Hyphens and dashes

Recommendations

Hyphens

Hyphens are used to join words, like compound words, prefixes and compass directions, together.

  • do not use a hyphen unless the word is confusing without it
  • never add white spaces at both ends
  • avoid using hyphens for time and date ranges, instead use "to"

Hyphens in compound words tend to disappear over time if the compound becomes widely used. Inter-networking became inter-net became internet. Coffee-maker is now often coffeemaker, brides-maid is bridesmaid. Consistency within a document or an organisation is probably more important than 'correctness'.

The same words will have hyphens when used as a compound adjective before a noun but not if they come after it. For example, first-class essay but the essay is first class. This is mainly to avoid ambiguity: the Oxford reference below says 'For example, 250-year-old trees clearly refers to trees that are 250 years old, while 250 year old trees could equally refer to 250 trees that are all one year old'.

Hyphens in prefixes have also tended to decline in recent years, so it's common to see colocate rather than co-locate, deregulate rather than de-regulate. Sometimes a hyphen is needed for clarity (re-cover and recover, coop and co-op).

Examples

  • x-ray, full-time
  • de-classify, post-war
  • north-east, south-west
  • thirty-four, sixty-seven

Dashes

Dashes are sometimes used as punctuation in sentences. There are two types, the en-dash and the em-dash. Avoid using an en-dash or an em-dash if you can replace it with commas or brackets.

The en-dash (–) is:

  • wider than a hyphen, but narrower than an em-dash
  • the length as the letter ‘n’

En-dashes should always have a space before and after if used in the middle of a sentence.

The em-dash (—) is:

  • wider than the hyphen and the en-dash
  • the length as the letter ‘m’
  • very unusual in UK-English text: US-English uses an unspaced em-dash as a separator in text in places where UK writers would use a spaced en-dash.

Em-dashes should never have spacing before and after.

Usability evidence

'The Trouble With EM ’n EN (and Other Shady Characters)', 2001

Oxford Living Dictionaries 'hyphen' entry, 2010

"Does hyphenation increase readability?" 2012

The hyphen, University of Sussex, 2013

The dash, University of Sussex, 2013

'Why Don’t Screen Readers Always Read What’s on the Screen? Part 1: Punctuation and Typographic Symbols', 2014

'Hyphens or en dashes—which are more readable when used in number ranges (for North American web users)?', 2014

'Perilous Punctuation: Use the Dash With Panache', 2015

Oxford Living Dictionaries 'em dash' entry, 2018

Hyphens dashes readability Google Scholar search results Google Scholar, October 2018

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