Punctuation marks are a written convention that make reading and writing more understandable for readers and writers by ensuring the clarity of written language. There are four rules for using dashes as punctuation marks in written American English:
- Separate appositives with commas
- Introduce explanations
- Introduce emphasizations
- Introduce explanations of series
The following sections explain and provide examples of the punctuation rules for dashes in written English. Note that a dash may be written as a dash (—) or three hyphens (—).
Separate Appositives with Commas
Use a set of dashes to separate an appositive that contains commas or both commas and semicolons from the rest of the sentence. For example:
- My favorite characters—Harry Potter, Lyra Belacqua, Frodo Baggins, and Jacob Black—all moved easily from their books to the big screen.
- We plan to visit three big cities—St. Louis, Missouri; New Orleans, Louisiana; and Las Vegas, Nevada—next year.
Do not use dashes to separate appositives that do not contain commas or commas and semicolons.
Use a set of dashes to enclose an explanation that is not part of the grammatical structure of the sentence. For example:
- The Sixth Amendment—the right to a speedy and public trial—ensures that an accused criminal will not sit in prison for an unreasonable amount of time before their trial.
- The third law of motion—the law of reciprocal actions—explains why that contraption with five metal balls found in many medical offices keeps bouncing back and forth.
Do not use dashes to enclose an explanation that is part of the grammatical structure of the sentence.
Use a dash or a set of dashes to introduce an emphasization with a high level of emphasis. For example:
- The brother—the one who is always in trouble—was arrested again last night.
- The idea that boys are smarter than girls is ridiculous—even preposterous.
- Do not use dashes to introduce an emphasization with a moderate level of emphasis.
Enclose Explanations of Series
Use a set of dashes to enclose an explanation of a series that precedes the sentence. For example:
- Love, patience, kindness, understanding—these are traits that a good parent must possess.
- Nouns, adjectives, determiners, verbs, adverbs, prepositions, conjunctions, and interjections—the eight parts of speech in the English language must be studied for a thorough understanding of English grammar.
Em Dash (—) versus En Dash (–)
Although the em dash (— or —) used without spaces is the traditional format of the dash in written English, some style manuals also allow or require the en dash (– or –) with a space on both sides in place of the em dash. Note that the en dash is often preferred in e-language and other electronic uses of language for spacing reasons.
Punctuation is a written convention that helps readers and writers more clearly understand writing by ensuring the clarity of written language. Dashes perform four basic functions in written American English: separate appositives with commas, introduce explanations, introduce emphasizations, and introduce explanations of series.
For information on the use of parentheses—a punctuation mark that is closely related to the dash—in written American English, please read the article Punctuation Rules for Parentheses in Written English.
Faigley, Lester. 2003. The Brief Penguin Handbook. New York: Pearson Longman.
Gibaldi, Joseph. 2003. MLA Handbook for Writers of Research Papers. 6th ed. New York: The Modern Language Association of America.