A metaphor is a figure of speech that makes a comparison between two unlike things, without using the word like or as. Metaphors assert the identity of dissimilar things, as when Macbeth asserts that life is a "brief candle." Metaphors can be subtle and powerful, and can transform people, places, objects, and ideas into whatever the writer imagines them to be.

An implied metaphor is a more subtle comparison; the terms being compared are not so specifically explained. For example, to describe a stubborn man unwilling to leave, one could say that he was "a mule standing his ground." This is a fairly explicit metaphor; the man is being compared to a mule. But to say that the man "brayed his refusal to leave" is to create an implied metaphor, because the subject (the man) is never overtly identified as a mule. Braying is associated with the mule, a notoriously stubborn creature, and so the comparison between the stubborn man and the mule is sustained. Implied metaphors can slip by inattentive readers who are not sensitive to such carefully chosen, highly concentrated language.

An extended metaphor is a sustained comparison in which part or all of a poem consists of a series of related metaphors. Robert Francis’s poem "Catch" relies on an extended metaphor that compares poetry to playing catch. A controlling metaphor runs through an entire work and determines the form or nature of that work. The controlling metaphor in Anne Bradstreet’s poem "The Author to Her Book" likens her book to a child. Synecdoche is a kind of metaphor in which a part of something is used to signify the whole, as when a gossip is called a "wagging tongue," or when ten ships are called "ten sails." Sometimes, synecdoche refers to the whole being used to signify the part, as in the phrase "Boston won the baseball game." Clearly, the entire city of Boston did not participate in the game; the whole of Boston is being used to signify the individuals who played and won the game.

Metonymy is a type of metaphor in which something closely associated with a subject is substituted for it. In this way, we speak of the "silver screen" to mean motion pictures, "the crown" to stand for the king, "the White House" to stand for the activities of the president. See also figures of speech, personification, simile.