In this paper I explore the semantic import of contrast as a category of information structure. It has often been noticed that contrast is associated with specific grammatical correlates and has an impact on sentence structure in different languages. However, it is still not clear how the semantic contribution of contrast differs from the one of focus, since both categories have the function of evoking alternatives in discourse. As a consequence, it has been wondered whether in modeling information structure these two notions should be distinguished or reduced to each other. This contribution aims to show that focus and contrast have two different functions. It will be conservative in arguing that both are involved in the process of alternative generation. However, it will be shown that these alternatives are generated in two different sentential domains. In particular, contrast evokes alternatives within the background of the sentence. This hypothesis builds on the structured meaning approach of sentence structure. Moreover, the proposal assumes the discourse model elaborated in Farkas and Bruce (2010), which will allow us to ascribe a uniform semantic representation to assertions and polar questions and to account for pragmatic effects triggered by contrastive interpretations.