This thesis defends Semantic Pluralism, the view that sentences express sets of propositions in context. It puts forward two arguments against Contextualism, the main opposing view, on which each sentence expresses exactly one proposition in context. It spells out two versions of Pluralism: Flexible Pluralism, which takes most sentences to be context-sensitive, and Strong Pluralism, which denies that context-sensitivity is widespread. And it defends Flexible Pluralism and Strong Pluralism from a number of objections.