Punctuation

Commas

Use the comma ( , ):

To separate items in a series.

  • (series of words) – Sophomores, Juniors, and Seniors attended the assembly.
  • (series of phrases) – She got paint on her shirt, on her shoes, and in her hair.
  • (series of clauses) – They came to the party, they drank all the beer, and they refused to leave.

Note: Some writing guides suggest leaving out the last comma in a series: Sophomores, Juniors and Seniors attended the assembly.

To set off all types of nonrestrictive elements (information not necessary to the meaning of the core sentence).

  • New Orleans, home of the po-boy sandwich, is a fascinating city.
  • The marsh, once full of wildlife, is now covered in oil.
  • John, who knows everything about physics, can’t boil an egg.

Note: Do not put commas around essential (restrictive) information: The woman who is sitting four seats to the left is falling asleep. [The location of the woman is essential information].

To set off introductory elements.

  • After leaving high school, he volunteered for two years.
  • Hearing her name called, she rose from her seat in the jury room.
  • In this box, you will find the treasure you seek.

Before a coordinating conjunction (for, and, nor, but, or, yet, so) when used to connect main clauses.

  • We leave food out at night for the stray cats, and it is always gone by the morning.
  • He ran a strong race, but he came in second.

Note: Do not use a comma if the coordinating conjunction connects a main clause and a dependant clause: He ran a strong race but came in second.

To connect free modifiers to a base sentence.

  • The children sat in three straight rows, fidgeting and squirming in their seats.
  • A few hours later we spotted two small dolphins, startlingly beautiful fish of pure gold, pulsing and fading and changing color.

Colons

Use the colon ( : ) after a complete sentence that introduces a list or a full-sentence quotation.

  • There are three major ways to cut your risk of heart disease: exercise regularly, eat a healthy diet, and reduce stress levels in your everyday life.
  • Hemingway expresses the struggles of the writer this way: “There is nothing to writing. All you do is sit down at a typewriter and bleed.”

Semicolons

Use the semicolon ( ; ):

To connect closely related main clauses.

  • We prepared food for fifty guests; only ten diners showed up.
  • He ran a strong race; however, he came in second.

To separate a series of items that contains commas.

  • The committee received suggestions from a veterinarian in Anchorage, Alaska; a lawyer in Medford, Massachusetts, who has handled animal cruelty cases; and an animal rescue worker in New Orleans, Louisiana, who is a specialist in rescuing wild animals in urban settings.

Dashes

Use the dash (—):

To mark any sudden break and add emphasis.

  • She will finally receive her degree in May—if she survives her final exams.

To set off elements added at the end of the sentence.

  • He packed the necessary items in the duffel bag—duct tape, a rope, and an axe.

To set off interrupters, especially when they contain commas (a dash works as a “strong” comma).

  • The necessary items—duct tape, a rope, and an axe—were packed in the duffel bag.

Notes: A dash is not a comma substitute. Use it only sparingly, such as in the cases described above.

Parentheses

Use parentheses ( ) to set off and de-emphasize explanatory or less important details inserted into a sentence:

  • Oswaldo was born in Honduras (although he lived there only seven years).

Apostrophes

Use the apostrophe ( ’ ):

To mark a possessive.

  • That is Ann’s yogurt, so please do not eat it. [singular word, not ending in “s”]
  • The cats’ tails were twitching in irritation. [plural word]
  • The children’s snacks filled the ice chest. [word that is plural without adding “s”]

Note: The possessive form of “its” doesn’t use an apostrophe: That coat is losing its buttons.

To mark the missing part of the word in a contraction (and other omissions).

  • That’s Ann’s yogurt, so please don’t eat it.
  • It's ten o'clock. [originally "It is ten of the clock."]

To form certain plurals when clarity is an issue.

  • The old typewriter doesn’t type e's. (“The ole typewriter doesn’t type es” has a different meaning).