Use hyphens to link words for clarity
Hyphens glue words together so the reader knows they are linked.
Some of the rules for using hyphens are straightforward, but there are several exceptions and often you have to decide whether a hyphen is necessary. That is why some people dislike hyphens and probably why the Oxford University Press style manual says:
‘If you take hyphens seriously, you will surely go mad.’
Used to create a single concept
One of the most common uses of a hyphen is to link two or more words that modify the following noun. The hyphenated words act as a single concept and are sometimes called a compound adjective.
You don’t usually need a hyphen when the descriptive concept comes after the noun.
the employee works full time
If a phrase consists of an adverb, adjective and noun, it is usually not hyphenated because the adverb is modifying the adjective rather than the words acting as a single concept.
a very good meal (adverb, adjective, noun)
However, to complicate matters, hyphens are used with some adverbs including better, best, ill, least, little, most, much, worse, worst and well if they are followed by the past tense of the verb.
Used to create new words
Hyphens are often used when new words are invented out of existing words. Many of these hyphens drop out over time.
web site, web-site, website
Used in common expressions
Hyphens creep into some commonly used expressions.
Used with numbers
Hyphenate numbers, fractions and ages.
Used with single letters
Hyphens are often used when a single letter is added to the front of a word to make a new word, though many e-words now drop the hyphen.
e-mail (now usually email)
Used with some prefixes
Use a hyphen:
- If the word that follows the prefix starts with the same vowel, though some double vowel usages have now become accepted
de-emphasise, but coordinate
- For the prefixes quasi-, all-, ex– and self-
- To join a prefix to a proper noun
- Between a prefix and a date
- To avoid ambiguity
re-form and reform
Used in some suffixes
Hyphens are generally not used with suffixes (threefold), but you need them occasionally for clarity. Hyphens are often used with the suffixes –elect, -like and -wise.
We hyphenate words that act as a unit to describe the following word.
Two year old describes the age of the child, so you would write two-year-old child.
No hyphen with y and ly adverbs
The rules around using hyphens with adverbs are not clear cut. The basic rule is that a descriptive phrase consisting of an adverb ending in y or ly and an adjective are not hyphenated.
The rationale is that the adverb is modifying the adjective, rather than the two words acting as a single unit.
a very good meal
rapidly declining dollar
gently rocking cradle
highly likely outcome
easily defeated vote
It is common to see other adverbs hyphenated.
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