 Dynamic semantics is particularly suitable to describe how different types of linguistic material affect different aspects of the information state. In particular, dynamic semantics allows one to efficiently model the difference between at-issue content, e.g., the content that is asserted by the utterance of a declarative sentence and non-at issue content, content that plays some secondary role. For instance, the at-issue content of  (19)  is that John’s neighbor was arrested yesterday: it is the message the speaker intends to assert. The appositive who I have never met is not at issue. One way to see this is that an interlocutor can only respond to  (19)  with No! That’s not true! if s/he intends to challenge the fact that the neighbor was arrested, not if s/he merely wishes to express their disbelief in the speaker’s claim of never having met the neighbor.