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Tens of thousands of words have been written about how the use of rhetoric can make a message persuasive, impactful and memorable. How it can burn it into your audience's brains. How it can make it stand out from the thousands of others competing for their attention. But far less (in fact hardly anything) has been written about why it's so effective. Why it has that impact on the brain. In effect, why it works.

I believe it's because it very briefly switches your audience's brains from autopilot - which if you think about it is how we listen to most presentations, just drifting along, letting the words wash over us - to what Daniel Kahneman calls 'slow thinking' (ST). At this point, if you haven't already read it, I'd recommend having a look at my article Fast- vs Slow-Thinking).

Summarizing that article in a couple of sentences, 'Fast Thinking' (FT) is what we use 90% of the time to complete day-today tasks. It’s done (ironically) without thinking, requires no conscious effort and is what we use when we’re doing several things at once.

We use ST the remaining 10% of the time, for tasks that require more mental effort and when we have to concentrate on something to the exclusion of other things.

ST a far more powerful process, but the reason we only use this thinking mode 10% of the time and not all of the time is that it takes up far more energy. Although our brains account for about 2% of our body weight, they consume about 20% of our energy (compared to about 8% in other primates), which is a massive amount. A chess grand master can lose up to 7lb in weight over the course of a chess tournament lasting 3-4 days. Just by using ST!

Einstein, Sir Isaac Newton and Plato were capable of using ST longer than the average Joe, but most people are only physically capable of engaging in it for a relatively short period of time. So 90% of the time you want to make your presentation as simple and easy to follow as possible. Unless .... you want the audience to concentrate on something for a short period of time. Then you should deliberately switch their brains over to ST. Which is where rhetoric comes in.

As far as I'm aware, no specific research has been done on how the brain reacts to rhetoric (e.g. putting people in a brain scanner and mapping what areas of the brain light up when they listen to 'I have a dream'), but we can learn a lot from how it reacts to poetry or great literature. One study at Liverpool University in the UK looked at what happened to people’s brain activity when they were exposed to some of Shakespeare’s ‘tricks.’

Shakespeare used 17,667 words, of which we think he invented 1,700 (if he didn’t invent them, his was the first recorded use of them). That’s 10%. He did this in several ways; through ‘functional shifts’ (i.e. changing the part of speech of words such as using a noun or a adjective as a verb as in ‘he thick my blood’ or ‘he childed as I fathered’), adding prefixes and suffixes, connecting words together, or just inventing them, the way some rappers do today.

So even for the people who watched his plays performed live in the early seventeenth century, they weren’t the easiest things to understand. Imagine watching a movie where you’ve never heard 10% of the words in the script before. You’d get the gist of what was happening, but it would take concentration. And the scientific study showed that’s exactly what happens.

The researchers at Liverpool University didn’t ‘overload’ their subjects’ brains with full sentences of ‘undiluted’ Shakespeare because it would have been too much; so many areas of the brain would have lit up that it would have been impossible to diagnose just what was causing what.  So they examined just the effect of the 'functional shifts', taking the words Shakespeare introduced/invented but surrounding them with ordinary, everyday language.

With each functional shift sentence (A) they also showed three other sentences – B: a ‘conventional’ one which made grammatical sense, and acted as a control; C: one which was grammatically correct but didn’t make sense; and D: one which was both grammatically wrong and also made no sense. So as an example:

A) The pizza was too hot to mouth.
B) The pizza was too hot to eat.
C) The pizza was too hot to sing.
D) The pizza was too hot to elephant.

So what happened? Well when the brain picked up something that didn’t seem to make sense, as in sentences C and D, the brain scanning equipment registered what neuroscientists call an N400 effect (if you’re interested, that’s a negative wave modulation 400 milliseconds after the onset of the critical word). The weirder the word, the larger the wave (i.e. ‘elephant’ caused a larger one than ‘sing’ – at least ’sing’ is a verb and therefore could logically follow the word ‘to’).

Effect of rhetoric on brain

But when the brain sensed a violation of grammar, as in A, the functional shift sentence(i.e. it understood what was being said, but knew something wasn't quite right), something different happened -   a different type of wave. A positive one peaking about 600 milliseconds after the word, called a P600.

The effect of a P600 is to prime the brain to look out for more difficulty and work at a higher level. In other words, it triggers a move to ST, which raises attention, gives more weight to the sentence as a whole, and makes it more memorable. Experts believe it’s this enhanced brain activity which makes Shakespeare so memorable.

