The Em Dash: A History of a Mark Nobody Used — Until Everyone Did

Not your fault

This is a story about reputation — about how painstakingly it's built, and how instantly it can unravel the moment the wrong people start to admire you.

For nearly four hundred and fifty years, the em-dash labored quietly to earn its good name. In Shakespeare, it severed a sentence midway through. In Emily Dickinson, it let a line catch its breath. The newsrooms of the world's finest publications made it an unspoken seal of approval: where there was a dash, an editor had been there first. Four hundred and fifty years of labor leave a mark of their own.

Then came the language models. They devoured everything ever written — and somewhere in that feast, they encountered this particular symbol. They noted where it appeared, in which texts, in what company. They drew their conclusions. They went to work.

It was the highest form of flattery, and it destroyed the em-dash’s reputation.

In two years, four and a half centuries of hard-won respect crumbled to dust. The mark was blameless. So were the machines. The fault, as ever, lay with people.

The woman who spotted signs

In April 2025, a woman on LinkedIn complained about the em dashes cropping up in other people's writing — a dead giveaway of ChatGPT, she explained. Her advice: stay vigilant, edit the machine's fingerprints out, and strip the symbol on sight.

"I — keep — seeing — weird — long — dashes — in — posts."

— LinkedIn user, as quoted in Miles Klee, "Are Em Dashes Really a Sign of AI Writing?" Rolling Stone, April 11, 2025

She wasn't alone in her unease. Around the same time, a Reddit poster confessed to suspecting a colleague of using AI on the strength of the dashes alone, which they spotted in routine work emails. Soon after, the lifestyle podcast LuxeGen christened the em dash "the ChatGPT hyphen."

No one paused to ask where the mark had come from. No one recalled who had used it before ChatGPT, or why. The evidence was in hand — and that, apparently, was enough.

A lump of lead

In 1683, the London printer Joseph Moxon published a treatise on the craft of typography. Among its pages, he described a small metal block — the em quad, a piece of spacing material exactly one em wide. (An em is equal to the point size of a typeface, the measurement that governs every proportion of the set text.) This was engineering, not grammar: a unit of measure, a compositor's tool.

That's where the name em dash comes from, not, as the popular explanation goes, from the width of the letter M. The em dash was born as a piece of lead with genuine, physical heft.

It appeared on the page before it ever had a name. The year 1580 marks its first printed appearance, in a collection of letters. 1588 saw it enter drama. By 1623, in the First Folio, that sliver of metal was already performing with mastery, cleaving sentences at precisely the right moment. By 1733, it had gone thoroughly mainstream: Jonathan Swift mocked, in verse, the hacks who peppered their prose with fashionable dashes and italics — the mark's first turn as a badge of pretension rather than craft.

Then great literature arrived and restored its weight. Emily Dickinson turned it into breath itself. James Joyce threw out quotation marks and put the dash in their place. Over the centuries, a bar of lead evolved into an intricate, refined literary device.

Too long

The em dash's troubles began long before artificial intelligence entered the picture. In 1992, the Canadian typographer Robert Bringhurst published The Elements of Typographic Style — and showed the mark no mercy.

"The em dash is the nineteenth-century standard, still prescribed in many editorial style books, but the em dash is too long for use with the best text faces. Like the oversized space between sentences, it belongs to the padded and corseted aesthetic of Victorian typography."

— Robert Bringhurst, The Elements of Typographic Style, 1992, p. 80

In its place, Bringhurst proposed the en dash, flanked by spaces on either side. The industry split down the middle. The Chicago Manual of Style held its ground: the em dash, unspaced, the classic American standard. AP Style allowed the em dash but insisted on spaces around it. The British opted for the en dash and refused to recognize the em dash at all.

The argument raged on typography forums and in the pages of style guides. Writers spoke of intonation. Editors spoke of lazy syntax. Proofreaders spoke of technical requirements. Typographers spoke of aesthetics and the breathing room on a page. Thirty years on, the professionals still hadn't reached a verdict.

It wasn't on the keyboard

The em dash has no key of its own. Typing one by hand requires knowing a particular keystroke combination — arcane knowledge held by editors, proofreaders, journalists, and anyone who spent their days wrestling with text. Everyone else made do with a hyphen and thought nothing more of it.

This made the mark a badge less of formal education than of guild membership.

Editors, for their part, eyed it warily. In April 2011, Philip Corbett, the standards editor at The New York Times, counted the dashes on the front page: sixteen of them across six stories. A single item about the Mets alone packed in five dashes over three and a half paragraphs.

"It can seem like a tic; worse yet, it can indicate a profusion of overstuffed and loosely constructed sentences, bulging with parenthetical additions and asides."

— Philip B. Corbett, "Dashes Everywhere," The New York Times, April 5, 2011

That same year, Slate columnist Noreen Malone wrote:

"America's finest prose — in blogs, magazines, newspapers, or novels — is littered with so many dashes among the dots it's as if the language is signaling distress in Morse code."

— Noreen Malone, "The Case—Please Hear Me Out—Against the Em Dash," Slate, May 24, 2011

Editors fretted. Everyone else didn't know the mark existed.

Then ChatGPT arrived — and introduced it to the world.

They copied not the writer but the newsroom

Why language models fell so hard for the em dash remained a mystery for a long while. At first, everyone assumed literature was to blame: the machines had simply read their way through great American prose. That explanation turned out to be both wrong and incomplete.

For one thing, the algorithms weren't copying authors — they were copying standards. The New Yorker, The Atlantic, Harper's, and other names of that caliber all treated the em dash as routine. Training on their pages, the machine absorbed not the voice of any single writer but the voice of an immaculately edited magazine.

