Hyphen and dash

This section is concerned with the two punctuation marks hyphen (-) and dash (–). Even though they look rather similar, they have different functions, as the rules and examples below are intended to illustrate.

We know that sometimes words contain hyphens. There is considerable variation in this area (that is, not everyone agrees on the proper use of hyphens), but there are a number of cases in which hyphens are used that we must bear in mind. Also always try to be consistent, so that you do not write the same word in different ways in the same text. At the end of a line of writing

• If possible, put the hyphen between two parts of a compound word (eg. motor- at the end of one line and cycle at the beginning of the next one).
• Otherwise, put the hyphen before a suffix (understand -ably, instead of understa -ndably) or after a prefix (mono- transitive, instead of monot- ransitive).
• Words that are not compounds and which do not contain affixes are normally not long enough to have to be divided at the end of a line.

In compounds Generally speaking, compounds can be written in three different ways in English, namely as one word, as two words with a space between them, or with a hyphen between the first and the second part of the word. In many cases, there is variation among writers, and writing conventions change over time, so always consult a recent and trusted dictionary when in doubt. However, the following general rules and advice should be useful: Compound adjectives are often (but not always) written with a hyphen. A compound adjective is typically an adjective that consists of an adjective + a participle (e.g. long-lasting and short-natured), a noun + a participle (thought-provoking and data-driven), or a noun + an adjective (camera-ready, lead-free). It is extra important to use a hyphen when not using one could lead to ambiguity. For instance, we should not write ten year old children if we mean ten-year-old children, since ten year old children could equally well refer to ten children that are one year old (i.e. ten year-old children). Generally speaking, compound premodifying adjectives, that is, adjectives that precede and modify the head of a noun phrase, are more often written with a hyphen than compound adjectives functioning as predicatives. This is especially important to remember when the compound adjective contains the adverb well. For example, even though we could very well write as in (1), we have to use the hyphen in (2):

(1) I find this paper well written. (2) This is really a well-written paper.

Similarly, we have to use hyphens if a premodifying adjective is formed from a phrase (3), even though we may leave out the hyphen when such a compound adjective functions as predicative (4):

(3) A new state-of-the-art laboratory on Deeside marks a big step ahead in Wales' drive for economic renewal and green jobs. (4) This document is part of a series of reviews of the state of the art in cognitive systems.

Compound numbers less than 100 are spellt with a hyphen (e.g. seventy-six, thirty-five).  Phrasal verbs have no hyphens when they are verbs (5), but when they are used as nouns, they get a hyphen, as in (6) below.

(5) Long queues started to build up at these security checkpoints. (6) There was a build-up of fluid in the inner ear, and the doctors drained the fluid out so the child could hear.

After a prefix We insert a hyphen between a prefix and a number or a proper noun (name):

(7) This is a pre-2004 phenomenon. (8) This would reduce the risk of the further deterioration of Iraq into a post-Yugoslavia type of situation.

We also include a hyphen in order to avoid words getting mixed up, so, for instance, we write re-cover, if we do not mean recover, as in (9):

(9) I would like to know how to re-cover dining-room chairs.

It is (or used to be) common practice in British English to insert a hyphen between a prefix ending in a vowel and a word starting with a vowel, as in (10), but this use appears to be losing ground, so we also frequently find such words written as one word without a hyphen, as in (11):

(10) Nato and Russia have made a historic agreement to co-operate over the creation of a missile defence shield protecting more than one billion people in a move aimed at bolstering the “reset” in relations between Moscow and the west. (11) Although the duty to cooperate would render it more difficult for local authorities to refuse a transfer outright, it did not override their discretion when deciding whether this would be compatible with other of their statutory duties or whether they could fulfil the terms of an offender's licence conditions.

There are also a number of prefixes that are always suppused to be followed by a hyphen, for instance all-, cross-, ex-, self-, half-, and anti-, as in (12) to (17):

(12) In principle this could be done by an all-knowing central planner. (13) Cross-Cultural Research (CCR) publishes peer-reviewed articles that describe cross-cultural and comparative studies in all human sciences. (14) After a year or so, my friend and ex-colleague John. Murray VII offered help again. (15) Self-esteem has to do with how one sees and experiences oneself. (16) There is no way anyone in attendance left this show thinking it was half-hearted.  (17) To illustrate what types of behaviour are anti-social, below are examples of ASB.

Finally, please remember the practice of spelling premodifying compunds with hyphens, as illustrated in some of the examples above.

A dash is the punctuation mark – , which is used to separate parts of a sentence. Dashes look like hyphens (which are used, for instance, to connect two or more words, as in a two-year-old child) but are longer. There are two forms of dashes in English language print:

en dash (en rule) – This is the shorter dash, preceded and followed by a blank space (as illustrated). em dash (em rule)—This is the longer, unspaced dash (as illustrated).

Dashes can be used instead of commas to set off a parenthetical element in a sentence:

(1) Driving at night—especially in the rain—can be dangerous and requires more attention than daytime driving.

Note the difference between British and American publishers: most British publishers (except Oxford UP), use the en dash, whereas the em dash with no blank spaces is preferred by most American publishers (and by Oxford UP) (Ritter, 2003, p. 141). In reference lists, the em dash is often used to substitute the author's name if there are several sources by the same author:

Thormählen, M. (2007). The Brontës and Education.  
          Cambridge: Cambridge University Press.
—. (1999). The Brontës and Religion. Cambridge: Cambridge University Press.