Traditional thinking on metaphors has divided them into two camps: dead and alive. Conventional expressions from everyday language are classified as dead, while much rarer novel or poetic metaphors are alive. In the 1980s, new theories on the cognitive processes involved with the use of metaphor challenged these assumptions, but with little empirical support. Drawing on the latest research in linguistics, semiotics, philosophy, and psychology, Cornelia Muller here unveils a new approach that refutes the rigid dead/alive dichotomy, offering in its place a more dynamic model: sleeping and waking.To build this model, Muller presents an overview of notions of metaphor from the classical period to the present; studies in detail how metaphors function in speech, text, gesture, and images; and examines the way mixed metaphors sometimes make sense and sometimes do not. This analysis leads her to conclude that metaphors may oscillate between various degrees of sleeping and waking as their status changes depending on context and intention.