Null vs. Overt Subjects in Turkish Discourse: A Centering Analysis
The purpose of this study is to explore an aspect of discourse coherence which involves anaphoric relations between utterances with special emphasis on subjects in Turkish. Based on an analysis of published narratives, three complementary and interrelated questions are addressed concerning discourse anaphora: 1. Which expressions are available for subsequent definite reference? 2. What factors determine the most salient entity in Turkish among a set of potential antecedents for subsequent definite reference? 3. What are the functions of a particular referential expression (null vs. overt pronouns vs. full NPs), depending on appropriate discourse conditions? An exploration regarding question 1. indicates that, while some NPs evoke discourse entities, other NPs do not. These two types of NPs represent referential and nonreferential expressions and they can function as antecedents for definite and indefinite nonspecific anaphora, respectively. The distinction between null and overt pronouns in Turkish is that only the former can be in an anaphoric relationship with a nonreferential antecedent. Overt pronouns, on the other hand, are sensitive to referent identity, they must have the same referent with their antecedents. In other words, overt pronouns are strictly coreferential, while null pronouns are not constrained in this way. The rest of the study investigates answers to questions 2. and 3. in instances where null and definite subjects alternate as definite anaphors. Centering Theory provides a cognitively plausible and computationally tractable framework for such an analysis with its precise rules which rely on linguistic knowledge constraining inferencing. As formulated in Centering Theory, each utterance contains a set of potential antecedents for reference in the subsequent utterance, i.e. a set of forward-looking centers (Cfs),that are ranked on the basis of their salience. The most salience entity in the Cf-list, the preferred center (Cp) is the entity that is predicted to become the backward-looking center in the subsequent utterance. The singleton backward-looking center (Cb) is taken to be the topic of the current utterance, i.e. the entity at the center of attention. Centering transitions, which model the dynamic attentional state in a discourse segment, are obtained by analyzing each adjacent pair of utterances. The functions of referential expressions in subject position are determined on the basis of Centering transitions. The results show that Turkish subject types pattern neatly and categorically when these transitions are taken into account. A brief discussion of language-specific and universal aspects of discourse anaphora is also included in the study.