Metaphor, a common figure of speech, is a comparison of one thing with another: happiness is a sunny day, loneliness is a locked door, coziness is a cat on your lap.

This is probably one of Martin Luther King's favorite rhetorical devices. There's a metaphor in every section, and nearly every paragraph, of "I Have a Dream."

He kicks off the speech with a metaphor, describing the Emancipation Proclamation as a "light of hope to millions of Negro slaves" (2.2). He continues in the same sentence by describing slavery as "[searing] in the flames of withering injustice" (2.2). The end of slavery was a "joyous daybreak" (2.2).

The point of metaphor is to compare unlike things. A historical document is not literally a light—because that would be a) hard to read and b) too hot to handle—but it is figuratively one.

The "I have a dream" section of the speech also uses metaphors. In fact, the idea of a "dream" as a representation of historical progress is a metaphor in and of itself. Meanwhile, there are little ones dropped in there. Discrimination in Mississippi is "the heat of oppression" (14.1). Across America, racism is "jangling" (18.4), a word that is reminiscent of clanking jail keys.

By the way, the combination of multiple metaphors one after the other is sometimes called "mixing metaphors" In writing, its not always the best move…but in speeches it can often sound pretty cool.

You get the idea? MLK's army of metaphors here makes the speech sound grandiloquent, and not in a bad way. Most folks dig a solid metaphor, especially when delivered by a fiery and super-skilled speaker.