figure of speech that implies comparison between two unlike entities, as distinguished from simile, an explicit comparison signalled by the words “like” or “as.”

The distinction is not simple. The metaphor makes a qualitative leap from a reasonable, perhaps prosaic comparison, to an identification or fusion of two objects, to make one new entity partaking of the characteristics of both. Many critics regard the making of metaphors as a system of thought antedating or bypassing logic.

Metaphor is the fundamental language of poetry, although it is common on all levels and in all kinds of language. Many words were originally vivid images, although they exist now as dead metaphors whose original aptness has been lost—for example, “daisy” (day's eye). Other words, such as “nightfall,” are dormant images. In addition to single words, everyday language abounds in phrases and expressions that once were metaphors. “Time flies” is an ancient metaphorical expression. When a poet says “The Bird of Time has but a little way / To flutter—and the Bird is on the Wing” (The Rubáiyát of Omar Khayyam), he is constructing a new metaphor on the foundations of an older, stock metaphor. When Tennessee Williams entitles his play Sweet Bird of Youth, he, too, is referring to that Bird of Time that flies. Thus, metaphorical language develops continuously in complexity just as ordinary language does.

In poetry a metaphor may perform varied functions from the mere noting of a likeness to the evocation of a swarm of associations; it may exist as a minor beauty or it may be the central concept and controlling image of the poem. The familiar metaphor “Iron Horse,” for train, for example, becomes the elaborate central concept of one of Emily Dickinson's poems, which begins

A mixed metaphor is the linking of two or more disparate elements, which often results in an unintentionally comic effect produced by the writer's insensitivity to the literal meaning of words or by the falseness of the comparison. A mixed metaphor may also be used with great effectiveness, however, as in Hamlet's (Hamlet)

in which “sea” should be replaced by “host” for the strictly correct completion of the metaphor.