expressions.</Paragraph>
      <Paragraph position="9"> Let us consider few instances of prototypes. Because the ideas presented here are implemented for the Polish language, the notion of prototype will be illustrated with a number of Polish sentences. An elided subject specific for inflexional languages can be observed here. It is clenoted by (~ Because elided subject expresses some aspects of thematic continuity, its interpretation seems to be an important step during discourse analysis. English translations of presented examples preserve their syntactic shape. Unfortunately they are sometimes incorrect as English sentences.</Paragraph>
      <Paragraph position="10">  Peter, #I, ~2, ~)3 are coreferentiaL Another interpretation is unadm,ssible, in (I) we deal with obligatory coreference of expressions  (denoted by a - -- b).</Paragraph>
      <Paragraph position="11"> (2) ~I~2 podszeci% do okna, 4~4 ~skoczy~ ~)1. Woke up, q)2 came to the window, q)3 opened it and #4 jumped out.</Paragraph>
      <Paragraph position="12"> in (2), similarly as in (a) (co-ordinate clauses) and in (3), (4) (subordinate clauses) the only acceptable interpretation is explicitely showed.</Paragraph>
      <Paragraph position="13"> (3) Z~im Ca,~s~ea~2 zgasi~ ~wiat~o.</Paragraph>
      <Paragraph position="14"> Before 911 left, 912 turned the light off. (4) ~\].~_Z_gasi~ ~wiat~o, zanim....w~2 wyszedL 911 Turned the L~ght off, before ~2 left.</Paragraph>
      <Paragraph position="15"> The next examples concern the obligatory noncoreference of expressions (denoted by a+-b) (5) Ona lubi ja~ She likes her.</Paragraph>
      <Paragraph position="16"> (6) (~ zapyta~ Piotra,'~czy Jan p6jdzie do teatru.</Paragraph>
      <Paragraph position="17"> C/ Asked Peter, whether John would go to the theatre.</Paragraph>
      <Paragraph position="18">  (7) C/ Usiad~ do stc~u, a .Tan naleuI: mu wina. Sat at the table, und John poured him out some wine.</Paragraph>
      <Paragraph position="19"> The above examples pose the question of how the class of prototypes should be singled out. This problem can be solved by specifying a collection of rules concerning the obligatory coreference and obligatory noncoreference. The exact format of these rules is beyond the scope of this paper. For inflexional languages they depend on the type of considered sentence, the sentence-level functions of considered phrases and their syntactic shape. As a simple example of such a rule let us consider the basic criterion of excluding coreference: If the object is expressed by means of a reflexive pronoum, then it is coreferential with the subject; in other cases the referential identily of the subject and object is excluded.</Paragraph>
      <Paragraph position="20"> This criterion can be applied both for deterrninig coreferents of objects - blocking the subject, and in tesf/n~ the possible antecedents of the subject - blocking the objects. This is exactly the case we have in (5).</Paragraph>
      <Paragraph position="21"> THE RULE OF' RESTRICTED CHOICE A conclusive criterion of being a prototype results from analysing a given sentence it% isolation. If it is possible to assert or to exclude the referential identity of some expressions of the sentence, indepedently of its context then the sentence can be regarded as an instance of prototype. An essential feature of prototypes is that they are completely indistinctive and in this sense they are the most proper tool for expressing a certain relationship in the utterance. This strong relationship makes it possible to eliminate some interpretations, which in other cases should be regarded as probable too. If we agree that achieving unambiguity of discourse is the major goal both for the speaker and the hearer, then the non-application of prototype, as the most natural and efficient mea/qs of communication should be well motivated. When such a special reason is lacking, the speaker should apply a a prototype. Under this assumption the set of linguistic tools available to the speaker is restricted.</Paragraph>
      <Paragraph position="22"> The notion of prototype can be natural/y applied on the syntactic level of discourse anadysis to limit the number of hypotheses for further consideration. 13ut it can also be useful on the hi~her levels to interpret ambiguous discourses. Strictly speakin~ the properties of prototype suggest the general outline of interpreting ambiguous sentences, more precisely a method of orderin~ possible interpretations with respect to their plausibility. From the set of possible interpretations of a sentence, those that can be equivalently expressed by means of prototype, should be regarded as less plausible. The justification of this choice is clear: if the speaker wanted to point out such an interpretation, he would naturally achieve it by applying a prototype. In view of the obove we can formulate the rule of restricted choice. It states that whenever it is possible the application of a prototype should be preferred.</Paragraph>
      <Paragraph position="23"> It is irrportant to notice that the rule of restricted choice can be viewed from the perspective both of the speaker contructing the discourse and the hearer modelling it. The speaker should apply prototypes whenever it is possible. The hearer should take this fact into consideration.</Paragraph>
      <Paragraph position="24"> Let us try to interpret the concrete sentences with the help of the rule of restricted choice.</Paragraph>
      <Paragraph position="25">  Before ~ll left, John turned the light off. (~ denotes the reference to the context).</Paragraph>
      <Paragraph position="26"> But the first interpretation can be expressed by means of prototypes.</Paragraph>
      <Paragraph position="27"> (Pl) Zanim ~I ~Aryszed{, @2 zgasit ~wiat~o. Before ~1 left, ~2 turned the Light off.</Paragraph>
      <Paragraph position="28"> (P2) Jan zanim wyszedt, ~1 zgasit gwiatto. John before left, ~1 turned the light off. According to the rule of restricted choice the first interpretation should be regarded as less probable (note that it can be expressed by prototype). Hence the second interpretation should be chosen.</Paragraph>
      <Paragraph position="29">  Another example is more complicated.</Paragraph>
      <Paragraph position="30"> (11) Zanim o__.nn wyszed~, ~I zapy~ak ~eo, czy #2 p6jdzie do kina.</Paragraph>
      <Paragraph position="31"> Before he leftmasc , @I, had asked him, whether ~2 would have gone to the cinema.</Paragraph>
      <Paragraph position="32"> In the embedded clause 03. zapy%a~ gO there acts the rule of obligatory noncoreference excluding the referentia/ identily of subject and object in this sentence: Zanim on wyszed~, @~zapytakj~o, czy ~2 p6jdzie do kina.</Paragraph>
      <Paragraph position="33"> According to our definition the above sentence is an instance of a prototype.</Paragraph>
      <Paragraph position="34"> Excluding the coreference of pointed expressions decreases the numer of possible interpretations, but does not clear up all referential relationships in this ambiguous sentence. Although there are no further syntactic premises to resolve this ambiguity we can specify the less probable interpretation by appying the rule of restricted choice. If the speaker wanted to express the following sense:  (12) Zanim X wyszeck%, X zapy%a.% go, czy @1. p6jdzie do kineu .</Paragraph>
      <Paragraph position="35"> he should have used the following (structural) prototype: (13) Z~im C/~1 ~apyt~ go,  czy ~2 p6jdzie do kina.</Paragraph>
      <Paragraph position="36"> (In such a sequence of clauses in the sentence the rule of obligatory coreference demandes that C/ and @1. shou/d be identified). It follows therefore that the interpretation: (3.4) Zanim on wyszedku.~l zap vta~ go, czy ~2 p6jdzie do kina.</Paragraph>
      <Paragraph position="37"> is the less probable and should be computed as the last one.</Paragraph>
    </Section>
  </Section>
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