Dashes can be used like commas or parentheses to set off parenthetic material, or like colons to introduce clauses, which clarify or expand on the preceding material. Personal preference often decides the choice of mark to use.

The dash is used to:

1. Mark a sudden break or change of direction in a sentence.
   
   
   • The evening clientele appeared to be satisfied with the new menu, but the luncheon crowd-that was quite different.
   • The speaker then went on to declare that-
   
   
2. Indicate an interruption in speech, hesitation, or confusion.
   
   
   • "Yes," he continued, "I mean that-I saw her two nights ago-I guess-I think it was two nights ago."
   
   
3. Emphasize parenthetical or explanatory material in place of commas or parentheses
   
   
   • He claimed-and no one stood up to contradict him-"A blond woman was the last person to leave the office."
   • The fuel was a mixture of many different organic compounds-all based on carbon atoms-obtained from the local petroleum refinery.
   
   
4. Set off or introduce defining phrases.
   
   
   • If the tax cut is rescinded-God be willing-the terrible deficit will be reduced considerably.
   • The young Spaniards from Barcelona typically spoke at least three languages-Spanish, Catalan, English or French-and often four.
   
   
5. A dash is often used in place of a colon or semicolon to link two clauses, especially if the second clause clarifies or summarizes the first clause in dramatic fashion.
   
   
   • The race was finally over-it had been an exhausting ordeal.
   
   
6. To set off explanatory or illustrative material by phrases, such as for example, namely, and that is, if a dash helps to convey the meaning better than would the use of a comma.
   
   
   • Conventional media-such as radio, television, and newspapers-were considered impractical because of their high advertising rates.
   
   
7. To introduce a statement that summarizes a preceding series of words, ideas, or phrases.
   
   
   • An attractive design, good handling and turning characteristics, a low center of gravity, quick acceleration, fuel economy, lots of interior space, and an excellent radio and CD player with four speakers-the new model offered something to all members of the family.
   
   
8. To precede a credit line, signature, or name of an author or source at the end of a quotation or quoted passage.
   • "The more I see of men, the more I like dogs." -MADAME DE STAËL.

The en dash is shorter than an em dash, although longer than a hyphen. It is a special character in word processing programs. Newspapers use a hyphen in its place. The en dash is commonly used:

1. In combinations of numbers, upper case letters, or numbers and uppercase letters.
   • exhibit 6-D
   • I-89 (interstate)
   • $12-$15
   • NBC-TV
   • 4-H Club
   • 305-999-1212 (telephone number)
   
   
2. To denote a period of time without using "to".
   
   
   • 1907-86
   • November-March
   • Tuesday-Thursday