A semantic and pragmatic discussion of the following topics: discourse (for which some models are proposed), presupposition (it is argued that presuppositions are entailments and a notion of 'strength of presupposition' is introduced), conversational and conventional implicatures, negation (with respect to which it is claimed that negative sentences usually do not presuppose the presuppositions of their corresponding positive sentences), subordination, and the presuppositions of embedded sentences.