Contrast and Contrastive Topic

The starting point of this paper is the observation that in a question-answer dialog the use of but instead of and is obligatory if the answer is overinformative in that it includes an additional topic. A focus-semantic analysis of but is presented showing that (a) but is focus-sensitive and (b) but requires a denial with respect to the appropriate quaestio. This analysis provides a uniform basis for explaining the different uses, e.g. semantic opposition, denial-of-expectation, and the topic change use of but. Beyond that it gives some insight into the interaction between information structure and discourse relations in constructing the discourse.