Does an em dash mean AI wrote it?

The numbers

We counted em dashes in 3,379 texts. The table shows how many texts in each group contain at least one.

Why the gap is so wide in typed text

A keyboard has no em dash key. Typing one takes a shortcut that most people do not know, so people who want a dash reach for what is on the keyboard. In our typed human texts, 10% use a hyphen with spaces around it and 5% use a double hyphen. Models have no keyboard. They learned from edited prose, where the em dash is everywhere, and they use it freely.

When an em dash tells you little

• The text was edited or typeset. Books, journals and news sites use em dashes as house style. About 1 in 7 of our published human texts has one.
• The writer likes them. Plenty of people know the shortcut and have used em dashes for years.
• Software added it. Word and some phone keyboards turn two hyphens into an em dash automatically.
• The AI text was cleaned up. Replacing the dashes takes seconds. One dataset in our test was built that way, and its AI texts almost never contain one.

When it tells you more

An em dash is worth noticing in text that was supposedly typed in a hurry: a forum reply, a chat message, a quick email. It is worth more when it comes with other habits, such as leftover Markdown, a list of three in every paragraph or a string of words like "genuinely" and "crucial". One sign is a coincidence. Five signs are a pattern.

The short answer

An em dash in casual typed text is unusual for a person and normal for a chatbot, so it is a fair reason to look closer. It is not proof of anything. Our checker counts it as one sign among several, and the full list shows how each one was measured.