You have probably seen it. A sentence flows along normally, then interrupts itself with a long horizontal mark, and then picks up again.
That mark is the em dash (—).
For most of its 600-year history, the em dash was a quiet tool used by printers and novelists. Then large language models arrived. Suddenly, em dash AI writing was everywhere. Not in literary essays or longform journalism. In everything. Job application emails. Press releases. Social media captions. Customer service replies.
Writers and editors started noticing. Researchers started measuring. And the em dash became the most recognizable visual signal that a piece of text was written by an AI.
This article covers the complete history of the em dash, how to use it correctly, and why it became the punctuation mark that could expose a chatbot. It also covers something most em dash articles miss entirely: what the em dash does to users who rely on screen readers, and why its overuse is a genuine accessibility concern.
Key Takeaways
- The em dash originated with 13th-century Italian rhetoricians and was standardized by 15th-century printers. It was an invention of the print shop, not of grammarians.
- Its name comes from the em, a typographic unit equal to the width of the capital letter M.
- The em dash has four legitimate uses: parenthetical asides, abrupt breaks in thought, replacing a colon for emphasis, and interrupted dialogue.
- ChatGPT uses the em dash at roughly three times the rate of human writers. This made it one of the most reliable early indicators of AI-generated content.
- OpenAI CEO Sam Altman confirmed a fix in November 2025. Users can now instruct ChatGPT to avoid em dashes via custom settings.
- Screen readers do not announce the em dash aloud. Multiple em dashes in a short passage fragment the reading rhythm for users of assistive technology.
- Good alternatives include commas, parentheses, colons, or simply restructuring the sentence.
What Is the Em Dash?
The em dash is the longest of the three dashes used in English typography.
The hyphen (-) is the shortest. It joins compound words and prefixes: well-known, re-enter, up-to-date. The en dash (–) is mid-length. It connects ranges and equal-weight pairs: pages 10–20, London–Paris, 2020–2025. The em dash (—) is the longest. It marks pauses, breaks, and strong asides within a sentence.
On a Mac, type it with Option + Shift + Hyphen. On Windows, use Alt + 0151. On most smartphones, hold down the hyphen key to reveal longer dash options.
Most style guides say not to put spaces on either side of an em dash. Some British guides allow a space before and after. American style, including the Chicago Manual of Style, recommends no spaces.
A 600-Year History
The em dash did not begin in a grammar textbook. It began in a print shop.
The earliest predecessor appears in the work of Boncompagno da Signa, a Florentine rhetorician writing in the early 13th century. He used a mark called the virgula plana, a flat horizontal mark, to indicate a long pause in vernacular Italian prose. Medieval scribes also used horizontal lines at the end of a page to signal that text continued on the next.
The dash as a standard typographic tool emerged during the 15th-century printing revolution. As Johannes Gutenberg’s movable type spread across Europe, printers needed practical tools to manage pauses, breaks, and editorial corrections within a line of type. They manufactured a metal slug one em wide. That slug became the em dash.
The name comes from the em, a typographic measurement equal to the height of a given typeface. In most fonts, that matched the width of a capital letter M. An em dash was a metal block exactly one em wide, fitting into the typeset line like any other character.
The em dash was invented by printers, not by grammarians. It came out of practical necessity in the print shop, not from any formal theory of sentence structure.
By the 18th century, the em dash had moved from the print shop into literary prose. British writers used it heavily in novels, letters, and essays. By the 19th century, it was a standard part of the English writer’s toolkit. You can read more about its full typographic lineage at PublishingState.com’s history of the em dash.
The Writers Who Loved It
The em dash attracted some of the most distinctive literary voices in English.
Emily Dickinson is the most famous example. She used the em dash so obsessively that editors spent decades debating what to do with her manuscripts. Where other writers used commas, periods, or semicolons, Dickinson used dashes. Her poems often carry no other punctuation at all. Thomas H. Johnson’s 1955 scholarly edition was the first to preserve her dashes rather than replace them with standard punctuation.
