 Unlike Kaplan, Stalnaker has a homogeneous theory of contexts and contents. Both context and content can be conceived of as propositions, or equivalently as sets of worlds. A context is a set of worlds, that capture the common ground in a conversation, the presuppositions that all of the participants share. The point of an assertion is to change the common ground. An utterance token is associated with a propositional concept, which characterizes the context-change potential of an assertion.