Ethos is a rhetorical strategy where the speaker relies on credibility and trust to solidify a position or argument. This approach increases the authority and believability of the speaker and therefore of the argument itself.

The "I Have a Dream" speech is an excellent example of various rhetorical strategies. One example of ethos appears in the second sentence:

Five score years ago a great American in whose symbolic shadow we stand today signed the Emancipation Proclamation.

King opens by asking Americans to recall the words of another "great American" who pushed for social change: Abraham Lincoln. This immediately brings a sense of authority to his speech. Lincoln's work and words in the Emancipation Proclamation provide a context for King's first main point—the vision of Lincoln has not become a reality for Black Americans. Lincoln is considered a powerfully significant American president, and King invokes the sense of authority associated with him to establish credibility.

He again turns to ethos just a few lines later:

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.

The Constitution and Declaration of Independence are two foundational American documents, and they invoke a sense of legal authority. By including this reference, King reminds listeners that these texts were written for all people. This furthers King's credibility and authority by aligning his own vision with the original vision of the nation's founders.