Categorization and metaphor understanding.

Glucksberg and Keysar (1990) have proposed a class-inclusion model of metaphor comprehension. This theory suggests that metaphors are not understood as implicit similes but are seen as class-inclusion statements in which the topic of a metaphor is assigned to a diagnostic, ad hoc category, whereas the metaphor's vehicle is a prototypical member of that category. The author claims that verbal metaphors are not simply instantiations of temporary, ad hoc categories but reflect preexisting conceptual mappings in long-term memory that are metaphorically structured. Various evidence from cognitive linguistics, philosophy, and psychology are described in support of this claim. Evidence is also presented that supports, contrary to Glucksberg and Keysar's position, the role of tacit conceptual metaphors in the comprehension of verbal metaphors in discourse.