"Dashes and Parentheses" was written by Joe Moxley.
Some stylists view the dash with great suspicion--the sort of suspicion that a man in the 1990s who wears a plaid leisure suit to work would arouse. Some people erroneously believe that the dash is acceptable only in informal discourse. However, the dash can provide you with subtle ways to repeat modifiers and dramatic ways to emphasize your point.
Use a Dash after a Series or List of Appositives
When you introduce a long series or list of appositives before the subject and verb, you are placing high demands on the reader's short-term memory. Therefore, use this pattern rarely and only for emphasis. This pattern is particularly appropriate in conclusions, when you are bringing together the major threads of your discussion or argument. Finally, you should place a summary word after the dash and preferably before the subject of the sentence, as indicated by the following examples. The most common summary words that writers use are all, those, this, each, what, none, such, these.
Use Dashes When You Wish to Emphasize a Parenthetical Element
Commas are usually sufficient punctuation to set off parenthetical elements. In some instances, however, you can use a dash instead, especially if you want to make the insertion more noticeable:
When you want to whisper rather than shout, you can place the modifiers inside parentheses:
Use Dashes to Embed a Series or List of Appositives
A single appositive or modifier can easily be set off from the rest of the sentence in commas, but you must use dashes when you insert a series of appositives or modifiers. After all, how else will the reader know when the series is over?
Use Dashes to Set off an Emphatic Repetition
You can emphasize an important point by placing a dash or comma at the end of the sentence and then repeating a key word or phrase:
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