A metaphor is a figure of speech that expresses an idea through a comparison between two objects or ideas. In Art and Illusion, Gombrich uses language as a metaphor for art. That is, he suggests that artists develop a "vocabulary" of artistic schemata that allow them to build their images. But the schemata available in any historic period can constitute a limitation within which artists tend to work. He likens the schemata to a writer's vocabulary that both builds and limits the work the writer creates. Indeed, through his use of the words "language of representation," "reading," "grammar," and "articulation," for example, Gombrich further builds the metaphor that art and language are comparable forms of human communication and representation.