The dash tends to be a slightly enigmatic punctuation mark.  Grammar books and guides (such as the ones consulted for this handout) usually present the same general concepts regarding dashes but with different explanations or reasoning.  It is acceptable to use a dash in the following instances:

  • To separate an introductory phrase from the main sentence
  • To set off an appositive containing a comma
  • To indicate an interruption in a quotation
  • To interject an alternative opinion
  • To emphasize a particular part of a sentence

Separating an introductory phrase from the main sentence

Separating an introductory phrase from the body of the sentence can often be done effectively using just a comma.  When a comma is present in the introductory phrase, however, some writers prefer to separate the two sections with a dash.  One hint is to watch for the words like “these,” “those,” or “all” as the first word in the main part of the sentence.

Ex: A reliable coffeemaker, a bright reading lamp, and a slightly uncomfortable chair – these are the ingredients for a successful all-nighter.

Setting off an appositive containing a comma

An appositive is a word or phrase that restates or redefines a nearby noun.  In general, appositives are set off by commas, but when they contain a comma, a dash is used to improve the clarity of the sentence.

Ex: The fruit they’d brought back from Spring Break—a mix of bananas, papayas, and mangoes—was confiscated by the airport authorities.

In this example, “the fruit” and “a mix of bananas, papayas, and mangoes” refer to the same thing.  The former is the noun and the latter is the appositive.  Because the appositive contains commas, it is correctly distinguished from the rest of the sentence by dashes.

Indicating an interruption in a quotation

When writers want to indicate that a quotation has been interrupted, they use a dash.

Ex:  John exclaimed, “I have more homework than any—“  “Don’t start with me,” his mother interrupted, “I did twice the work you do when I was in college!”

Indicating an alternative opinion

The dash can be used to insert an additional opinion or perspective into a single sentence.

Ex: In my opinion—but not my parents’—going to school in another state was a splendid idea.

Emphasizing or dramatizing a particular part of a sentence

Writers also choose to punctuate a sentence with a dash when they want to accentuate one component of a sentence.  It is in these cases that the drama of the dash is very useful.  In order for the dash to maintain its emphasis, it’s important to not overuse the dash for the punctuation above in any individual paper.

Ex: After the snow melted, the Messalonskee stream was rushing through the riverbed—and the streets.

The student employees would work hard—but not too hard.

**Hint: When typing the dash, type two hyphens (–) without spaces on either side.  Word processing programs should automatically turn the two hyphens into one long dash (—).