A. Hyphens are used to connect words that are more closely linked to each other than to the surrounding syntax. Unfortunately their use is not consistent. Some pairs or groups of words are written as a single word (e.g. motorway, railwayman), others, despite their equally close bond, as separate words (e.g. motor cycle, pay phone); very similar pairs may be found with a hyphen (e.g. motor-cyclist, pay-bed). There are no hard and fast rules that will predict in every case whether a group of words should be written as one, with a hyphen, or separately. Useful lists can be found in Hart's Rules for Compositors and Readers, (edn. 39) Oxford 1983, pp. 76-81; numerous individual items are entered in The Oxford Dictionary for Writers and Editors, Oxford, 1981.

1. Groups consisting of attributive noun + noun are probably the most unpredictable. It is the nature of English syntax to produce limitless numbers of groups of this kind. Such a group generally remains written as separate words until it is recognized as a lexical item with a special meaning, when it may receive a hyphen. Eventually it may be written as one word, but this usually happens when the two nouns are monosyllabic and there is no clash between the final letter of the first and the first letter of the second. This generalization is, however, a very weak guide to what happens in practice. Compare, for example,

coal tar, coal-face, coalfield; oil well, oil-painting, oilfield; blood cell, blood-pressure, bloodstream.

2. Nouns derived from phrasal verbs, consisting of verb + adverb, are slightly more predictable. They are never written as two words, frequently hyphened, and sometimes written as one, e.g.

fall-out, play-off, set-back, turn-oat, feedback, layout, runoff, turnover.

Phrases consisting of agent-noun in -er + adverb are usually hyphened, e.g.

picker-up, runner-up;

those consisting of gerund in -ing + adverb are usually left as two words, e.g.

Your coming back so soon surprised me,

unless they have become a unit with a special meaning, e.g.

Gave him a going-over.

3. Various collocations which are not hyphened when they play their normal part in the sentence are given hyphens when they are transferred to attributive position before a noun, e.g.

(a) adjective + noun:

a common-sense argument (but This is common sense),
an open-air restaurant (but eating in the open air).

(b) preposition + noun:

an out-of-date aircraft (but This is out of date),
an in-depth interview (but interviewing him in depth).

(c) participle + adverb:

The longed-for departure
and
Tugged-at leaves and whirling branches (Iris Murdoch)
(but
the departure greatly longed for;
leaves tugged at by the wind).

(d) other syntactic groups used attributively,

e.g. A tremendous wrapping-up-and-throwing-away gesture (J. B. Priestley); An all-but-unbearable mixture (Lynne Reid Banks).

4. Collocations of adverb + adjective (or participle) are usually written as two words when attributive as well as when predicative, e.g.

a less interesting topic, an amazingly good performance,

but may very occasionally take a hyphen to avoid misunderstanding, e.g.

Sir Edgar, who had heard one or two more-sophisticated rumours (Angus Wilson)

(this does not mean 'one or two additional sophisticated rumours').

well is joined by a hyphen to a following participle when the combination is used attributively, e.g.

A well-worn argument.

Predicatively a hyphen is not necessary unless the combination is to be distinguished in meaning from the two words written separately, e.g.

He is well-spoken
but
The words were well spoken.

5. When two words that form a close collocation but are not normally joined by a hyphen enter into combination with another word that requires a hyphen; it may be necessary to join them with a hyphen as well in order to avoid an awkward or even absurd result, e.g. natural gas needs no hyphen in natural gas pipeline, but natural-gas-producer may be preferred to the ambiguous natural gas-producer; crushed ice + -making looks odd in crushed ice-making machine, and so crushed-ice-making machine may be preferred. Occasionally a real distinction in meaning may be indicated, e.g.

The non-German-speakers at the conference used interpreters
versus
The non-German speakers at the conference were all Austrians.

Many people, however, prefer to avoid the use of long series of hyphened words.

6. A group of words that has been turned into a syntactic unit, often behaving as a different part of speech from the words of which it is composed, normally has hyphens, e.g.

court-martial (verb),
happy-go-lucky (adjective),
good-for-nothing,
stick-in-the-mud,
n'er-do-well (nouns).

7. A hyphen is used to indicate a common second element in all but the last word of a list, e.g.

two-, three-, or fourfold.

Hyphens within the word