Unpacking CMOS: Hyphens, En Dashes, and Em Dashes

Emily Fahey Technical Writing, Writing Tips

Hyphens, en dashes, and em dashes—oh my! They may look similar (especially when working in front of a computer screen) but they each serve a distinct purpose, and their correct use shows attention to detail in professional writing.

What is the difference between hyphens and dashes anyway?

CMOS 6.75 includes a great visual so you can see the distinction between hyphens, en dashes, em dashes, and even 2-em and 3-em dashes in print. 

Here is a simple explanation for general use:

  • Hyphens are used to connect two words that function together as a single concept. 
  • En dashes connect things that are related to each other by distance, usually a numerical range, though they are also used to connect a prefix to a proper open compound. 
  • Em dashes are used to separate a specific element in a sentence, similar to the way parentheses function but with more emphasis. They can also be used as an alternative to commas or colons when an abrupt break is used in a sentence.

Let’s dive further into the particulars of using hyphens, en dashes, and em dashes correctly.


Phrasal Adjectives

CMOS 5.92 explains that phrasal adjectives (also known as compound modifiers) are hyphenated phrases that act as a unit to modify a noun. This is used as an important distinction to avoid confusing the reader. 

Consider the way the following sentence changes meaning with and without the hyphen:

My new neighbor is a big-cat zoologist.

My new neighbor is a big cat zoologist.

In the second example, it is unclear as to whether the adjective “big” is referring to the cat or the zoologist. Think of this example as the hyphen version of an “eats, shoots and leaves” situation. Correct use of the hyphen can help you avoid awkward or incorrect interpretations of your writing. 

Hyphens, en dashes, and em dashes, oh my! Correct usage of each shows care and attention to detail in your writing. #unpackingcmos #writingtips Click To Tweet

But what do you do if a compound noun is an element of a phrasal adjective or if more than one phrasal adjective modifies a single noun? CMOS 5.92 rescues us again with the reminder that in these cases, the entire compound noun must be hyphenated to clarify the relationship between words. For example:

My best friend is enjoying being a stay-at-home dad this year.

Hyphenation Guide

CMOS 7.89 notes that hyphens should be used sparingly. When in doubt about spelling a word with spaces, hyphenating, or using a compound word, reference CMOS or Merriam-Webster’s Collegiate Dictionary. The CMOS hyphenation guide is a great shortcut when you need to do a quick reference check.

En Dashes

En dashes are primarily used to connect numbers and occasionally words.

Used as To

CMOS 6.78 instructs that when referencing continuing numbers (dates, times, or number ranges), an en dash signifies up to, including, or through. Consider the following examples:

You are cordially invited to a pajama party at Leanne’s house to watch the royal wedding live on April 29, 2011, 3:00–6:00 a.m. 

Material for your final exam will be covered in chapters 6–13 in your textbook.

The exception is when the number range is preceded by the words from or between. In these cases, use the word and or to, never an en dash. Consider the example below:

Incorrect: She lived in L.A. from 2008–2011 while trying to become an actress.

Correct: She lived in L.A. from 2008 to 2011 while trying to become an actress.

CMOS 6.79 further clarifies the use of en dashes in an unfinished number range, such as the date range for a serial publication or the age range of a living person. See the following example:

The Selected Works of T. S. Spivet by Reif Larson (1980–) received an advance of just under a million dollars from Penguin Press after a bidding war involving ten publishing houses.

Rare Uses

Sometimes an en dash may be used in place of a hyphen or even a comma, and while this is acceptable, it often comes down to a choice of style, personal preference, and sentence clarity.

CMOS 6.80 shows how an en dash can be used in place of a hyphen in a compound adjective when one element is an open compound or when both elements consist of hyphenated compounds. Hyphens function to join two words, whereas an en dash in these cases signals a link across more than two words. Take the following example:

I’ve been reading a new author who displays an Ernest Hemingway–style terseness. 

While the sentence above is grammatically correct, it would be clearer if rewritten rather than relying on an en dash, like so:

I’ve been reading a new author whose terse writing style reminds me of Ernest Hemingway.

CMOS 6.81 demonstrates how en dashes may be used when denoting specific campus locations for a university, such as the University of Wisconsin–Madison vs. the University of California, San Diego. In this case, the choice to use either an en dash or a comma is a stylistic one, but once a decision is made, it should be done consistently. If you’re unsure what style to use, defer to the university’s style guide.

Em Dashes

The em dash is incredibly versatile and has more complex rules around usage with other punctuation marks, as compared to hyphens and en dashes.

To Explain, Amplify, or Separate

Em dashes can be used to set off explanatory or amplifying portions of a sentence, as described in CMOS 6.85. Always remember, though, that em dashes should never be used within or immediately following another element that is also amplified by em dashes. See the following example:

Her favorite authors wrote fiction about everyday life for women and girls in the late 1800s and early 1900s—L. M. Montgomery, D. E. Stevenson, and Maud Hart Lovelace.

CMOS 6.86 demonstrates how an em dash can be used to separate an introductory noun or series of nouns from a pronoun. For example:

Green olives, cheddar cheese, and pineapple—this was the alarming grocery list she gave him!

Em dashes can also be used to indicate a break in thought or an interruption in dialogue, as seen in CMOS 6:87 and demonstrated below.

“Did he—did he make it on the flight safely?” she asked with a catch in her throat.

Used with That Is, Namely, For Example, and Similar Phrases

An em dash can be used in front of certain phrases, as noted in CMOS 6.88. Note this example:

A mnemonic device is a helpful and fun tool for children studying for tests—for example, Never eat shredded wheat is a rhyme for remembering that the principal points of a compass are north, east, south, and west, in clockwise order.

Beyond the Single Em Dash

Anyone familiar with the writing of Jane Austen, the Brontë sisters, and their contemporaries has witnessed the 2-em dash. While not often used in contemporary writing, the 2-em dash represents a missing word or part of a word, often omitted to disguise the name of a place. Take the following example from chapter 16 of Pride and Prejudice:

The officers of the ——shire were in general a very creditable, gentlemanlike set, and the best of them were of the present party; but Mr. Wickham was as far beyond them all in person, countenance, air, and walk as THEY were superior to the broad-faced, stuffy uncle Phillips, breathing port wine, who followed them into the room.

While not often used in contemporary writing, the 2-em dash is recognizable in the work of Jane Austen and her contemporaries. #unpackingcmos Click To Tweet

The 3-em dash is also used in a limited capacity, primarily in a bibliography, where it is followed by a period and represents the one or more authors or editors named in the preceding entry.

CMOS is a treasure trove for detailed answers and explanations for the finer points of hyphen, en dash, and em dash usage. Just remember the cardinal rule (in our opinion, anyway): never EVER use multiple hyphens instead of proper en and em dashes. If you need a shortcut, use Alt+0150 for an en dash or Alt+0151 for an em dash on a PC (Option-Dash for en dash and Option-Shift-Dash for em dash on a Mac). Your fellow CMOS lovers will thank you.


Need someone to review your hyphens? Are you worried that you use too many em dashes? Still not sure if you’re using en dashes correctly? We can help. Contact the Scribe Source today for information on editing and proofreading services.

About the Author

Emily started her career as a fundraising professional working in higher education and public media. She specializes in writing direct mail and email fundraising appeals, website copy, marketing materials, training manuals, and blog content. Emily first joined the team in 2014; she now coordinates all the Scribe Source’s writing projects.