The central aim of this study is to elucidate the nature of the semantics / pragmatics distinction in both synchrony and diachrony. The author proposes a definition of semantics and pragmatics that is orthogonal to the question of truth-conditionality, and discusses the status of various types of meaning with respect to this definition. A corollary aim of the study is to propose an account of how and why erstwhile pragmatically-determined elements of meaning may, in the course of time, become semanticized. The nature, paths, and mechanisms of diachronic sense changes of the relevant type, as well as the motivations for them, are discussed in some detail. The author combines insights from different sources, prominently frame-based semantics, historical pragmatics, and Peircean semiotics, to arrive at a model of linguistic meaning that is both synchronically and diachronically dynamic, hence capable of integrating structure and usage. As a case study, the synchronic uses and diachronic evolution of the exceptionally polyfunctional French phasal adverbs deja ('already'), encore ('still/yet'), toujours ('still'), and enfin ('finally') are analyzed in some detail, with particular attention being paid to the semantic vs pragmatic nature of the various uses of these items. The book will be of interest to lexical semanticists, pragmaticians, historical linguists, functional/cognitive linguists, discourse analysts, and semioticians.