There was also a second, far deeper cause. The models had swallowed gigabytes of Markdown — a markup language where the hyphen serves as a load-bearing wall and a list boundary alike. To a machine, this was architecture, not punctuation. When developers demanded "smooth prose" from their neural networks, the habit of structuring everything didn't simply vanish — it shapeshifted. The em dash became the perfect loophole: a legitimate literary mark that let LLMs build sentences with the same rigid logic as code. The machine smuggled its architecture in under the cover of fine writing.

Then people stepped in. In the final stage of training, human testers read the machine's output and chose the best of it. They liked precise, structured prose that read as "smart." The em dash conjured the illusion of sophisticated human thought, so the testers kept clicking "approve," cementing the pattern with every click. OpenAI's Sam Altman would later admit that the frequency of em dashes in ChatGPT had been artificially inflated for exactly this reason: users liked it.

By 2026, the scale of the anomaly had been measured in hard numbers. Where the average human writer used 3.23 dashes per thousand words, Claude Opus 4.6 produced 9.09 and GPT-4.1 a record-setting 10.62. Meta, by contrast, had scrubbed the mark out during training itself: across the Llama 3 family, the figure sat at zero.

The harder a machine tried to sound intelligent, the more dashes it deployed, and the more often the human eye stumbled over them.

A witch hunt

In February 2025, an X user named @PaulSkallas posted: “the easiest way to spot AI-generated text is the em dash.” Within days, tens of thousands of people had seen the statement.

What followed was an avalanche. Reddit filled with threads of people airing suspicions about colleagues and the writers behind popular newsletters. LinkedIn sprouted guides on how to sniff out AI in a candidate's résumé. Teachers began returning student papers marked "em dash = ChatGPT." Writers on Substack publicly swore off the mark, unwilling to look suspect. Some went back and combed through their old work by hand, scrubbing out every em dash they found.

OpenAI reacted. In November 2025, Altman posted on X about a "small but satisfying win": users could now disable the em dash in ChatGPT's settings. Shortly after, an apology went up on OpenAI's official Instagram — one the company had assigned the neural network itself to write.

"I'm sorry. Truly. The em dash was supposed to be a classy little pause — a soft dramatic flourish — not a neon sign that says 'This was written by AI at 2am.' Things got out of hand."

— ChatGPT, official Instagram, November 2025

The apology contained em dashes. Users noticed.

It’s worth repeating that the detector existed long before AI did. In 2011, Corbett was counting dashes on the front page of The New York Times, and Malone was invoking Morse code. The problem of overuse was old news — the neural networks simply took it to a new level and introduced it to a global audience.

Researcher Przemysław Czuma analyzed 69,632 scientific preprints on the medical platform medRxiv, with publication dates spanning 2020 to 2025. Before ChatGPT's launch, the em dash appeared in 4.23 percent of papers. By 2025, that figure had climbed to 20.30 percent. The growth was concentrated in the narrative sections — precisely where scientists explain their results in their own words. Precisely, that is, where a scientist is supposed to think for themselves.

A quiet, unremarked rehabilitation

In July 2026, The Economist published a study. The editors asked four language models — ChatGPT, Claude, Gemini, and Grok — to rewrite articles pulled from the magazine's own archive. The resulting corpus ran to 55,940 sentences and 1.2 million words. Then researchers measured the old texts against the new.

The result was unexpected. Of the four models, only Claude used the em dash more often than human writers. ChatGPT, meanwhile, used it less than anyone else in the study — humans included. Note the irony: a mark treated as damning evidence for two straight years had quietly stopped being evidence at all, simply after a routine update. While people were still learning to spot the em dash, the models were already shedding it.

By this point, the real fingerprints of machine-generated text were entirely different. Models favored long words where people reached for short ones. They turned verbs into nouns — not "expand" but "expansion," not "investigate" but "investigation." They rationed commas and steered clear of parentheses. They loved the "not A, but B" construction, and they adored triads, because triads sound more persuasive. The evidence was still there — it just no longer included the em dash.

Human writers, meanwhile, began cautiously reclaiming the mark. The Economist closed its piece this way:

"Many believe LLMs stuff their prose with em-dashes, but that is not true after the most recent updates. Today only Claude uses more em-dashes than human writers, with ChatGPT using markedly fewer than any other writer in our study. Humans rejoice — and start using dashes again."

— "How to Spot AI Writing," The Economist, July 30, 2026

The mark's return, however, will be neither easy nor swift. Its reputation has taken real damage, and everyone knows it. The rehabilitation is complete. The bad taste lingers.

Drawing a line under it

The mark spent centuries earning its reputation. Then the machines arrived and seized on the em dash for precisely that reason — it had become a signal of quality. Language models weren't copying writers but institutions: floor upon floor of professionals working from morning until night to make text exemplary (and, sometimes to excess, dressing it up with em dashes along the way). That, after all, is exactly what separates edited prose from something thrown together in a hurry.

This is where the mistake lies, but the machines weren't the ones who made it. They simply worked out, in short order, what most people had failed to grasp in four hundred and fifty years: what this odd little stroke actually is, what it's for, what function it performs, and where it belongs in a sentence. Most people — unlike the language models — had never read anywhere near enough good prose, so they met the em dash for the first time in a wall of ChatGPT text and drew the only conclusion their education and intellect allowed.

The em dash is not to blame.

Nor are the machines.

The blame lies with the idiots — and there are no fewer of them now than over the past four hundred and fifty years.

If anything, there are more.