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Hyphens and Dashes

16th March 2026

With AI tools becoming widely adopted, em-dashes have become a telltale sign of AI-generated content. Claude and ChatGPT seem to love them, which is unfortunate, because it’s now made everyone suspicious of a perfectly good punctuation mark. But this doesn’t change the fact that most people (non-native and native English speakers alike) never learned or understood the difference between hyphens (-), en-dashes (–), and em-dashes (—) in the first place. I now frequently see correct usage (AI-generated) and incorrect usage mixed in the same document, which happens when people do not understand the difference and revise a piece of AI-generated text.

The differences may seem subtle at first, but incorrect usage is unprofessional and can change the meaning of a sentence. Once you understand the distinctions, it’s hard to unsee when people use them incorrectly. There is also a trust dimension to this. As a reader, if someone didn’t put in the effort to write correctly, how can I trust that they put in the necessary effort into the thinking behind what they wrote?

I first learned about these distinctions during my PhD when I started writing scientific papers. David Norris, my supervisor and a great writer, had a habit of returning our manuscripts with red ink covering almost every page but rarely any explanations. You were expected to figure out what was wrong. Freddy Rabouw, then a postdoc in our group, took the feedback he received seriously, dug into the rules, and created a short presentation for the whole lab. The rules are simple once you learn them, but nobody teaches them.

When to Use Which

The best single resource I know is Typography for Lawyers. Here’s my condensed version with tech-world examples.

Hyphens (-) connect compound words and phrasal adjectives: AI-generated text, real-time processing, third-party API. The logic is that when two or more words work together to modify a noun, you hyphenate them before the noun. “An AI-generated response” but “the response was AI generated.” One exception: don’t hyphenate when an adverb ending in -ly does the work. It’s highly scalable infrastructure, not highly-scalable infrastructure.

Missing hyphens can create genuine ambiguity. Consider “small business software”: is it software for small businesses, or small software for businesses? With a hyphen, small-business software is clearly software for small businesses. Or “new user onboarding”: is the onboarding new, or are the users new? New-user onboarding removes this ambiguity. In AI contexts, “few shot prompts” could mean a small number of shot prompts, whatever those are; few-shot prompts makes clear we’re talking about prompts for few-shot learning.

En-dashes (–) are slightly wider and are used in two cases. First, they mark ranges: 2020–2023, pages 50–75, chapters 3–7. (But if you start with “from,” use “to” instead: from 2020 to 2023, not from 2020–2023.) Second, they denote connections or contrasts: product–market fit, the London–New York route, key–value cache.

Em-dashes (—) create a break when commas are too weak, but colons or semicolons feel too heavy. Used well, they add rhythm and emphasis, but overused, they make text feel breathless, repetitive, and AI-generated (yes, this is a compound modifier too!).

A Bonus Tip for the AI Age

Maybe incorrect usage of hyphens is now a charming sign that someone actually wrote it themselves. Some people have caught on and started find-replacing all em-dashes with single hyphens (-) or double hyphens (--) to hide that they used AI, which is its own tell. But this still doesn’t hide the most obvious giveaway, which isn’t the em-dash itself. LLMs almost always put spaces around em-dashes: “word — word” instead of “word—word.”

My guess is the models are overtrained on news data, and the AP style guide, which is most commonly used in journalism, recommends spaces around the em-dash. Books and most professional writing use them without spaces.

I’d been avoiding em-dashes entirely for the past year because of this association—noticing the space pattern finally lets me reclaim them for my own writing.