Gentner and Bowdle argue in their chapter that metaphors and similes are understood with processes of similarity and analogy ("Metaphor as Structure-Mapping"). They describe how processes of structural alignment, inference projection, progressive abstraction, and re-representation of different domains are critical to immediate processing of both metaphors and similes. Moreover, widespread conceptual metaphors may be best characterized as extended structure-mappings between domains. Gentner and Bowdle then present their "career of metaphor" theory which claims that metaphors and similes typically evolve from being understood as novel comparison statements to being interpreted as category-inclusion statements in which the vehicle terms serve as the best instances of ad hoc categories. The "career of metaphor" hypothesis aims to offer a unified framework for understanding metaphor, analogy, and similarity. (Raymond Gibbs)