I’ve been thinking about Martin Luther King as a speaker again recently, because of the holiday, of course, but also because of the release of the movie Selma. And for one other reason: I often use King as an example of a great speaker when I’m working one-on-one with executives and professional speakers.

No surprise there; King is one of the giants of the last century. What is surprising, perhaps, is that while the discussion often centers on his magnificent voice, its passion and authority, and his captivating use of the pause – all of his vocal techniques, in other words, honed in years of preaching – my clients often don’t think about King’s rhetorical expertise until I point it out to them.

King uses two main techniques, (appropriate) repetition and the rule of threes, to convey emotion through his rhetoric. And while everyone has noticed the first one – it’s how the speech is known – few have remarked on the second. But this less-recognized rhetorical technique is the one, I believe, that makes the speech resonate so powerfully with audiences from its first delivery at the Washington Mall on August 23, 1963, to today.

First let’s look at the use of repetition to create passion:

I say to you today, my friends, that in spite of the difficulties and frustrations of the moment 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 and live out the true meaning of its creed: “We hold these truths to be self – evident; that all men are created equal.”

I have a dream that one day on the red hills of Georgia the sons of former slaves and the sons of former slave owners will be able to sit down together at the table of brotherhood.

I have a dream that one day even the state of Mississippi, a desert state sweltering in the heat of injustice and oppression, will be transformed into an oasis of freedom and justice.

I have a dream that my four little 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.

I have a dream today.

I have a dream that one day the state of Alabama, whose governor’s lips are presently dripping with the words of interposition and nullification, will be transformed into a situation where little black boys and black girls will be able to join hands with little white boys and white girls and walk together as sisters and brothers.

I have a dream today.

There’s a real art to repetition. How do you manage it so that it doesn’t sound simple – minded but rather, as in this case, creates a crescendo of emotion that builds with each reaffirmation of the phrase, “I have a dream”?

The key is the phrase that’s repeated. It has to be able to bear the weight, and the words have to be affirmative, simple, and evocative. In King’s case, the words were perfect. But it’s not easy to find the right ones. The political world is full of repetitive phrasing and chanting of key phrases that the speaker begins and the audience takes over, but most of them are quickly forgotten.

And King repeats the phrase in different ways in his sentences, sometimes at the beginning of a longer sentence and sometimes essentially standing on its own, creating further interest and tension.

Then there’s the Rule of Three. The rule of three plays magnificently at the end of the speech, when King invokes a spiritual and brings the audience to its feet:

When we let freedom ring, when we let it ring from every village 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 and sing in the words of the old Negro spiritual, “Free at last! Free at last! Thank God Almighty, we are free at last!”

There are actually two sets of threes here: the groupings of black and white, Jews and Gentiles, and Protestants and Catholics, as well as the final triumphant, “Free at last!”

And there are further subtleties. By giving us two groups of two — every village and every hamlet and every state and every city — King creates in us a need to have the completion of a group of three. And of course he balances the two sets of groups perfectly. It’s an amazing performance.

Perhaps you’re thinking, Well, that was easy for Reverend King. He was a great speaker and had time to prepare. But how can I achieve that kind of rhetorical passion in my communications, which are mostly off the cuff?

You may be astonished to find out that the second half of King’s speech, where these quotes come from, was ad-libbed.

What is it about groups of three that heighten emotion and create passion? Why do we respond so powerfully to them? It’s a mystery — something psychological. Some say it has to do with religious symbolism, since there are groups of three in most major religions, but that may be putting the cart before the horse: the religions may have settled on groups of threes for the same psychological reasons that everyone else finds them powerful.

Whatever the reason, we find something complete and satisfying in a group of three, like a three-legged stool that can stand firmly on uneven ground. And so you should use them in your communications – as well as repetition – when you’re striving to convey passion.