How to Use Hyphens in the Age of AI: Writing Rules and Tips

Like most punctuation, using hyphens correctly is tricky. Misplaced hyphens confuse readers and make even well-researched content look careless. Whether you write “a well known speaker” or “a well-known speaker” matters. And getting it wrong reflects poorly on your brand.

But here’s where things get interesting: AI writing tools have introduced a new punctuation challenge. If you’ve read any AI-generated content lately, you’ve probably noticed em dashes everywhere — sometimes multiple times per paragraph. While AI defaults to em dash overuse, human writers still struggle with basic hyphen rules.

With AI now generating more content than ever, understanding when to use hyphens versus em dashes isn’t just a grammar concern: It’s a content governance issue. In this guide, we’ll cover the essential hyphen rules, explain the em dash phenomenon, and show you how to maintain punctuation standards at scale.

Key takeaways

• Hyphenate compound adjectives before nouns (e.g., cat-friendly apartment), but don’t overuse hyphens with prefixes or after adverbs.
• The em dash explosion in AI-generated content has made punctuation choices a brand authenticity issue — not just a grammar concern.
• Use governance platforms like Markup AI to enforce complex punctuation rules at scale, catching both hyphen errors and AI’s tendency to overuse em dashes.

What’s a hyphen?

A hyphen (-) is a punctuation mark that’s used to connect words or parts of words:

• “My cousin is a thirty-five-year-old jack-of-all-trades.”
• “A time of self-reflection about one’s decision-making skills.”
• “A feeling of short- and then long-term regret.”

General rules on when and when not to use hyphens

Do use hyphens with compound adjectives that appear before nouns

Any time you stack two or more words together in front of a noun, so that they collectively function as an adjective, you’ve created what’s called a compound adjective. Compound adjectives are generally hyphenated:

• “He’s looking for a cat-friendly apartment.” 
• “She had a very matter-of-fact expression on her face.”

The key is that those compound adjectives need to come before the noun they’re modifying. Otherwise, you don’t use hyphens:

• “He’s looking for an apartment that’s cat friendly.”

And while you can use multiple words in your compound adjectives:

• “A hard-to-find place” 
• “A soon-to-be-forgotten example” 

You want to avoid overdoing it. For example:

• “An around-the-world-all-expenses-paid-once-in-a-lifetime vacation.”

Remember: Don’t use hyphens with adverbs:

• Incorrect: The cleverly-disguised detective. 
• Correct: A mercifully short example.

Do use suspended hyphens to avoid redundancy in a series

Imagine you’re describing a new kind of fabric. Sure, you could write:

• “We’re selling a new stain-resistant, wrinkle-resistant, and odor-resistant fabric.”

However, a more concise way to express the same idea is to use suspended hyphens:

• We’re selling a new stain-, wrinkle-, and odor-resistant fabric.

Do use hyphens for ages and numbers

When expressing age and numbers, the key is to determine if the phrase acts as a single descriptive unit (a compound adjective) placed directly before the noun.

Hyphens are only necessary in these expressions when the age or number is used as a compound adjective before a noun:

• A 10-year-old boy
• A 5-mile race

Also, hyphenate numbers when written out or expressed as a fraction, but not when expressed as percentages:

Q: If twenty-eight people came to the party and two-thirds got drunk, what percentage of them woke up with a hangover the next day?

A: 66 percent.

Avoid hyphens with prefixes (most of the time)

Resist the temptation to hyphenate any word that starts with a prefix:

• Write coauthor, not co-author 
• Write nonviolent, not non-violent 
• Write reedit, not re-edit

Having said that, there are many exceptions. Here are two rules to help you find the more common ones:

1. Use a hyphen before a capitalized word or a numeral (pre-Columbian, post-1970).
2. Use a hyphen to separate two i’s, two a’s, and other combinations of letters that could easily be misread, such as anti-inflammatory or mega-annoyance.

What’s an em dash?

An em dash (—) is a longer punctuation mark used to create emphasis, insert interruptions, or set off additional information within a sentence. Unlike hyphens, which connect words, em dashes separate ideas — often dramatically:

• “The project deadline — originally set for March — has been moved to June.”
• “She had one goal in mind — finish before sunset.”
• “The report covered three key areas — revenue, costs, and growth projections — in exhaustive detail.”

The em dash phenomenon: When AI gets carried away

If you’ve been reading AI articles, marketing copy, or even internal documentation lately, you’ve probably noticed an overwhelming presence of em dashes. What’s happening?

Why AI loves em dashes

Large language models like ChatGPT and Claude have been trained on massive datasets of published text—  including literary fiction, journalism, and formal writing where em dashes appear frequently for stylistic effect. As a result, these tools default to em dashes when they want to:

• Add emphasis or dramatic pause
• Insert clarifying information mid-sentence
• Create a conversational, flowing tone
• Avoid the decision between commas, parentheses, or colons

The problem? What works sparingly in a novel doesn’t always work in business content and when AI uses em dashes in every other paragraph, it becomes a recognizable pattern that undermines authenticity.

Should you use em dashes in your content?

Em dashes aren’t inherently bad. Used intentionally, they add energy and emphasis to your writing. But here’s when to reconsider:

Avoid em dashes when:

• You’re using them more than once per 200-300 words
• They’re replacing standard punctuation (commas, colons, semicolons) that would be clearer
• Your content needs a formal, authoritative tone
• You’re trying to disguise AI-generated content as human-written

Use em dashes when:

• You genuinely want to create dramatic emphasis
• You’re inserting an unexpected twist or contrasting idea
• The interruption adds to readability rather than disrupting it
• Your brand voice is conversational and modern

Using hyphens (and dashes) properly makes content better — period

Getting hyphen usage right is key to clear and professional writing. The readability of your content improves dramatically when you avoid common mistakes like misplacing hyphens in compound adjectives, overusing prefixes, and letting AI scatter em dashes throughout your content without intention.

As AI generates more of your content, punctuation consistency becomes a governance challenge, not just a proofreading task. Markup AI’s specialized Content Guardian Agents^SM like the Spelling & Grammar Agent — are built to automatically enforce these complex, rule-based standards across your entire enterprise content operation. This means tricky punctuation like hyphens is flawless every time, and AI-generated content gets refined to match your brand standards before it ever reaches your audience.

How you punctuate isn’t just about correctness. It’s about whether your content sounds authentically human or obviously machine-generated. Markup AI helps you standardize your grammar use across all content, sign up for a free trial to learn more. 

Frequently asked questions

What are the four hyphen rules?

1. Compound adjectives before nouns (for example, “customer-focused approach”).
2. Avoid ambiguity (for example, “re-cover” vs. “recover”).
3. Use with prefixes like “ex-” or “self-“.
4. Clarify compound numbers and spelled-out fractions.

How do you use a dash in a sentence?

Dashes add emphasis or break up thoughts. Markup AI helps make sure they’re not misused in place of commas or colons.

How do you know if a sentence needs a hyphen?

If two or more words describe a noun together (before the noun), a hyphen may be needed. Markup AI provides real-time guidance on these rules.

What are the different types of dashes?

Dashes can be used in a variety of ways, including: 

• Hyphen (-): Connects words (e.g., “well-known author”)
• En dash (–): Shows ranges (e.g., “pages 10–15”)

Em dash (—): Creates breaks or emphasis (e.g., “We had one chance—and we took it”)