So the lesson learned is that when we encounter words put together in an unusual or exciting or different way, our brains briefly switch to using ST. Maybe more than briefly. How many times have you read a fantastically crafted sentence and thought, “Wow! What a great way of putting that point!” and then stopped, gone back and re-read it, perhaps several times, to really let it sink into your brain?

Stephen Fry (an English polymath who’s an actor, screenwriter, author, playwright, journalist, poet, comedian, television presenter, film director and all-round clever clogs) once said that the first time he realized words could be used for more than just communicating basic information, e.g. ‘pass the salt’ was when at the age of 10 he saw a film of Oscar Wilde’s ‘The Importance of Being Earnest’, and heard the line "Would you be in any way offended if I said that you seem to me to be the visible personification of absolute perfection?"

He literally stopped dead, thinking it the most beautiful thing he’d ever heard.  He repeated the words to himself over and over and said when he did so, ‘it was like my mouth dancing.’ Who among us hasn’t done something similar?The probability is that his brain experienced a P600. He recognized and understood each of the words in the sentence, but had never seen them put together in that particular way.

Let’s take one line of Shakespeare at random: "The evil that men do lives after them / the good if oft interred with their bones". Would the point have been made more memorably if he’d written it far more plainly, e.g. “Men are often remembered more for the bad things they do than for the good.” I think not. Once you’ve read his version, it’s virtually impossible to think of a better way of saying it.

BUT ….. the first time you heard or read it, you may have had to stop for a second and use ST to take it in. Which is why, of course, it’s so effective.

Professor Philip Davis, one of the authors of the research, says:

"The brain reacts … in a similar way to putting a jigsaw puzzle together. If it is easy to see which pieces slot together you become bored of the game, but if the pieces don't appear to fit, when we know they should, the brain becomes excited….. Shakespeare surprises the brain and catches it off guard in a manner that produces a sudden burst of activity - a sense of drama created out of the simplest of things."

His colleague Professor Neil Watson says:

"The effect on the brain is a bit like a magic trick; we know what the trick means but not how it happened. Instead of being confused by this in a negative sense, the brain is positively excited. The brain signature is relatively uneventful when we (easily) understand the meaning of a word (or sentence) but when the word (or sentence is unusual) brain readings suddenly peak. The brain is then forced to retrace its thinking process in order to understand what it is supposed to make of it."

While a typical rhetorical device in isolation wouldn’t have as big an effect as a piece of Shakespearean prose, it would have a similar effect, as many of them ‘play’ with the rules of grammar. Let’s take  Abraham Lincoln’s famous words, “But in a larger sense, we cannot dedicate, we cannot consecrate, we cannot hallow this ground” This, as you’ll discover in other articles, uses three devices – Anaphora, Asyndeton and a Tricolon.

Now if Lincoln’s school teacher had been present at the Gettysburg Address, she’d probably have rapped his knuckles upon hearing this and said something to the effect of, “Abe – the use of ‘we cannot’ three times is superfluous and you’ve omitted the conjunction ‘or’. The grammatically correct English is ‘We cannot dedicate, consecrate or hallow this ground’.” And from a purely grammatical viewpoint, of course, she’d have been right.

A second example would be Winston Churchill’s ‘Fight them on the beaches’ speech. The grammatically correct version of what he eventually said would have been:

“We shall fight in France, on the seas and oceans, with growing confidence and growing strength in the air, on the beaches, on the landing grounds, in the fields and in the streets, in the hills... and we will never surrender.”

And those words would probably have been forgotten, lost amongst the millions that he uttered in formal speeches over his long a distinguished career. But he asked himself, ‘What’s the point I’m trying to make here?’ And that point (he had four audiences: the British public, the Empire, Hitler and the USA) was that Great Britain  - despite being isolated because Germany had overrun virtually all of Europe – wasn’t going to surrender. It was going to fight.

That was the point he wanted to emphasize. So in line with his own advice - “If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack”  - he said the following instead, using Anaphora:

“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.”

And instead of being lost among millions of others, those words became some of the most memorable he ever uttered (“We’ll fight them on the beaches” is the number one quote I’m given when I ask delegates at a seminar to tell me something Churchill said).

So rhetoric sometimes looks at the rules of grammar, screws them up and throws them in the bin. It deliberately uses incorrect grammar in order to be more effective and memorable. And to ‘jolt’ the brain into using ST and concentrating on what’s being said.  

How(and why) rhetoric works on the brain

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