A hyphen ( - ) is used primarily to join two or more words to form a new, compound word or to provide clarity when using certain affixes (such as prefixes). Hyphens also have certain technical uses, such as indicating a range of numbers or combining multiple sets of numbers together into a single unit (as is often done with telephone numbers).
Because a hyphen unites multiple things into a single element, we do not put spaces on either side of it (except in one specific circumstance known as a hanging hyphen, which we’ll discuss later on).
Forming compound words
A compound adjective (also known as a compound modifier or a phrasal adjective) is created by two or more words that work jointly to modify the same noun. They can be composed of various combinations of adjectives, nouns, quantifiers, and participles, with a hyphen appearing between each word that is used.
Adjective + Adjective
- “Look in the top-right corner of the screen.”
- “She had bright, blue-green eyes.”
- “I need you to print 20 black-and-white copies of the contract.”
Adjective + Noun
- “They went on a wild-goose chase.”
- “I can only find part-time work at the moment.”
- “Do you have any sugar-free cookies?”
Noun + Noun
We usually join two nouns with the conjunction and to make them into a compound adjective.
- “I find her salt-and-pepper hair very attractive.”
- “These old brick-and-mortar buildings have stood the test of time.”
Quantifier + Noun
- “It is the only 10-storey building in the town.”
- “The eight-pound bag fell to the floor.”
- “The theater has a 400-person capacity.”
Past and present participles can be paired with adjectives, nouns, and adverbs to form compound adjectives.
- “Many legends still survive about man-eating whales, but they are simply untrue.” (present participle + noun)
- “My old-fashioned aunt would never approve.” (adjective + past participle)
- “We have well-intentioned neighbors, but they can be a bit nosy sometimes.” (adverb + past participle)
- “Our eyes had to adjust in the dimly lit corridor.” (adverb + past participle)
When not to use a hyphen
Notice that, in the last example above, dimly lit is not hyphenated. Adverbs ending in “-ly,” as well as the adverb very, do not take a hyphen in compound constructions because it is always clear that they are modifying the adjective or participle that follows them. For example:
- “There are many beautifully constructed houses in this neighborhood.”
- “Margaret is a very bright student and a wonderfully talented pianist.”
Be careful not to apply this rule to adjectives or nouns that end in “-ly”—these will take a hyphen in a compound adjective, as in:
- “My uncle helped refugees escape to ally-controlled countries during the war.”
- “My brother was a sickly-looking kid growing up, but he has become one of the top athletes in the country.”
Also note that we generally don’t use a hyphen with compound adjectives when they appear after the noun they are modifying. For example:
- “My aunt is rather old fashioned.”
- “This bag weighs eight pounds.”
- “We’re looking for a place to eat that is family friendly.”
- “Our neighbors can be a bit nosy, but they are well intentioned.”
Be careful though, because this is not always the case—some compound adjectives always (or often) remain hyphenated, even when they appear after a noun. For instance:
- “Her eyes are blue-green.”
- “Are these cookies sugar-free?”
- “I try to avoid food that is mass-produced.”
If in doubt, try searching for the compound adjective in a dictionary—if it is listed with a hyphen, there’s a good chance that it always takes one regardless of its position.
A compound noun is a noun composed of two or more words that work together as a single unit to identify a person, place, or thing.
Writing compound nouns is a bit complicated due to the fact that they can take three different forms: open (or spaced), hyphenated, and closed (written as a single word). Unfortunately, there aren’t any rules that tell us which of the three forms is acceptable for a particular compound noun. Here are some examples of hyphenated compound nouns:
- six-pack (quantifier + noun)
- check-in (noun + preposition)
- mother-in-law (noun + preposition + noun)
- eight-year-old (number + noun + adjective)
Single-word compound verbs
We sometimes use other parts of speech, especially nouns and adjectives, to form verbs that describe a very specific action. When these are combined into a single word, we often use a hyphen to eliminate possible confusion when reading. For example:
- “Why don’t we go ice-skating this weekend?”
- “Please be sure to double-space your essays.”
- “After the horrible heatwave last year, the campus has promised to start air-conditioning their classrooms.”
- “I would like to test-drive the car before I buy it.”
