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.
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.”
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.
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.
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).
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).