The question of semantic underdetermination is related to the distinction between what is said and what is implicated. In this paper we examine the relevance-theoretic notion of enrichment as a procedure for developing what is said into a fully specified proposition or explicature. We make the claim that there are two forms of such a procedure, viz. grammatically-motivated and conceptually-motivated enrichment, and discuss their role in communication. We further contend that the notion of enrichment and the other procedures of propositional development recognized in the relevance-theoretic literature are insufficient to account for all cases of explicated meaning. In this connection, we propose other cognitive mechanisms such as mitigation and - more interestingly-metaphoric and metonymic mappings. This discussion allows us to cast some light on the implicature/explicature division line and to rank as explicatures some cases of inferences which have so far been considered as implicatures, including those where metaphor and metonymy are involved. Finally we examine the role of metaphoric and metonymic mappings -both in isolation and as part of conceptual interaction systems- in the production of explicatures, which allows us to understand better the communicative potential of these cognitive mechanisms.