Presupposition and expressive meaning

Presuppositions are well known phenomena. One way of treating them is as partial 'meaning-functions'. There is an attractive argument that holds that in order to explain the contrast between such sentences as "John came into the room" and "That bastard John came into the room" it is required to make our semantic theory essentially more complex. This argument appeals to the fact that contrasts such as the ones just mentioned play a role in the validity of logical inferences. In this paper I argue that these contrasts can be accounted for by appealing to presuppositions. In order to defend this view we will have to offer a characterization of logical consequence that applies to sentences that involve presuppositions.