Henry James used the em dash to pile qualification upon qualification within a single sentence. His prose famously delays its point through successive interrupting clauses, each set off by dashes.
Virginia Woolf used dashes to mirror the movement of thought. Her sentences break and restart the way a mind actually does, without warning and without apology.
Charles Dickens used them in dialogue to show characters cutting each other off mid-sentence, a technique that made his scenes feel theatrical and immediate.
These writers used the em dash purposefully. Each pause or break served a specific effect in a specific sentence. The contrast with AI overuse, where the em dash appears by habit rather than intention, is exactly the problem.
Four Legitimate Uses of the Em Dash
Used well, the em dash is a strong tool. It does things that commas and parentheses cannot quite manage. Here are its four main legitimate applications.
1. A strong parenthetical aside
When you want to add information and parentheses feel too formal while a comma feels too weak, the em dash works well.
Example: “The meeting — which nobody had requested — ran ninety minutes.”
This is more emphatic than a comma pair and less clinical than parentheses.
2. An abrupt break in thought
The em dash signals that a sentence changes direction sharply.
Example: “She was halfway through the sentence when — nothing. She stopped.”
3. Replacing a colon for emphasis
When you build toward a conclusion, the em dash delivers it harder than a colon.
Example: “There was only one acceptable outcome — a full refund.”
4. Interrupted dialogue
In fiction, an em dash at the end of a speech signals that another character cuts in before the sentence is finished.
Example: “I was going to say — ” “You were not going to say anything useful,” Maria replied.
Most style guides recommend no more than two em dashes in a single sentence. More than that and the sentence becomes hard to follow.
Em Dash AI Writing: How ChatGPT Got Addicted
ChatGPT launched in November 2022. Within a year, writers and editors had noticed something unusual: the model used em dashes far more than any human writer would. Em dash AI writing became a recognized pattern that editors and AI detection tools learned to spot.
The reason is training data. Large language models learn from enormous quantities of text scraped from the internet and from curated datasets. That text includes journalism, academic writing, book excerpts, and longform essays, which are genres where the em dash appears frequently. Models learn that the em dash is associated with quality, sophisticated writing. They deploy it constantly as a result.
Users noticed quickly. Social media posts in 2023 and 2024 started flagging the em dash as “the ChatGPT hyphen.” Editors working in publishing and content marketing began marking em dashes in submitted work as a warning sign. AI detection tools including GPTZero built em dash frequency into their scoring algorithms.
The em dash became a tell in the same way certain stock phrases did. As the Indiana Capital Chronicle reported in August 2025, people learned to spot machine-written text not by what it knew, but by where it paused and pivoted.
The Data: How Much More Does AI Use It?
ChatGPT uses the em dash at roughly three times the rate of typical human writing. If a paragraph of ChatGPT output contains em dashes in every second or third sentence, that pattern alone can raise a document’s score on AI detection tools by 15 to 20 points.
A 2026 study by SlopDetector measured dash density across more than 700,000 words of human prose compared to GPT-4.1 output. The gap was real but smaller than internet commentary suggested. The em dash alone is a weak signal. Combined with other markers including overuse of “however,” “moreover,” “it is worth noting,” and “delve,” it becomes part of a recognizable pattern that is harder to dismiss.
The em dash is also not the only punctuation quirk associated with em dash AI writing. Researchers have noted that AI models tend toward uniform sentence length and a high density of transition phrases. The em dash is the most visible of these patterns because it is easy to count in a quick scan.
OpenAI Acknowledged the Problem
For months, users asked ChatGPT to stop using em dashes. The model acknowledged the request and continued using them anyway. It was a frustrating loop: the AI understood what was being asked but could not reliably follow through.
