This book offers a distinct approach to the analysis of the multiple meanings of English modals, conjunctions, conditionals and perception verbs. Although such ambiguities cannot easily be accounted for by feature-analyses of word meaning, Eve Sweetser's argument shows that they can be analysed both readily and systematically. Meaning relationships in general cannot be understood independently of human cognitive structure, including the metaphorical and cultural aspects of that structure. Sweetser shows that both lexical polysemy and pragmatic ambiguity are shaped by our metaphorical folk understanding of epistemic processes and of speech interaction. Similar regularities can be shown to structure the contrast between root, epistemic and 'speech-act' uses of modal verbs, multiple uses of conjunctions and conditionals, and certain processes of historical change observed in Indo-European languages. Since polysemy is typically the intermediate step in semantic change, the same regularities observable in polysemy can be extended to an analysis of semantic change. This book will attract students and researchers in linguistics, philosophy, the cognitive sciences, and all those interested in metaphor.