A mixed metaphor is a type of metaphor in which the metaphoric image includes either two different metaphors together, which do not function well together, or several concepts that ultimately make the metaphor confusing. Such metaphors are usually considered poor or inappropriate, especially since they can ultimately result in a lack of meaning and render the intended imagery or concept pointless for a reader or listener. A mixed metaphor usually results from too many ideas being used together — “her eyes were stars floating on a soft breeze” — or from a single metaphor being extended out in a way that ultimately corrupts the image — “that man is a dog, slithering about and hissing.”
The basic structure of a mixed metaphor is much like any other type of metaphor, except the images and ideas used together do not quite function well. A metaphor is simply a literary or rhetorical device in which two objects are directly compared to each other, often to make an unknown object more relatable through comparison to a known object. Some simple metaphors include “he is a dog” or “my heart is a caged bird.”
One of the powerful things about metaphors is that, when well constructed, they may be expanded and used throughout a longer image to reinforce numerous ideas. “He is a dog,” for example, can be followed by “always chasing cars” or “loyal to a fault” and express different ideas in a fairly complex way. Similarly, the metaphor “my heart is a caged bird” could be extended further by “beating against its bars and singing to be free,” which continues the image of a bird and expresses longing.
If metaphors are not extended properly, however, an expression can turn into a mixed metaphor in which meaning is obfuscated by the language used. This usually occurs due to either too many images being used together or language chosen that does not truly reinforce the initial metaphor. A mixed metaphor could occur from “my heart is a caged bird” by continuing it with “calling each morning to the rising sun.” While this does extend the bird image of the metaphor, it seems to indicate a rooster, which is not usually associated with a bird in a cage but with a free or barnyard bird.
Many times, a mixed metaphor occurs due to the imagery in the metaphor being extended with language that does not support the initial metaphor. “He slithered through the room,” seems to indicate that a man is acting like a snake, using the man and snake to create the initial metaphor. If this metaphor is extended as “He slithered through the room, panting and cat-calling as he went,” then the metaphor falls apart. The initial image of a man and snake is strong, but the introduction of ideas associated with dogs and cats turns it into a mixed metaphor and simply becomes confusing.