In November 2025, OpenAI CEO Sam Altman posted about the issue on X and described a new fix as a “small-but-happy win.” Users could now add a custom instruction in ChatGPT settings specifying that the model should avoid em dashes, and the model would actually follow the instruction. TechCrunch covered the announcement when OpenAI confirmed the change.
The fix works but it is opt-in. Users who do not configure custom instructions, or who access the API without specific style guidance, still receive em dash-heavy output by default.
The broader implication is significant. Removing the em dash removes one of the most visible surface signals of AI writing without addressing the deeper stylistic habits that make AI text recognizable. Em dashes were a convenient shortcut for detection. Without them, identifying AI text becomes harder and requires more careful pattern analysis across multiple linguistic signals.
The Accessibility Angle Nobody Mentions
Here is something most em dash articles do not cover: what the em dash actually does to users who rely on screen readers.
Screen readers handle punctuation differently than sighted readers might expect. Most punctuation marks are not spoken aloud. They create a pause in the audio output. A period creates a longer pause. A comma or semicolon creates a shorter one. The em dash, when used correctly, functions as a mid-sentence pause and is not announced by the screen reader.
The problem is overuse. When a paragraph contains three or four em dashes, screen reader users experience a reading rhythm that constantly interrupts itself. The passage fragments into more pauses than it should have. This is especially disorienting in dense technical content, legal text, or instructional material.
Vispero, the company behind the JAWS screen reader, published specific guidance on dashes and AI-generated content because AI output had introduced a new pattern. AI paragraphs with em dashes every second or third sentence created audio experiences with an unusual rhythm that did not match reader expectations.
The en dash presents its own issue. Screen readers often interpret the en dash as the word “to,” which is usually the intended meaning in a range (2020–2025). An em dash is typically not announced at all. Writers who use em dashes in place of en dashes, or who stack multiple em dashes in a short passage, create audio experiences that do not match the intended meaning of the text.
For accessible web content, em dash restraint is part of good content hygiene. It is also one of those patterns that a professional screen reader accessibility test will surface, because it affects the listening experience for a share of your users that automated scanners do not easily measure.
Alternatives to the Em Dash
Whether you are trying to write more naturally, avoid em dash AI writing signals, or improve the experience for screen reader users, here are practical replacements.
Use a comma when the aside is light and the sentence can carry it without extra emphasis. Most parenthetical comments do not need an em dash. A comma pair handles the job cleanly.
Use parentheses when the additional information is supplementary and you want to signal that clearly. Parentheses tell the reader: this is here if you want it, but the main sentence works without it.
Use a colon when you are introducing a conclusion, list, or explanation. The colon is more formal but also unambiguous.
Restructure the sentence so the aside becomes its own sentence. This is often the cleanest option. Two shorter sentences are easier to read than one long one with an interrupting clause.
Use an en dash for ranges, scores, and relationships between equal-weight terms: 2020–2025, London–Paris, win–loss record.
None of these alternatives is inherently better or worse than the em dash. The point is to use each one with a reason, not by default.
The Bottom Line
The em dash is a genuinely useful punctuation mark with a 600-year history. It was invented by printers, adopted by novelists, and belongs in sentences where no other mark will do the same job.
It also became, for a period, the most recognizable signature of AI-generated text. Em dash AI writing is a real and measurable phenomenon. The em dash appeared so often in AI output that it stopped functioning as a stylistic choice and started functioning as a fingerprint.
Good writing is intentional. The em dash belongs in sentences where nothing else will do. If you reach for it as a general-purpose pause or transition, a comma or a period will usually serve better. Your readers, including those using screen readers, will have a cleaner experience.
If you want to understand how your web content performs for users who rely on assistive technology, our accessibility audit services cover content readability, punctuation patterns, and everything your screen reader users actually encounter during a real session.
The em dash is not the villain here. Careless writing is. Knowing the difference between a tool used well and a habit used thoughtlessly is what separates readable content from content that just sounds like it was generated by a machine.