You might wonder what the difference is between hyphens (-) and dashes/rules (*– en, — em dash/rule) that are to be seen in publications. Well, they have distinct functions in punctuation. The main ones are covered below.
These are used
- to join two words together (e.g. ‘mother-in-law’, ‘ill-natured child’), called a hard hyphen
- to indicate a word division at the end of a line, called a soft hyphen
- to indicate a missing element, called a floating hyphen (e.g. ‘over- and under-paid’, ‘pre- and post-war history’, ‘seventeenth- and eighteenth-century architecture’).
Pairs of words go through three stages of being used together: for example, initially coal field, then through increased use to coal-field, and finally through widespread use to coalfield.
Hyphens are meant to assist in comprehension, as in ‘a big boat captain’. Is it the boat or captain that is big? For clarity you would hyphenate as ‘a big-boat captain’ to indicate he is the captain of a big boat, rather than a tall or rather portly captain (eaten too many pies perhaps). Other examples would be a ‘black-bearded man’ or ‘deep-blue sea’.
The current trend is to use hyphens sparingly and in the occasions mentioned in the previous paragraph, using them only to avoid ambiguity and confusion. American authors tend to use fewer hyphens than their British counterparts.
En dashes (–)
This is a dash or rule that is longer than the hyphen that can be used as follows:
- unspaced in number spans to replace the word ‘to’, such as pages 236–54, 492–6 (often in these cases minimum numerals are used – referred to as elision)
- unspaced between two items that are linked but not joined in a fixed sense, such as in the London–Birmingham railway
- spaced to indicate a parenthetical clause, such as in ‘The party lasted – as we all knew it would – well into the early morning’. (Note that no punctuation should normally precede a single dash or the opening one of a pair.)
Em dashes (—)
This dash is longer than the en dash above and can be used as follows:
- parenthetically for clauses in the same way that en dashes are used above, a practice often adopted in US English texts and some UK journals, but where they are often unspaced (no space before or after them)
- in dialogue to indicate an interruption ‘I warned him not to—’
- as two together, i.e. ——, to indicate a repeated author’s name in bibliographic entries.
(*Note the terms ‘en’ or ‘em’ refer to a printer’s measure.)