However, as certain words become more commonplace, they tend to lose their hyphenation. For instance:
- “We need to childproof the house this weekend.”
- “I’m going to babysit for them next Friday.”
- “The report still needs to be copyedited, but otherwise it’s finished.”
If you’re unsure whether to hyphenate a single-word compound verb, check the spelling in a good dictionary.
Usage Note: Compound verbs vs. Compound predicates
A compound verb is one that is formed from two or more words. In addition to the single-word compound verbs that we just looked at, there are also phrasal verbs and prepositional verbs. Verbs formed using auxiliary verbs are also sometimes referred to as a type of compound, since there are composed of multiple verbs. (Note that only single-word compounds are hyphenated.) For example:
- “I don’t mean to second-guess you, but you should check the work again.” (single-word compound)
- “We’re just waiting for the plane to take off.” (phrasal verb)
- “Kelly asked for a raise.” (prepositional verb)
- “I will see him on Monday.” (auxiliary verb construction)
Be careful not to confuse compound verbs with compound predicates, which refer to multiple actions being performed by the same subject of a clause. Compound predicates are made up of multiple verbs joined by a conjunction (and a comma or commas, if there are more than two). For example:
- “By the time she was five, she could read, write, and play the violin.”
Note that you may find sources that erroneously call these compound verbs, but this is not correct.
While we usually write double-digit numbers numerically (as in 21, 45, 87, etc.), we can also write them as words. For any double-digit number higher than 20 and lower than 100, we use a hyphen to write it as a compound number.
- twenty-one (21)
- forty-five (45)
- eighty-seven (87)
We use this same method if the hyphenated number appears in a compound that’s more than two digits. If the number has more than three digits, we use commas in the same way as we would for writing it numerically. For example:
- one hundred ninety-nine (199)
- two thousand, three hundred thirty-two (2,332)
- five million, four hundred fifty-six thousand, one hundred twenty-two (5,456,122)
This will also work the same way when we write full years (we don’t use commas for these):
- “The United States declared its independence in seventeen seventy-six .”
- “The fifty-third [53rd] US presidential election took place in nineteen ninety-six .”
Similar to how we form compound numbers, we also use a hyphen when we write fractions. For example:
- “The auditorium was only one-third (1/3) full.”
- “We’ve still got three-quarters (3/4) of a tank of gas.”
Forming compound words with prefixes
A prefix attaches to the beginning of a word (known as the root or stem word) to change its meaning.
The vast majority of prefixes don’t require a hyphen when they are attached to the root. Here are just a few examples:
- un + happy = unhappy (not happy)
- de + activate = deactivate (turn off or stop from functioning)
- semi + circle = semicircle (half a circle)
However, it is sometimes the case that adding a prefix to a stem can result in a word that is hard to read. In this case, we can use a hyphen between the prefix and the stem word to clarify the meaning of the new word.
Many writers choose to add a hyphen when the last letter of the prefix and the first letter of the root are both the same (usually vowels) so as to avoid creating a word that is difficult or confusing to read. For example:
- co + operate = co-operate (work/operate together)
- re + election = re-election (a second election)
Note that this hyphen is often optional and up to the writer’s discretion, and many double-vowel words are now commonly spelled without the hyphen. If in doubt, use a good dictionary or check your school’s or business’s style guide.
Another instance when we might use a hyphen is when the resulting spelling would be confusing or awkward to read. For example:
- co + edit = co-edit (compare with coedit)
- de + ice = de-ice (compare with deice)
Again, using the prefix without a hyphen is often a correct way to spell the word too, so the hyphen is purely up to the writer’s discretion.
Creating words with a different meaning
When adding a prefix (especially re-) creates a word that looks the same as (or similar to) an existing word with a different meaning, we should use a hyphen to avoid confusion. For example:
- re + cover = re-cover (meaning “to cover again”; compare with recover, meaning “to get back or regain”)
- de + stress = de-stress (meaning “to reduce stress”; without the hyphen, destress looks very similar to distress, meaning “to cause strain, anxiety, or suffering”)
With proper nouns and adjectives
When a prefix is paired with a proper noun or a proper adjective, we use a hyphen so we don’t have a capital letter appearing in the middle of a word. While hyphens have been almost always optional in our previous examples, we always use a hyphen with proper words. For example:
- pro + Canada = pro-Canada (in favor of Canada; not proCanada)
- pre + Industrial Revolution = pre-Industrial Revolution (before the beginning of the Industrial revolution; not preIndustrial Revolution)
Note that some style guides suggest using an en dash ( – ) instead of a hyphen when a prefix is used with a proper noun or adjective that is already a compound, as in our last example. Using this method, it would look like this:
- pre–Industrial Revolution
However, this is largely a personal preference, unless the style guide used by your school or employer specifically prescribes its use.
