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 Hyphens
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Carlos Cajina from Nicaragua asks:

Compound adjectives can be: 1. Joined by a hyphen 2. Appear as a single word 3. Appear as two separate words. Is there a rule - or set of rules - to know when to use any of the three alternatives described above?

Imran Munir from Pakistan asks:

Could you please underline the common pitfalls related to hyphen usage in English?

 
Roger replies:

You'll find the hyphen used in compound nouns, in compound adjectives and in prefixes.

Compound nouns

Most compound nouns are normally written as two separate words, although it is not a hard-and-fast rule:

hyphen usage, swimming pool, driving licence, human being, contact lens, news bulletin

The most common compound nouns which are normally linked with a hyphen include:

passer-by
dry-cleaning
x-ray
mother-in-law (etc)
do-it-yourself (D-I-Y)
turn-over
parent-teacher association
pen-friend
t-shirt

When compound nouns function as adjectives, they are normally hyphenated. Compare the following:

  • 'The afternoon was so hot that I decided to go to the open-air swimming pool. I love to eat in the open air in the summer.'

  • 'Air traffic was so dense that afternoon that air-traffic control could hardly cope.

Compound adjectives

Most compound adjectives are made up of two, or sometimes three, words and are usually written with a hyphen between them. Here are some compound qualitative adjectives with nounsthat they typically collocate with:

a clear-cut decision
a far-fetched explanation
a low-cut dress
a light-hearted argument
a free-and-easy relationship
an old-fashioned haircut
an off-hand remark
cold-blooded murder

 

Here are some compound classifying adjectives with nouns that they typically collocate with:

a last minute decision
an all-out effort
a cross-country bus
cut-price bargains
full-time staff
strong-arm tactics
worn-out tyres
a deep-sea diver

 

And here are a few compound colour adjectives with nouns that they typically collocate with:

a jet-black sky
snow-white boots
flesh-coloured swimming trunks

Note that although compound adjectives are written with hyphens when they appear before nouns, they are usually written without hyphens when they are used as complements of the verb.

Compare the following:

  • 'The products on the shelves were out of date and had to be withdrawn.'

  • 'His out-of-date argument gathered little support.'

  • 'Out-of-work policemen often find employment as security guards, but it is not so easy for teachers who are out of work to find other jobs.'

Prefixes

The prefixes co-, non- and ex- are sometimes separated from the following noun, adjective or verb by a hyphen:

  • 'His co-operation in the co-production was much appreciated.'

  • 'He co-ordinated the election in which Hilary Jenkins was co-opted as a member of the committee.'

  • 'Non-alignment does not always imply non-involvement in the affairs of a neighbouring country.'

  • 'Non-profit-making organisations are non-existent in this country.'