I've written elsewhere about how and why rhetoric works so effectively in getting your message across (see How (and why) rhetoric works on the brain) by momentarily switching your brain into 'slow-thinking' mode (see Fast vs slow thinking). But I read an artcle recently which throws further light on the subject. The link to the full article is at the bottom of this page, but as it's a bit wordy, lengthy and scientific, I thought I'd give you my take on how it relates to rhetoric.
It points out that all music, all over the world, uses repetition as a major theme. Hit songs in the US or UK charts, for example, invariably have a catchy chorus that is repeated several times at intervals. Plus, we tend to listen to our favorite tracks again and again and again rather than seeking variety. The musicologist David Huron at Ohio State University estimates that during more than 90 per cent of the time spent listening to music, people are actually hearing passages that they've listened to before.
In one experiment by Diana Deutsch of UC San Diego, a sentence is spoken, and then one part of it repeated again and again (in spoken tones). If you then listen to the full sentence again, the repeated section 'leaps out' at you as if they're being sung. The very act of repetition has somehow 'musicalized' the words. It's amazing. The sound files are in the full article, I suggest you take 30 seconds to listen to them.
And when words are 'musicalized' int his way via repetition, our focus and attention shifts from the meaning of the words to the patterns of high and low pitchesand the rhythm of the speech. It even invites you to hum or tap along with it. In effect, when words have been 'musicalized' in this way, we cease to simply listen to them; we somehow participate in what's being said.
In fact the emotional regions of our brains are activated far more by music we've heard before, even if it's not to our taste. This is why something we hate but we've heard again and again can get stuck in our brains so that we can't stop mentally replaying it (the Germans have a great word for when this happens; they call it an ohrwurm, or 'earworm').
This is why we set something to music when we're trying to memorize it, such as the alphabet or multiplication tables, or a list of the Presidents of the US. In anutshell, if we can somehow 'musicalize' a phrase or point, it becomes more memorable.
What has this got to do with using rhetoric in presentations to get your message across? Simply this: some of the most powerful and commonly used rhetorical techniques involve repetition.
Anaphora repeats the same word or words at the beginning of successive sentences or phrases, e.g.
"We shall fight in France, we shall fight on the seas and oceans, we shall fight with growing confidence and growing strength in the air, we shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills, we shall never surrender" - Sir Winston Churchill
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 state sweltering with the heat of injustice, sweltering with the heat of oppression, will be transformed into an oasis of freedom and justice" - Martin Luther King
Antistrophe repeats them at the end of successive sentences, e.g.
"Government of the people, by the people, for the people" - Abraham Lincoln
"I say to them tonight, there's not a liberal America and a conservative America, there's the United States of America.There's not a black America and white America and Latino America and Asian America; there's the United States of America" - President Obama
Mesodiplosis does it in the middle of successive sentences, e.g.
"American leadership depends on a military so strong that no one would think to engage it. Our military strength depends on an economy so strong that it can support such a military. And our economy depends on a people so strong, so educated, so resolute, so hard working, so inventive, and so devoted to their children's future, that other nations look at us with respect and admiration" - Mitt Romney
Symploce does it at the beginning and end, e.g.
"Much of what I say might sound bitter, but it's the truth . Much of what I say might sound like it's stirring up trouble, but it's the truth. Much of what I say might sound like it's hate, but it's the truth" - Malcolm X
The reason these all work in making your words both impactful and memorable is that a phrase that sounds arbitrary the first time comes to sound purposefully shaped and communicative and meaningful the second or third.
Tthe full article is: "One more time: why do we listen to our favourite music over and over again? Because repeated sounds work magic in our brains" by Elizabeth Hellmuth Margulis