Proceedings of the Annual Meeting of the Cognitive Science Society

Two experiments assessed the membership functions that Germ an speakers assign to 12 adverb phrases and 17 modal verb fonns that express probability assessments. These expressions fall largely into three rather homogeneous classes. The membership functions are used as part of the semantic knowledge base of the natural language dialog system Pragma, one of whose purposes is to model pragmatic and contextual influences on the use of vague expressions. The system's normative model accounts for the role, in the selection and interpretation of vague probability expressions, of the listener's prior expectations, the speaker's dialog motivation, and the expressions that the speaker could have used but did not.