Dr. King's use of rhetoric to explain his dream

A famous speech that effectively uses the three forms of rhetorical appeals -- ethos, pathos and logos -- is Martin Luther King, Jr.'s "I Have a Dream."

The full transcript of the speech is available at:  http://www.archives.gov/press/exhibits/dream-speech.pdf.

Ethos
This is the "ethical appeal," but not in the exact sense of the modern definition. Instead, it relates to the accountability and credibility of the author or speaker. In King's "I Have a Dream" speech, he establishes himself as a reliable source.
Five score years ago a great American in whose symbolic shadow we stand today signed the Emancipation Proclamation. This momentous decree is a great beacon light of hope to millions of Negro slaves who had been seared in the flames of withering injustice.
Through this quote, the audience of the speech can conclude that Martin Luther King, Jr. is well-educated on the subject of African-American history and has a passionate, well-founded opinion on the topic based on facts and historical evidence. This can again be seen in later incidences where he utilizes quotes from the United States Constitution and other patriotic sayings and songs. But, King also continues:
And that is something that I must say to my people who stand on the worn threshold which leads into the palace of justice. In the process of gaining our rightful place we must not be guilty of wrongful deeds. Let us not seek to satisfy our thirst for freedom by drinking from the cup of bitterness and hatred.
We must forever conduct our struggle on the high plane of dignity and discipline. We must not allow our creative protests to degenerate into physical violence. Again and again we must rise to the majestic heights of meeting physical force with soul force.
This paragraph continues to reveal the extrinsic ethos of Dr. Martin Luther King, Jr. He establishes his character and morality, one who does not fight a wrong with a wrong. King promotes peaceful means, those permitted by the United States Constitution, to implement change in a society. His extrinsic ethos of character, education, expertise and experience are completely unveiled in his speech.

Further adding to his extrinsic ethos was his existing status in the African-American society at the time. Many people already trusted him, and he was already an established leader of the Civil Rights Movement. His title as a doctor further shows his reliability.

Finally, throughout his speech, he utilizes visual imagery, figurative language and correct use of English grammar, revealing his strong intrinsic ethos.

Martin Luther King, Jr.'s speech at the Lincoln Memorial in 1963.

Pathos
This is the pathetic appeal, or an attempt to appeal to the audience. King immediately uses pathos in the start of his speech:
I am happy to join with you today in what will go down in history as the greatest demonstration for freedom in the history of our nation.
King establishes himself as a friend and a peer who is assisting people who have been denied rights. He capitalizes on the audience's self-interest, as well as his own to present a sense of pride in what they are doing at the Lincoln Memorial.
In a sense we've come to our nation's capital to cash a check. When the architects of our Republic wrote the magnificent words of the Constitution and the Declaration of Independence, they were signing a promissory note to which every American was to fall heir. This note was a promise - yes, black men as well as white men - would be guaranteed the unalienable rights of life, liberty and the pursuit of happiness. It is obvious today that America has defaulted on this promissory note insofar as her citizens of color are concerned. Instead of honoring this sacred obligation, American has given the Negro people a bad check, a check which has come back marked 'insufficient funds.'
 But we refuse to believe that the bank of justice is bankrupt. We refuse to believe that there are insufficient funds in the great vaults of opportunity of this nation. So we've come to cash this check, a check that will give us upon demand the riches of freedom and the security of justice.
In addition to the great visual imagery used, King instills anger at injustice in the African-American community by creating an analogy of a broken promise and a plan of redemption in the above paragraph. It provokes the audience's emotions to rise up and fight for what is rightfully theirs.

But, perhaps the instance where King's strong pathos is shown most clearly is the paragraph that he and this speech are most famous for.
... Some of you have come fresh from narrow jail cells. Some of you have come from areas where your quest for freedom left you battered by the storms of persecution and staggered by the winds of police brutality... 
I say to you today, my friends, though, even though we face the difficulties of today and tomorrow, I still have a dream. It is a dream deeply rooted in the American dream. I have a dream that one day this nation will rise up, live out the true meaning of its creed: 'We hold these truths to be self-evident, that all men are created equal.'
His intentional use of "we" and the various groups that have struggled thus far paints a picture of a segment of society facing difficulties together, thereby appealing to most, if not all, of those gathered at the Lincoln Memorial that day in 1963. It not only shows a struggle, but also a potential for an optimistic outcome, only if this group of African-Americans and Americans united to fight what was unjust. King also utilizes the American dream and Constitution, both which invoke a great sense of pride and unity to those living in the United States. The reminder of the denial of both to many of those gathered at the Lincoln Memorial during the speech serves as a common ground for everyone there.

The phrase "my friends" poses King as a peer and one that will accompany them on the long road ahead to equality, allowing those listening to his speech to trust him and have confidence in following his plan to gain justice.

In closing his speech, King says:
When we allow freedom to ring - when we let it ring from every city and every hamlet, from every state and every city, we will be able to speed up that day when all of God's children, black men and white men, Jews and Gentiles, Protestants and Catholics, will be able to join hands...
More than anything, this paragraph shows King as a friend to all and appeals to the general public, regardless of their background. King shows that the journey he is embarking on will create a better world where every group of people is treated equally.

Dr. King in front of the Lincoln Memorial.
Courtesy: http://www.kentcountyartscouncil.org/wp-content/uploads/2013/08/MLKJ-march-on-washington2.jpg

Logos
Finally, logos is the logical appeal and relates to the speaker's attempt to use logic. King justifies all that he says and successfully uses logos in this speech.

King supports generalizations about discrimination and segregation using specific examples.
We cannot walk alone. And as we walk we must make the pledge that we shall always march ahead. We cannot turn back. There are those who are asking the devotees of civil rights, 'When will you be satisfied?' We can never be satisfied as long as the Negro is the victim of the unspeakable horrors of police brutality.
We can never be satisfied as long as our bodies, heavy with the fatigue of travel, cannot gain lodging in the motels of the highways and the hotels of the city.
We cannot be satisfied as the Negro's basic mobility is from a smaller ghetto to a larger one. We can never be satisfied as long as our children are stripped of their adulthood and robbed of their dignity by signs stating 'For Whites Only.'
We cannot be satisfied as long as the Negro in Mississippi cannot vote and the Negro in New York believes he has nothing for which to vote.
King highlights denied rights of African-Americans that the American Constitution supposedly guaranteed for every person, regardless of their background. He also establishes the demands that must be met, made up of demands that logically come from the list of "inalienable rights."

Dr. Martin Luther King, Jr. is famous for the work he did in helping ignite and advance the Civil Rights Movement. Perhaps the reason he was so successful is because of his ability to combine ethos, pathos and logos whenever he spoke or wrote.