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How to use hyphens in academic writing

9th June 2020 blog

Cheat sheet

No time to read? Here’s the short version:

  • Hyphens are punctuation marks used to link multiple words.
  • Use a hyphen to join words together to avoid ambiguity.
  • Use a hyphen when two or more words act as a single adjective before a noun.
  • Hyphenate spelled-out numbers between 21 and 99 (twenty-one, ninety-nine).
  • Hyphenate phrasal verbs (Why did he hold up traffic?) used as nouns (What’s the hold-up?).
  • Some prefixes and suffixes require hyphens, while others don’t; it’s always a good idea to consult a dictionary.
  • Use suspended hyphens to shorten lists of compound adjectives (I bought wood-, window-, and tile-cleaning products).
  • Use a dash (not a hyphen) to separate parts of a sentence and in number ranges.

What’s a hyphen?

A hyphen (-) is a punctuation mark used to join words or parts of words.

load-bearing wall

pre-existing condition

well-known scholar

mother-in-law

twentieth-century literature

Why are hyphens important?

Hyphens are used to join words so as to express an idea more efficiently or to clarify words or phrases that might be confusing on their own.

For example, the phrase a man-eating tiger is tidier and more succinct than a tiger known to eat human flesh.

A hyphen can completely change the meaning of a phrase. Consider the difference between the employee resigned and the employee re-signed. The first means that the employee quit her job, whereas the second means exactly the opposite—that she renewed her employment contract.

Some phrases are ambiguous without a hyphen. Take, for example, the phrase twelve year old girls. Unhyphenated, it’s confusing because it could mean either of the following:

twelve-year-old girls (an unspecified number of girls, each aged 12)

twelve year-old girls (exactly 12 girls, each of whom is one year old)

Hyphens are therefore necessary in a variety of scenarios:

  • When using multi-word adjectives (known as compound adjectives)
  • To spell out certain numbers or numerical phrases
  • When using phrasal verbs as nouns (hold-up, break-in)
  • When a list includes broken words (e.g., oil- and water-based colours)
  • With certain prefixes and suffixes

Compound adjectives

In the following phrases, two or three words have been joined together with hyphens to create a compound adjective that describes the noun that follows.

the soft-spoken professor

around-the-clock service

low-interest savings account

Careful, though! Only hyphenate compound adjectives that come before a noun. If the description comes after the noun, the hyphen is usually not necessary.

Description before nounDescription after noun
A well-respected mathematician developed the algorithm.A mathematician who is well respected in her field developed the algorithm.
The technician’s in-depth knowledge of the electrical system allowed him to carry out the repair quickly.The technician knew the electrical system in depth, so he was able to carry out the repair quickly.
The centuries-old tradition of fasting on Good Friday is rarely followed today.The tradition of fasting on Good Friday is centuries old, but it is rarely followed today.
After a three-year drought, Cape Town’s water reserves were critically low.After a drought of three years, Cape Town’s water reserves were critically low.

Not sure whether a phrase is a compound adjective? Try replacing the phrase with the word awesome. If the sentence makes sense with the replacement, then it is a compound adjective and you need a hyphen. If the sentence no longer makes sense, then the phrase is likely a noun phrase, and no hyphen is needed.

No hyphen in compound adjectives with -ly adverbs

Compound adjectives that contain an adverb ending in -ly do not need a hyphen. (Remember: adverbs describe verbs, adjectives, or other adverbs and answer the question ‘How?’)

The highly contagious virus spread rapidly.

The interns competed for the extremely prestigious position.

The actor remained largely unknown until late in his career.

The results were skewed by poorly calibrated equipment.

Suspended hyphens

To avoid wordiness, hyphens are also used to stand for a common second element in a list of compound adjectives in all but the last word of the list.

The government’s pre- and post-war policies on taxation differed markedly.

The new skyscraper featured a combination of Eastern- and Western-style architectural elements.

The Cubist style influenced both 20th- and 21st-century artists.

Occasionally, suspended hyphens can also replace the first element in a list of hyphenated compound adjectives.

The new franchise is investor-owned and -operated.

When to hyphenate numbers

Many academic style guides suggest using numerals for numbers above 10, unless they start a sentence. If you do decide to spell out numbers, remember that most numbers from 21 to 99 require a hyphen (the exceptions are, of course, all multiples of ten, e.g. thirty, forty).

The control group included seventy-six patients.

