Hyphens and dashes

Hyphens (-)

Hyphens are used to join words together. Some common use of hyphens can be found in:

  • compound words
  • prefixes
  • adjectival phrases also known as compound adjectives
  • compass directions
  • numbers (not sure if needed since we use numerals for bigger numbers?)

Best practices

  • 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 - 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

Supporting studies

It is hard to envisage a usability study which would help us determine the efficiency or otherwise of hyphens. The references below provide sensible guides on clarity and consistency.

Dashes

Dashes are used as punctuation in sentences and in numeric copy..
There are two types of dashes:

  • En-dash
  • Em-dash

En-dashes (–)

The en-dash is:

  • wider than a hyphen, but narrower than an em-dash
  • the same length as the letter ‘n’
  • in a sentence, most commonly used – like this – in place of commas to separate out a parenthetical phrase
  • used for ranges of numbers (scores, votes, or contest results)

To produce an en-dash:
PC

  • press and hod the ALT key and type 0150 on the numeric keypad
  • only the numbers on the right hand keypad do this, not the numbers above the letters

Mac

  • press Option and the minus key simultaneously

Best practices

  • should always have a space before and after if used in a middle of a sentence
  • do not have spacing if used with numbers.

Examples

  • World War l (1914–1918)
  • 2001–
  • pages 32–85
  • L5–S1 disc herniation
  • Blue Jays win 4–2 in the eleventh inning

Supporting studies

Em-dashes (—)

The em-dash is:

  • much wider than the hyphen and the en-dash
  • the same 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.

To produce an em-dash:
PC

  • press and hod the ALT key and type 0151 on the numeric keypad
  • only the numbers on the right hand keypad do this, not the numbers above the letters

Mac

  • press Shift, Option and the minus key simultaneously

Best practices

  • should never have spacing before and after
  • avoid using an em-dash if you can replace it with a comma or parentheses

Examples

  • My favorite ice-cream flavours—vanilla, strawberry and chocolate
  • The prime minister—who recently came back from a visit to the UK—announced that he is looking forward to the trade collaboration

Supporting studies

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