Hyphens and Dashes
A hyphen joins two or more words together (e.g. x-ray, door-to-door) while a dash separates words into parenthetical statements (e.g. She was trapped - no escape was possible.
Generally, hyphens are used to avoid confusion or ambiguity but today most words that have been hyphenated quite quickly drop the hyphen and become a single word (e.g. e-mail and email, now-a-days and nowadays). In many cases though a hyphen does make the sense clear:
- I am thinking of re-covering my sofa (to put a new cover on it)
- I would like to recover my sofa. (perhaps from someone who has borrowed it as this means 'to get it back')
Hyphens and numbers
1. Use a hyphen with compound numbers from twenty-one to ninety-nine.
2. In written fractions place a hyphen between the numerator and denominator.
[Exception] if there is already a hyphen in either the numerator or the denominator, you omit the hyphen between the numerator and denominator.
- sixty-nine eighty-ninths (not 'sixty-nine-eighty-ninths')
- twenty-two thirty-thirds
3. Use a hyphen when the number forms part of an adjectival compund:
- France has a 35-hour working week.
- He won the 100-metre sprint.
- Charles Dickens was a great nineteenth-century novelist.
UsageConsult your dictionary if you are not sure but remember that current usage may be more up-to-date (not uptodate... yet!) than your dictionary. There are some cases where hyphens preserve written clarity such as where there are letter collisions (co-operate, bell-like) or where a prefix is added (anti-nuclear, post-colonial), or in family relations (great-grandmother, son-in-law.)
Dashes can be used to add parenthetical statements in much the same way as you would use brackets. In formal writing you should use the bracket rather than the dash as a dash is considered less formal in most cases. However, they should not be overused nor used to replace commas although they can be used to create emphasis in a sentence.
- You may think she is a liar - she isn't.