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Punctuation Guide

The following list provides guidance on the most commonly used and misused punctuation marks.

Apostrophe - Comma - Dash - Hyphen - Italics

Apostrophe (')

Add an apostrophe and an s to most singular nouns to form the possessive, and only an apostrophe for plural nouns (except for a few irregular plurals that no not end in s). If the noun ends in s, x, or z add an apostrophe and an s. (Chicago 7.17–7.18)

An apostrophe is never used to form the plural.

It is used to avoid confusion in plural nouns that are lowercased or are abbreviations. (Chicago 7.14)

  • The Rockville Campus’s building (singular noun ending in s)
  • the Williamses’ new house, but the Joneses (forming a plural, no apostrophe needed)
  • FDR’s legacy
  • 2010’s heaviest snowstorm
  • MA’s and PhD’s
  • the three Rs, the 1900s, threes and fours  (forming a plural, no apostrophe needed)

Straight versus slanted apostrophes

For printed material, the typographer’s mark (“smart quotes”) is preferable to the straight one, which is more prevalent in Internet material and other software applications. MS Word automatically generates the preferred quotation mark.

Comma (,) 

Comma in Dates: In text, insert commas after the date and the year.

  • He was born on July 11, 1955, in Eugene, Oregon. (Chicago 6.45)
  • The event will be held on July 11. (not 11th or 11th)


Comma in City and State Names: Enclose states, provinces, and territories in commas to set it from the rest of the sentence. (Chicago 6.17)

The committee will meet at the Rockville, Maryland, location.


Comma in Proper Names: “Jr.” is no longer set off by commas; neither is a numeral suffix.

Alan Miller Jr. works at the College; but Henry James II does not. (Chicago 6.47)


Comma in Numbers: Insert a comma in numbers of more than three digits.

1,000; $2,580 


Comma in a Series: In lists of three or more items, use a comma before the word “and” and “or.”

They will serve breakfast, lunch, and dinner. (Chicago 6.18)


Dash (and Hyphen)

In typesetting, three distinct symbols are used: hyphen (-), dash (–) also called an en dash, and em dash(—).  

Hyphen:  Use a hyphen in phone numbers and all fractions.

  • 240-567-7000
  • one-third, three-fifths


En dash:  Use an en dash  to indicate a range. The en dash is half the size of an em dash. To insert an en dash into a Word document, click on "Insert" then "Symbols," then "More Symbols," then select the "en dash" from the "Special Characters" tab. The shortcut is Ctrl+Num-

  • 1992–1993
  • pages 12–105
  • 10 a.m.–5:30 p.m.
  • Monday–Friday


Em dash: Use an em dash (made up of two hyphens) or parentheses to set off a full phrase when the phrase contains a series of words that must be separated by commas. Also, use an em dash to denote an abrupt change in thought in a sentence or an emphatic pause.

We will fly to San Diego in June—if the travel expense is approved. 



For titles of movies, television, radio programs, plays, works of art (paintings, drawings, statues), books, and periodicals, use italics. For more guidance on title formatting, see Quotes, Italics, or Nothing? section of this guide.

  • One Flew Over the Cuckoo’s Nest (movie)
  • The Sopranos (TV)
  •  WAMU’s Drive Time (radio show)
  •  Sweeney Todd (play)
  •  Rodin’s Thinker and Grant Wood’s American Gothic (artwork)
  • A Farewell to Arms (book)
  • The Washington Post, Newsweek (periodicals)


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