The hyphen is often regarded as an unnecessary punctuation mark, but I think it’s quite useful because it can provide clarity and prevent ambiguity. The challenge is to use your commonsense, avoid over-hyphenating and hyphenate consistently.
Compare the following words and phrases.
re-sign, resign
more-important arguments (higher priority), more important arguments (additional)
three-monthly tax statements (every three months), three monthly tax statements (monthly)
Hyphens form new words
Hyphens are often used when new words are invented out of existing words. These hyphens often drop out over time.
web site, web-site, website
Some hyphens with prefixes also drop out over time. Your dictionary is a good guide for such hyphen usage.
co-ordinate has become coordinate
semi-colons are now called semicolons
Hyphens are often used initially in compound words, consisting of two or more words that together carry a new meaning. These hyphens often drop out.
take over, take-over, takeover
time frame, time-frame, timeframe
Hyphens create single concepts
The most common use of hyphens is to indicate that two or more words are acting as a single concept to describe the following noun.
full-time employee
hard-working employee
four-wheel-drive vehicle
We don’t use hyphens when the descriptive words follow the noun.
The employee works full time.
The employee is hard working.
However, this rule is not applied consistently, because we tend not to use hyphens for phrases that are commonly used and not ambiguous.
income tax return
secondary school teacher
climate change scenarios
Suspended hyphens
When you have two phrases in a sentence that would both take a hyphen if the noun were repeated, you have to decide whether or not to use a suspended hyphen. I think it is unnecessary and ugly, but it is commonly used.
All the part- and full-time workers went on strike.
All the part and full-time workers went on strike.
Commonly used phrases
Words that are commonly used together attract hyphens to show their relatedness even when they are not followed by a noun.
The area was drought-stricken.
The effects were far-reaching.
bitter-sweet
mother-in-law
Hyphens with adverbs
The rules around using hyphens with adverbs are not clear cut.
No hyphen with y and ly adverbs
The basic rule is that a descriptive phrase consisting of an adverb and an adjective is not usually hyphenated. Most of the adverbs that aren’t hyphenated end in y or ly, though there are a few others, such as quite.
The rationale is that the adverb is modifying the following word, usually an adjective, rather than the two words acting as a single unit.
a very good meal
rapidly declining dollar
Many writers flout this rule if they want to show a close relationship between the two words. I see such unnecessary hyphens in newspapers quite often.
intensely-debated legislation
legally-binding document
Hyphens with adverbs and past participles
Use a hyphen with the adverbs better, best, ill, least, little, most, much, worse, worst and well, if they are followed by a past participle and describe the following noun.
best-kept secret
little-known actor
Hyphens with prefixes and suffixes
Prefixes
Use hyphens if the following word starts with the same vowel.
de-emphasise
co-opt
However, some double vowel usages have now become accepted.
coordinate
cooperate
You can also use a hyphen if the word following has a different vowel, but would look and sound odd.
de-ice
Quasi-, self-, all- and ex- generally take hyphens.
quasi-official
self-effacing
all-embracing ex-director
We use hyphens to join a prefix to a proper noun.
pro-American
We use a hyphen between a prefix and a date.
pre-1950
We also use hyphens to avoid ambiguity.
re-form, reform
Suffixes
Hyphens are generally not used with suffixes.
threefold
knockout
pushover
But you need them occasionally for clarity. Hyphens are often used with suffixes, such as –able, -elect,
-like and -wise.
President-elect
money-wise
Hyphens with single letters
Hyphens are used with single letters, but many e-words now drop the hyphen.
X-ray
H-bomb
Splitting words
Designers sometimes put hyphen breaks in long words at the end of sentences in print documents. When you’re checking your designers’ work, you need to make sure they have split words at the end of a syllable.
syll-able
mult-iple
With numbers
Hyphenate fractions and numbers when they are written in full.
three-tenths
twenty-five people
Want to learn more about punctuation? Why not do Mary Morel’s online writing course: An A to Z of Punctuation?