Lexical Density, Why You Can't Write Like You Speak, and Why Grammar Actually Does Matter
Updated: Mar 10
The little known metric that disproves two widely preached copywriting tips.
Last week I posted on LinkedIn about the flaws in the common pieces of copywriting advice “write like you speak” and “grammar isn’t important”. You can read the full post here.
I based my points on common sense backed by my experience as a copywriter. But I actually came across a metric that backs up my points with data.
That metric is lexical density.
Lexical density is the number of content words (i.e. noun, verb, adjective and adverb) per clause.
Most verbal communication is actually non-verbal, you don’t need as many content words for the listener to follow along (i.e. you can keep up without constantly referring back to the nouns you’re talking about).
That means, on average, spoken language has a lower lexical density than written language.
Here's how this plays out
Below is a transcript of an interview with a subject matter expert for a restaurant client's blog that I wrote.
You'll see the original transcript and then what the blog turned into, as well as the corresponding lexical density for both.
Transcription from an SME about shaken vs. stirred martinis
“The weight of the shaker…yeah they’re weighted…and the ice kind of it’s essentially slamming back and forth and your tin is crushing it into really small bits…yeah yeah they melt faster…So people look at that and they’re like oh you're taking away from some of the flavor of the spirit…In this case gin and like…masking the flavor…I guess they're calling it bruised when it's actually just really small ice chips and over dilution…”
Lexical density: 46.25%
Some gin martini aficionados argue that shaking a martini bruises the gin. What’s actually going on is dilution. The weight of the tin crushes the ice into very tiny pieces (this doesn’t happen when you stir a martini).
These tiny pieces then melt very quickly and dilute the gin. This can take away from or “mask” the flavor of the gin. But bruise it? No. Even if that were the accurate term, anyone worried about bruising their gin should probably go outside and touch some grass.
Lexical density: 53.49%
As you can see, there's a 7% increase from spoken to written in the example above. (There are many online tools to measure this, I use this one.)
Seven percent might not seem like much. But according to a study on readability and lexical density, readability takes a hit (see table 5) when lexical density drops below ~36% and goes above ~46%.
Meaning, a 7% difference within a 10 point range is huge.
And while the above example is content writing, not copywriting (a topic that warrants its own post), there are two reasons why that actually doesn't matter:
Sentence length doesn’t dictate lexical density. Lexical density is per clause, not sentence. “Apple” has a lexical density of 100%. “Granny Smith Apples are usually green, but sometimes they can be more yellow in hue depending on when they were picked,” has a lexical density 52.38%. A larger sample size of sentences is required to demonstrate the point.
Translation is required for both types of writing. Knowing how to take spoken subject matter expertise or customer anecdotes and translate them into written material is a necessary skill for both content and copywriting.
In order for someone to follow spoken content in a written format, the writer must increase the lexical density. Everyone naturally does this, even those who say to “write like you speak” and that “grammar doesn’t matter”.
So how is this accomplished? How do you take spoken material and translate it into written?
You do this by adding or removing certain parts of speech. In other words, you do this through grammar.
Now, do you need to understand to know what lexical density is to write effectively, copy or otherwise?
Absolutely not. That would be absurd.
The point is, whether you're aiming for a “smart and professional yet friendly” tone in your cold email or trying to capture someone’s voice while ghostwriting a memoir, it’s all the same.
Both require a grasp of the English language and its rules and both must go through a grammatical transformation.
At the end of the day, “write like you speak” and “grammar doesn’t matter” are trite tips that you’ll most likely find in a Twitter thread on how to grow your following, or a personal branding LinkedIn post that reads like you’re riding shotgun with someone who just learned to drive stick.
You’ll also find marketers who’ve taken it upon themselves to become copy critics dishing "write like you speak", not so much "grammar doesn't matter".
Both groups one of two things in common (sometimes both):
They don’t write copy for clients besides themselves
They’d crack like cheap glass if they tried
No self respecting copywriter should be taking advice from someone who doesn't regularly do battle with a blank page on someone else's behalf.
“Write like you speak” is akin to saying “make more money” or “add value”. Saying “grammar doesn’t matter” would be like carpenters claiming they don't care what tool they use or a contractor claiming building materials don’t matter.
So I’d actually argue that they’re not really advice at all, as they’re neither actionable nor true.
Make sure your copywriters are more interested in knowing the nuances and complexities of the English language than they are dissing their grade school English teachers.
And unless you both have the exact same target audience, make sure your copywriter isn’t a one-trick pony.
Often what people mean when they say “write like you speak” is “write more simply”. But even that advice demands context, which I'll cover in a subsequent post.
How this fits in with brand voice
That last line in the martini example above might seem cheeky ("...anyone worried about bruising their gin should probably go outside and touch some grass"), and it is.
But what you don’t see is the rest of the blog post or the restaurant’s website or their emails.
The two thousand or so words prior makes up one of the most in-depth breakdowns of the history of the martini that you’ll find online, including research from three martini books (yes, actual books) and a link to an 1888 cocktail recipe book, as well a page reference to the recipe that’s discussed.
Their website has some cheek but for the most part it’s pretty tame.
They can afford to crack a joke like the above for two reasons:
They brought the heat beforehand. A lot of rules that apply in one context go out the window, when you have demonstrated expertise and deliver massive value.
It’s on brand. Their brand voice takes swings at four types of entities:
People who sit at the bar and complain that there’s no TV, instead of connecting with the people they came with
“Mixologists” who take themselves too seriously (not to be confused with not taking themselves seriously)
People who take themselves too seriously
Alcohol companies that use “small-batch” as a marketing ploy when there are family-owned alcohol companies that go back several generations whose only option is small batch since their recipes and processes are so complex that they’re actually impossible to scale
And that's it. Everyone else gets 5-star hospitality, no questions asked. The people above get 5-star hospitality too, but not before we've poked a little fun at them.
The restaurant has a very specific brand voice. They’re a fun, nuanced hybrid that leads with their authority in the cocktail space but they’ve got a little "wise guy" in them (the restaurant has a slight 20s vibe).
Many of their customers are Baby Boomers in the surrounding neighborhood. They're thrilled to have a swanky place to grab the “best martini they’ve ever had,” and they appreciate the no-nonsense approach versus the typical millennial and gen Z coddling that many brands resort to.
The brand voice was inspired, in part, by their beverage director who knows more about spirits and wine than any human should.
I say in part because I aimed for something slightly more elevated and academic.
I wanted any well-read, college educated cocktail connoisseur who wouldn’t last two seconds behind their bar, or in the restaurant industry for that matter, to think twice before challenging their expertise.
I wanted to establish authority.
In other words, I made a conscious decision to not write like he spoke because of my objectives. I made this same decision when I translated the SME’s voice into the blog material.
Effective copy knows the rules, how to break them, and when. But effective brand voice establishes and holds true to them.
Both must always be tied to an objective.
Whether you do it consciously or unconsciously, writing like you speak requires a process. You cannot do so without understanding how to manipulate and work with grammar.
Think twice before following any claimed online writing gurus who tell you differently. They're usually not malicious, but they most likely don't write copy outside of their own social media posts or emails.
Copy critics, on the other hand, until they're actually held accountable for driving results with their "suggestions," they can absolutely take a hike.