The Em Dash: How One Punctuation Mark Became AI's Biggest Tell

A One-Character Turing Test

You've probably received an email from a colleague and thought: "Wait, there's a long dash in here... did ChatGPT write this?" If so, you're not alone. Since early 2025, the em dash has become the most famous marker of AI-generated writing.

The thing is, this idea is both completely understandable and utterly absurd.

A Punctuation Mark With 500 Years of History

The em dash, that long horizontal line — has been around since the 15th century. Dickens used it. Virginia Woolf used it. For centuries, it was a perfectly respectable typographic tool, beloved by literary writers and journalists alike.

In English-language journalism, the em dash is everywhere. The New York Times, The Atlantic, the Washington Post: quality publications use it extensively for parenthetical asides and narrative interruptions. It's a staple of polished prose.

And that's precisely where the problem starts.

Why ChatGPT Sprinkles Them Everywhere

ChatGPT was trained on billions of texts, a huge chunk of them from English-language publications that love the em dash. The model learned that em dashes signal "well-written text." And it applied that pattern across every language it generates, including French and German, where the em dash is far less common in everyday writing.

The result: when you ask ChatGPT to draft an email, a report, or an article, it scatters em dashes everywhere. Not because it wants to get caught, but because that's what its training data taught it to do.

The Birth of the 'ChatGPT Hyphen'

In early 2025, users on Reddit and X (formerly Twitter) started noticing this quirk. The "ChatGPT Hyphen" meme was born. On r/ChatGPT, screenshots piled up: resumes riddled with em dashes, suspiciously polished work emails, student papers betrayed by their punctuation.

Within weeks, the em dash became an informal litmus test. Spot one in a text? Probably AI. Teachers started using it to flag generated essays. Recruiters scrutinized resumes. Colleagues eyed well-punctuated emails with suspicion.

The Paradox That Should Worry Us All

Here's where it gets tricky. This widespread suspicion has an unexpected side effect. Writers, journalists, and authors who used the em dash long before ChatGPT existed are now being accused of writing with AI. Some have even started self-censoring, deliberately removing em dashes from their work to avoid raising red flags.

Sophie Vignoles, a linguist at Babbel, puts it well: "In an era of unprecedented creativity, humans are increasingly hesitant to write like humans." That's not a small thing. AI is impoverishing human writing, not by replacing authors, but by making certain stylistic tools look suspicious.

We've ended up in a situation where humans are adjusting their writing to avoid looking like machines. The world turned upside down.

OpenAI Acknowledges the Problem

In November 2025, OpenAI officially addressed the issue. Sam Altman called the fix a "small win." With GPT-5.1, users can now add a permanent instruction telling ChatGPT to avoid em dashes.

On Threads, OpenAI even had ChatGPT "apologize" with tongue firmly in cheek. The message was clear: the em dash had become enough of a PR problem to warrant a model update.

But here's the catch: it's not disabled by default. Users have to configure the option themselves. And fixing one stylistic tic doesn't address the deeper issue.

Why Punctuation-Based Detection Is a Dead End

The em dash was never a reliable marker of AI text. First, because plenty of humans use it. Second, because not all AI models overdo it: Anthropic's Claude and Google's Gemini are far more restrained.

More importantly, surface-level markers are too easy to fix. One prompt instruction and ChatGPT stops using them. Hunting for typographic "tells" to identify AI writing is like trying to spot a disguise by only looking at the shoes.

Real AI text detection relies on far subtler signals: narrative coherence, analytical depth, unexpected connections, the presence of a genuinely personal perspective. Things no punctuation mark can replace.

What This Story Really Tells Us

The em dash affair is more than a typographic footnote. It's a symptom of our collective anxiety about AI. We're looking for simple markers to distinguish human from machine, and we end up distrusting our own writing.

The answer probably isn't hunting for punctuation clues, but developing real critical thinking about the texts we read, AI or not. And above all, not letting a machine dictate which stylistic tools we're allowed to use.

The em dash survived five centuries of typography. It'll survive ChatGPT too.