Appendix A: Punctuation
apostrophe (') Use an apostrophe with plurals of single letters and for shortening decades except when the figure follows "mid-": A's, B's and C's; the '70s, mid-70s.
Don't use an apostrophe with plurals of figures or words or multiple letters: in the 1800s; 10s and 20s; ifs, ands or buts; ABCs, IOUs.
Also see possessives.
colon ( : ) The most frequent use of the colon is at the end of a sentence to introduce lists. When the introduction is not a complete sentence and one or more of the items on the list are needed to complete, no colon is used.
Capitalize the first word after a colon if it's a proper noun, if it starts a complete sentence, or if it's the first word in the second part of a composition title: "Corporate Raiding: An Insider's View."
comma ( , ) Use a comma to:
Set off state from the rest of the sentence when used with city: He moved to Bethesda , Md. , after living in Montana five years.
Set off a date preceded by a day of the week: The event will be on Monday, Nov. 5, at UM.
Set off quotations: The sergeant said, "I can't hear you." "Honey, I'm home," Ward said.
Separate equal adjectives: a thoughtful, precise manner; the free, public lecture. Equal adjectives can be reversed or scrambled.
Separate two independent clauses — groups of words that could stand on their own as sentences — joined by a conjunction such as "and," "but," "or": I went to the store, and I spent far more than I'd planned. Come in, but shut the door behind you.
Set off nonessential clauses and phrases. See essential, nonessential clause/phrase entries.
Avoid comma splices — joining two independent clauses with a comma but no conjunction. Wrong: I liked my history class, my professor was the best I've ever had. Use a period, semicolon or comma and conjunction instead: I liked my history class. My professor was the best I've ever had. Or: I liked my history class; my professor was the best I’ve ever had.
Omit the comma between the last two items in a series unless needed for clarity: Jake, Melanie and Sierra came to my party.
Use a comma with numbers: 1,000 men, $66,000, 12,000 acres.
Look out for these tricky cases:
My husband, Ralph, drives a bus. You have only one husband, so you set off "Ralph" with commas. See essential, nonessential phrase entry.
My son Robert is a pyromaniac. You have three sons, so you don't set off "Robert" with commas. See essential, nonessential phrase entry.
I went to the store, where I bought $50 worth of bananas. Notice how the meaning of this sentence changes when you omit the comma: I went to the store where I bought $50 worth of bananas. See essential, non-essential clause entry.
dash ( — ) Most commonly used to indicate an abrupt change in thought or to set off a series of words that would otherwise be separated by commas: I'll get to New York City — I don't care how — or die trying. He had the qualifications — hands, height, speed and agility — of a promising basketball star. Leave a space on each side of the dash. Two hyphens may be used for a dash, if necessary.
ellipsis ( ... ) Use an ellipsis to show you've deleted one or more words in shortening quotes, texts and documents. In general, treat an ellipsis as a three-letter word; use three periods with one space on each side of ellipsis.
When the words before an ellipsis form a complete sentence in the original or condensed form, use a period at the end of the last word before the ellipsis. I didn't want to teach anymore. ... Will you be there? ...
When you delete material at the end of one paragraph and the beginning of the next one, put an ellipsis in both places.
Don't use ellipses at the beginning and end of direct quotes: "I've had enough," the vice president said. Not "... I've had enough, ..." the vice president said.
To show hesitation: What ... what makes you say that?
exclamation point ( ! ) Avoid. It is seen as amateurish. See quotation marks entry.
hyphen ( - ) Use a hyphen to:
Join compound modifiers: second-quarter report, half-time job, record-breaking sprint. Don't hyphenate two-word modifiers that include the adverb "very" and adverbs ending in "-ly": very good grades, beautifully illustrated book.
Avoid ambiguity: He re-covered his roof. She spoke to small-business women.
Indicate suspensive hyphenation: She received a 15- to 20-year sentence in the state prison.
Note: Many compounds that are hyphenated before a noun aren't hyphenated when they follow a noun: I have a half-time job. I work half time.
parentheses ( ) In general, avoid. They disrupt the flow of a sentence, distracting the reader. The information usually can be deleted or left where it is without parentheses.
quotation marks (" ") Commas and periods go inside quotes. Colons and semicolons go outside.
Exclamation points and question marks go inside the end quotation marks if they apply directly to the quoted material; otherwise, they go outside the quotes: She asked, "Do I have to take the test?" Did she say, "I'm leaving now"?
If a full paragraph of quoted material is followed by a paragraph continuing the quotation, don't put close-quote marks at the end of the first paragraph. Do put open-quote marks at the start of the second paragraph.
If a paragraph doesn't start with quotation marks but ends with a quotation that's continued in the next paragraph, don't use close-quote marks at the end of the first paragraph if the quoted material forms a complete sentence. Do use close-quote marks if the quoted material doesn't form a complete sentence.
semicolon ( ; ) Connects two closely related ideas: The conference drew participants from across the country; two came from as far away as Nome, Alaska.
Use semicolons in a series when at least one of the items in the series includes punctuation: My children are David, 5; John, 3; and Suzanne, 1. For clarity, you may also use semicolons to separate items in a lengthy series in which no individual item includes internal punctuation.