Grammar: The Dash [ – ]


Alone among punctuation marks, the increasingly popular dash1 is never grammatically required, whether singly or in pairs; there is always an
option.


The Single Dash

The single dash is normally a feature of informal English and is used, especially in narrative, to create suspense or to indicate that what follows is
an afterthought or something to be emphasised –

      There is was again, that creak on the staircase. Pamela sat upright in
      bed, eyes wide open in the darkness. Just Marmalade her cat, she
      thought – or was it?

A comma in place of the dash here, although correct, would fail to achieve the required tension. On the other hand, a sentence fragment, Or was it?
might be used with the same effect.

A single dash may also be used (as in this sentence) in place of a colon to announce an elaboration, example or moral –

      That a £5m lottery winner could become destitute after just four years 
      bears testimony to the old adage – a fool and his money are soon parted.

To indicate an unfinished sentence in quoted speech, three dots are used if the sentence is deliberately left unfinished by the speaker –

      ‘If he talks to me like that once more, so help me I’ll…’

but an unspaced dash is preferred if it is left unfinished for reasons beyond the speaker’s control –

      Don’t worry, boys; they couldnt hit an elephant at this dist–2

Finally, the single dash, again with no intervening space, is used to span calendar years (2011–12), page numbers (pp. 171–75), place names 

(Oxford–Cambridge Boat Race) and symbols (A–Z of London). But note that the hyphen, not the dash, is used with compound words and 
numbers: a one-year contract; a
twenty-six-year-old man.

 

The Double Dash

The double dash encloses supplementary information in the same way as round brackets

      Alaska – purchased from Russia in 1867 and granted statehood in
      1959 – comprises some 586,000 square miles and 624,000 people.

But brackets are preferred in formal scripts.

The double dash can also replace isolating commas to create emphasis –

      I object most strongly to taxpayers’ money – my money – being used
      in this way.

      She said – and I heard her quite clearly – that she would meet me outside
      the station at ten.

 

____________

1 The dash [  ] should not be confused with the shorter hyphen [ - ]. The dash usually separates words; the hyphen connects them. In Microsoft 
   Works, the en dash [ 
– ] and em dash [ — ] are created from the Special Character option in the Insert menu. The en dash is the more common
   of the two.

2  Reputedly the last words of General John Sedwick of the Union Army who was killed by a Confederate sniper at the Battle of Spotsylvania Court
   House in 1864. Q
uoted from R. L. Trask, The Penguin Guide to Punctuation, Penguin Books, London, 1997, p. 70.