(See the usage note at the end of this section for more information on using en dashes vs. hyphens.)
With self-, all-, and ex-
In addition to proper nouns and adjectives, we almost always use a hyphen with the three prefixes self-, all-, and ex-, as in:
- self + conscious = self-conscious (not selfconscious)
- all + encompassing = all-encompassing (not allencompassing)
- ex + boyfriend = ex-boyfriend (not exboyfriend)
The hanging hyphen
Sometimes the same word will be repeated in multiple consecutive compound words. Rather than just repeat the word multiple times, which would lead to a repetitive sentence, we use what’s known as a hanging hyphen (also called a suspended hyphen, suspensive hyphen, dangling hyphen, or floating hyphen). This is the only instance in which a hyphen can be followed (or preceded) by a space.
Usually, it is the last word (or words) in a compound that will be omitted and leave a hyphen “hanging” from the end of a descriptor in the compound. For example:
- “There are many interesting differences in the way social classes operated in pre- and post-war Britain.”
- “My dissertation is going to focus on late-nineteenth- and early-twentieth-century literature.”
- “I teach sixth-, seventh-, and eighth-grade students.”
- “My mother- and father-in-law are flying in from Chicago this evening.”
- “Each politician must ask him- or herself what is best for the country.”
(Note that, as in the last example, a hanging hyphen can be used for a closed compound word that would normally not use a hyphen.)
Much less commonly, the first word of a compound is omitted, which means the hyphen is suspended from the beginning of the compound’s descriptor, as in:
- “We’re here today to honor the policemen and -women who go above and beyond the call of duty.”
- “The family-owned and -operated business has been a part of the local community for over 50 years.”
Aside from the grammatical function of forming compounds, the hyphen is also used for two technical purposes.
Dividing numerical sequences
When we have long numerical sequences that are not representative of a sum, we often use hyphens to separate them into smaller sections that are easier to read. This is often used for telephone numbers or unique personal identifiers.
Expressing a range of values
Hyphens are often used to indicate a range of values, usually numbers or dates. For example:
- “Please refer to pages 83-88 for more information.”
- “The clinic is open Monday-Friday, 8:00 AM-5:00 PM.”
They can also be used when reporting the result of a ballot or score of a contest, as in:
- “The home team beat their rivals 10-2 in the homecoming game.”
- “The board voted 5-4 to accept the proposal.”
However, many style guides—including this one—recommend using an en-dash instead of a hyphen in such instances.
Usage Note: Hyphens vs. Dashes
It’s important to clarify the difference between hyphens and dashes. Although they are very similar in appearance, they have very different grammatical functions.
As we said already, hyphens are used to join words or sets of numbers together to form a single unit.
Dashes are subdivided into two types: en dashes (–) and em dashes (—). En dashes are slightly longer than hyphens (approximately the width of a capital N), while em dashes are slightly longer than en dashes (approximately the width of a capital M).
En dashes are the preferred punctuation used to either express a range (usually of numbers or dates) or the result of a contest or vote. Let’s look at our previous examples, this time using en dashes instead of hyphens:
Em dashes (often simply referred to as dashes, because they are more common) are used to indicate parenthetical information or to emphasize a part of a sentence. They are used in pairs if the information appears in the middle of a sentence, but only one is used if the information appears at the end of the sentence. For example:
It is quite common to see a hyphen used in place of dashes (usually because it is simply faster and easier to type), but this should be avoided, especially for em dashes. Using hyphens for too many purposes can result in a very confusing sentence. However, if you do use hyphens instead of em dashes (for instance, if you are using a typewriter and cannot form an em dash), just use two hyphens in a row, as in:
For more information on using en and em dashes, see the chapter on Dashes.