The way in which we understand the concept of intelligence is rooted in metaphor and metonymy; for example, it is common to describe people as bright or thick or call them silly asses. This book explores the motivation for some of the lexemes in this semantic field across the history of the English language, considering the range of cognitive mechanisms and cultural factors that can inform metaphorical and metonymical mappings. It focuses on data from the Historical Thesaurus of English, and considers three of the concepts that have been important in the way intelligence is conceptualised diachronically: the senses, density, and animals. A detailed case study of these source concepts provides a starting point for a wider discussion about the nature of mapping processes, and Allan argues that a diachronic approach offers a fresh perspective which can both complement and challenge current theories of metaphor and metonymy.