Martin Luther King Jr. was a superb orator, and he knew exactly how to apply rhetorical techniques to touch his audience's mind, heart, and spirit. Let's look at some of the rhetorical elements in King's famous “I Have a Dream” speech.
First, notice all the repetition in this speech. “I have a dream,” or a close variant of it, is repeated nine times, and most times, King follows up with an element of that dream—for instance, that his children will “one day live in a nation where they will not be judged by the color of their skin but by the content of their character” (he employs antithesis here, too, by contrasting color and content and skin and character in a fine example of parallelism). King also uses other instances of repetition to heighten his audience's excitement. At the end of the speech, for example, he repeats, “Let freedom ring” nine times.
Second, King makes wide use of allusions and quotations. He speaks of what his audience knows and holds in familiarity. He quotes the Bible and the Gettysburg Address and alludes to the Declaration of Independence, the US Constitution, and the Emancipation Proclamation. All of these sources give weight and credibility to his argument.
Third, King directly addresses his audience, inviting them to work together for true freedom. “Let us not wallow in the valley of despair,” he says, but rather live in hope.
Fourth, King employs several metaphors to add vividness to his speech. He speaks of America defaulting on the “promissory note” it has given to Black people. Instead, it has provided a “bad check” with “insufficient funds” to cover it. America promised freedom and equality but has not followed through.
Fifth, King adds color, interest, and rhythm to his speech through alliteration (the repetition of initial sounds) when he speaks of “trials and tribulations” and announces that it is time to “rise from the dark and desolate valley of segregation to the sunlit path of racial justice” (notice the metaphor here, too).
Indeed, King is a master of rhetoric, and he uses its techniques to enhance his message and make it more powerful to his audience.