7.42 Interruptions, pauses, afterthoughts, clarifications and emphasis

Like parentheses, a dash may be used at the end of an unfinished or interrupted statement or a pause, as in transcripts:

• I have indicated that the appointment of the judge was terminated—or rather was not terminated but came to—
  
  Some Hon. Members: Oh, oh!

Here the dashes are used to indicate, first, a pause and clarification and, second, an interruption.

The dash may be used to introduce an afterthought, correction or repetition:

• Who will oppose—who are now opposed to the union?

It may similarly be used to set off an emphatic ending or one that contrasts with the remainder of the sentence:

• To write imaginatively a man should have—imagination.

Dashes give greater emphasis to parenthetic material than do commas or parentheses. If the parenthetic material contains internal punctuation or forms a complete sentence, the commas that might have been used to enclose it should be replaced by dashes or parentheses, depending on the degree of emphasis desired or the closeness of the relationship to the rest of the sentence. Parentheses are generally used to enclose material more remote from the main thrust of the sentence, dashes for material more closely related:

• This country is something that must be chosen—it is so easy to leave—and if we do choose it we are still choosing a violent duality.
  —Margaret Atwood

The em dash is also used to attribute a quotation, as in the example above.

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