Lost Intuitions and Forgotten Intentions

1 Overview To provide context for the discussions of centering that appear in this volume, we review our previous research on global focusing and centering and discuss central unsolved problems in the theory of centering. This paper does not provide a comprehensive review of work on centering, as this volume in its entirety serves that purpose. Rather we present our view of the history of centering and our perceptions of the most important areas for future work. The paper begins with a description of the intuitions underlying our previous research, a statement of the intended properties of the attentional state models and proposed theories, and the major claims made. We then look to the future development of centering and argue brieey for additional empirical research, analysis of more complex types of discourse, and more detailed examination of the interaction of centering with other discourse processes at both the local and global levels. 2 Original Intuitions and Intentions Grosz (1977a; 1977b) provided the framework that underlies subsequent computational linguistic research on the modeling of focusing of attention in discourse. This work established the context in which centering was formulated. It distinguished between two levels of fo-cusing: immediate (or local) and global. While global focusing \is determined by the total discourse and situational setting of an utterance and innuences : : : the overall interpretation of an utterance," immediate focus \refers to the innuence of a listener's memory for the linguistic form of an utterance (the actual words and the syntactic structure) on his interpretation of a subsequent utterance" (Grosz, 1977b), page 5]. Grosz (op. cit.) established two ideas fundamental to centering. First, immediate focus is a local level of processing in contrast to global focusing. It models utterance by utterance