Presidential candidates must be at least thirty-five years old.

If the first word of a compound adjective is a number or a fraction, use a hyphen. This rule applies whether the number is represented by numerals or spelled out in words.

The pastor gave a thirty-minute sermon.

Our basketball team had a 20-point lead by halftime.

Always use a hyphen for centuries if they are adjectives before nouns.

All invitees were asked to attend the party in 18th-century costume.

Eighteenth-century architecture saw a revival of the classical style.

A hyphen is not required when a number is the last part of a compound adjective.

He suffers from type 2 diabetes.

Access to classified information requires a Level 4 security clearance.

Phrasal verbs used as nouns

A phrasal verb is a combination of a main verb and one or more other words (usually an adverb or a preposition) that produces a special meaning. Phrasal verbs do not typically need hyphens. However, phrasal verbs often have corresponding noun forms that do require hyphenation.

Phrasal verbPhrasal noun
He broke up with his girlfriend.He has been struggling since the break-up.
The government bailed out the banking industry.The government bail-out of the banking industry attracted criticism.
Heavy snow caused traffic to build up on the motorway.Heavy snow caused a build-up of traffic on the motorway.

Many phrasal verbs are too informal or wordy for academic writing, so remember to replace them with one-word alternatives whenever possible.

When to hyphenate prefixes and suffixes

A prefix or suffix consists of a few letters that can be joined to a word to change its meaning. Prefixes go at the beginning of a word, while suffixes are added at the end.

un + wise    à   unwise

over + qualified  à   overqualified

anti + thesis à   antithesis

romantic + ism    à    romanticism

home + less  à   homeless

child + ish  à   childish

Most prefixes and suffixes do not require a hyphen. However, there are many exceptions, some of which are described below. When in doubt, always consult a reputable dictionary.

Hyphens to separate repeated letters

A hyphen is usually added when applying the prefix or suffix to the root word would result in the same letter being repeated.

anti-isolationist

co-owner

re-elect

shell-like

wiretap-proof

However, there are many exceptions to this general rule. Check your dictionary when using words like the following:

cooperate

coordinate

overreach

overrated

preeminent

Hyphenate proper nouns and proper adjectives

If you use a prefix or suffix with a proper noun or adjective, add a hyphen.

New York-style pizza

pre-Colombian art

a NATO-like alliance

Hyphenate with numbers or single letters

If your phrase uses numbers or a single letter, add a hyphen.

T-shirt

X-ray

post-9/11

Hyphenation with certain prefixes and suffixes

These prefixes always require a hyphen:

PrefixExample
all-

ex- (meaning former)

cross-

self-

an all-encompassing theory

her ex-husband Bill

a cross-referenced entry

upon self-examination

These suffixes always require a hyphen:

SuffixExample
-type

-elect

-based
-free

a skeleton-type key

the president-elect

oil-based paints

duty-free shopping

The suffix -like is hyphenated only if the root word is long (three or more syllables):

childlike

emulsion-like

A hyphen is necessary with the suffix -fold for exact decimals or numbers greater than or equal to 10. For whole numbers below 10, the hyphen is generally omitted.

3.5-fold

20-fold

twofold

If a root word already contains a hyphen, or is actually a multi-word phrase, a hyphen is required when adding a prefix.

Root word Prefix + root word
in their globe-trotting daysin their pre-globe-trotting days
twentieth-century filmmid-twentieth-century film
First World Warpost-First-World-War economic policy

Hyphens vs. dashes

There are two dashes in English punctuation: the en dash (-) and the em dash (—). While these are sometimes confused with hyphens, they operate in very different ways. Hyphens are used exclusively to link words together, but dashes have multiple functions. Both en and em dashes can be used to break up a sentence, usually indicating an aside or a change in tone, thus acting as alternatives to parentheses, commas, or colons. En dashes are also used in number ranges (without the surrounding spaces).

Archimedes’ discovery shows that inspiration can strike anywhere – even the bathtub.

The soldier leapt—or rather limped—over the gate.

Students were assigned the exercises on pages 100–105 as homework.

Need more help?

Any questions? By way of recap, you can have a look at some of the most common hyphenation mistakes our editors have to correct. Then test your newfound knowledge by taking our hyphenation quiz.

If hyphens and dashes are still stumping you, submit your paper for proofreading and let us take care of the punctuation. Get an instant quote on our pricing page.