Metaphor is a rhetorical device used to compare two dissimilar objects or ideas in an implication that establishes an equivalency between the two. There are numerous types of metaphors. They are used in both classic rhetorical constructions and in everyday casual language. The degree of the comparison dictates what type of metaphor it is. Though there are more than a dozen distinct types of metaphors, there are five primary types: allegorical, absolute, mixed, extended, and dead metaphors.
Allegory is a metaphor that employs an extended story illustrating the comparison between two things using symbols rather than explicit words. An allegory in literature often presents the overt elements of a given story along with subtle, nuanced commentary for other events that the author wishes to show an equivalency with. For example, an element of the novel The Lion, The Witch and The Wardrobe is considered an allegory for the resurrection of Christ.
Absolute metaphor, compared with other types, cannot be obfuscated or reduced in any way. An absolute metaphor presents a simple equivalency, such as light standing for knowledge or snow indicating purity. Absolute metaphors can be symbolic or literal, and they differ from other types of metaphors in that they cannot be replaced by other metaphoric constructions.
Mixed metaphor is one of the most common types of metaphors, yet they may be difficult to understand. A mixed metaphor is the blending of two contradictory elements that are completely inconsistent in type, yet the symbolic meaning of the comparison is still conveyed. Sometimes the mixed metaphor can be employed intentionally for effect. For example, "There's no place like a home on the range" blends two well-known idioms.
Extended metaphor presents a complex comparison with multiple objects. It compares a primary object with a symbolic object, then compares secondary objects connected to the primary with other elements of the symbolic object. For example, Shakespeare's famous "All the world's a stage, And the men and women merely players" is an extended metaphor, in which the "world" and the "stage" act as the primary objects, while "we" and "players" represent the secondary objects.
Dead metaphor offers a comparison that is not symbolic in form, but to physical motion instead. A dead metaphor is simply a comparison that goes unnoticed because the metaphor rests on a comparison that has simply become part of the language. It often involves the use of an idiom. For example, the sentence "the committee will hold a meeting" is a dead metaphor with respect to the word hold. The committee cannot physically grasp the meeting, but the word is being used to equate a physical action with a conceptual one.