This seminar aims at discussing a crucial issue for the semantics of natural language, that is, the issue of non-asserted meanings, although they are intentionally communicated and linguistically expressed. Traditionally, these meanings are defined as presuppositions, satisfying some criteria (resistance to interrogation, and negation for instance). Since the seminal work by Grice, another type of non-asserted meaning, called implicatures, has made the picture more complex. In this seminar, classical approaches and more recent ones will be discussed.