Dashes and hyphens are different punctuation marks and are not interchangeable.

Em-Dashes
An em-dash or double hyphen is frequently over-applied by insecure writers. Rather like the colon, which appears in nearly every undergraduate term paper title, its use is aggravated by a false hope that more dashes will equal less confusion.

The em-dash can be an effective alternate to the use of a colon or comma, depending on the grammatical circumstances. The em-dash which replaces a colon interrupts a sentence. The use of two em-dashes within a sentence indicates interruption to the middle of a sentence by information which relates to the material immediately before the first em-dash; it would not replace parentheses, which contain information not as fundamentally bound to the sentence.

The Thomson Handbook suggests em-dash usage: "to set off material that interrupts the flow of a sentence, to emphasize appositives and examples, to set off a term's definition, to set off an aside (a personal comment), to mark a shift in tone, to indicate a hesitation or a break in dialogue, and to emphasize statements that summarize or describe a list of items" (960). The Thomson Handbook also suggests, "dashes should be used sparingly --normally you should limit yourself to one set in a paragraph" (960). Commas can be used elsewhere for the same functions, although they indicate less emphasis. A paragraph with too many dashes may appear choppy and give the impression of sensationalism.

Patricia O'Conner provides the following advice: "If a sentence has a smaller sentence within it (surrounded by dashes or parentheses), don't use a period to end the "inside" sentence: When Apu made him an offer--"I could use some help around the store"--he accepted." (135) She also suggests that, "Dashes thrive in weak writing, because when thoughts are confused, it's easier to stick in a lot of dashes than to organize a smoother sentence. Whenever you are tempted to use dashes, remember this:

• Use no more than two per sentence. And if you do use two, they should act like parentheses to isolate a remark from the rest of the sentence: After the flight, Tina looked--and she'd be the first to admit it--like an unmade bed.
• If the gentler and less intrusive parentheses would work as well, use them instead. Tina's luggage (complete with her return ticket) appeared to be lost." (144-145)

The following is an example of the incorrect usage of the em-dash:

• With infinite slowness he raised his hand--he lifted an arm and tore off the bandage--he stood up. When I grow up I'm going to become president--climb Mt. Everest, and travel to Mars.

En-Dashes
According to Sparknotes.com, "En dashes are used to indicate a stretch of time between dates." En-dashes can be placed between two dates instead of "to" or "and". An en-dash should never be coupled with the word "from", instead use the word "to" in between the two dates. See the examples below:

• We crossed the New Mexico-Arizona border on foot.

The hyphen is misapplied by users of word processors who avoid taking extra time to find a synonym or a less awkward way to connect two words. It is not a reliable indicator that the two words should connect. Note that "treeeyed" returns a red underline, but that "tree-eyed" does not. Does tree-eyed make any sense? Probably not, unless it's a (dubious) poetic conceit.

Hyphens have two purposes. The first purpose is to connect two or more words, such as in terms for some family members (mother-in-law), two-word descriptions (quasi-official) or fractions (two-thirds). The second purpose is to connect parts of words that have been separated at the end of a line due to space issues. According to Patricia O'Conner, the author of Woe Is I, "One of the hardest things to figure out with hyphens is how to use them in two-word descriptions." (145-146) O'Conner provides two simple guidelines on when to use hyphens. "If it's after the noun, don't use a hyphen [ . . .] If it's before the noun, use a hyphen when either of the two words in the description wouldn't make very much sense by itself." (145-146) See the examples below:

• Father is strong willed.
  
• My cousin is red haired.
  
• This chicken is well done.
  
• Ducks are water resistant.
• He's a strong-willed father.
  
• I have a red-haired cousin.
  
• This is well-done chicken.
  
• Those are water-resistant ducks.

Martha Kolln uses the examples of 'English-speaking world' and 'four-door minivan'. Here she shows "the hyphen makes clear that English modifies speaking world and that four modifies door, not minivan (176). This is the correct use of the hyphen to relate two words. She goes on to say "Another occasion for hyphens in preheadword position occurs when we use a complete phrase in the adjective slot: 'an off-the-wall idea,' 'the end-of-the-term party'" (177).

Patricia O'Conner provides the following examples in her book Woe Is I. (145-146) These examples are cases where a hyphen must always be used:

• With ex (meaning "former"). Hal is the ex-president of the company.
• When adding a beginning or an ending to a word that starts with a capital (anti-British, Trollope-like). Two exceptions are Christlike and Antichrist.
• When adding like would create a double or triple l (shell-like).
• When adding a beginning or ending would create a double vowel (ultra-average, anti-isolationist). But pre and re are often exceptions to this (preempt, reexamine), so when you have a duplicate vowel, look up the word in the dictionary. (The vowels are a,e,i,o,u.)
• With fractions. Three-quarters of the brownies and two-thirds of the cookies are gone.

Geraldine Woods, the author of English Grammar for Dummies, offers "another simple rule concerning hyphens, but one that may be on the way out [. . .] If two words are being used as a single description, put a hyphen between them if the description comes before the word that it's describing." (332-334)





Blakesley, David and Hoogeveen, Jeffrey L. The Thomson Handbook. Boston: Thomson Wadsworth, 2007.

Dashes. SPARKNOTES. 10-28-08 <http://www.sparknotes.com/writing/style/topic_55.html>.

Kolln, Martha. Rhetorical Grammar: Grammatical Choices, Rhetorical Effects. 5th ed. New York: Pearson, 2007.

O'Conner, Patricia T. Woe is I The Grammarphobe's Guide to Better English in Plain English. New York: The Berkley Publishing Group, 2003.

Woods, Geraldine. English Grammar for Dummies. Hoboken, 2001.