TOWARD A COMPUTATIONAL THEORY OF PRAGMATICS--DISCOURSE, PRESUPPOSITION, AND IMPLICATURE

This dissertation is a computational attempt to treat certain aspects of pragmatics of natural language based on a logical language augmentated by computational elements.;Another extension is the concept of hierarchically organized universes of discourse, which will appropriately store the information acquired during the processing of a discourse. The hierarchical organization provides a way of making meaningful distinctions among various pieces of information in the system and offers a natural treatment of the phenomena of anaphora, as well as the treatment of quantifiers.;This dissertation focuses on the treatment of "implicatures." Since this term has been used in various senses, a feature notation, based on Grice's intention to make a distinction between 'what is said' and 'what is implicated', is introduced to provide both an adequate taxonomy and a precise definition of "implicatures," including but not limited to what has been called "presuppositions.".;Based on the feature notation for implicatures, new kinds of procedures are introduced for pragmatic aspects of language. The usual semantic procedures are responsible for computing the compositional semantics, while additional pragmatic procedures perform cumulative pragmatic computations. The pragmatic procedures cause changes to the universes of discourse, which are carried over to later stages of interpretation as new information. This cumulative nature of the pragmatic procedures is in sharp contrast to the compositional nature of the semantic procedures.;One of the computational features introduced is the concept of super-interpretation in addition to the ordinary interpretation of language which is performed compositionally in the sense of Frege. In dealing with pragmatic aspects of natural language, however, compositionality does not always provide all the desired results of the language use. Super-interpretation is added to complement the interpretation as a post-compositional element in the computational interpretation system.;This dissertation shows how the integration of the compositional and the cumulative behaviors of information processing contributes to the treatment of the semantics and the pragmatics of natural language. The indispensability of this kind of integration in a unified system is demonstrated by comparing the current system with other existing well-defined formal frameworks, particularly works by Karttunen and Peters and by Gazdar.