This report summarizes a research program in modeling human communication ability. The methodology involved selecting a single, naturally occurring dialogue, instructing a human observer to extract certain aspects relative to its comprehension, and then using these aspects to guide the construction and verification of the model. The model assumes a theory of language which states that people use language to pursue their own goals. Effective communication occurs in dialogues as the result of a common body of interrelated, cooperative goal structures. The report contains a detailed statement of the problem, a review of the state of related research, a description of the contributions of this research to linguistic theory, and a description of the research methodology. It then describes the model in its current state of development, discusses a detailed simulation, and explores the role of the observer in the research. (Author/WBC)