Comma Usage in a Series

A Style Guide of When to Use or Omit the Serial Comma in a List

Aug 21, 2008
Megan B. Wyatt

Many people argue for the serial comma. - MBIMOTMOG

All the ands, buts, and ors about using commas in a list. Learning the basic rules will aid your writing whether you're shooting an email or writing a business document.

Everybody learns comma usage rules in school, but what are the chances of remembering every subrule and exception? Not so high for the everyday non-English major.

Although the tip of placing commas where a person would pause in normal speech can be useful, this trick does not guarantee proper comma placement. It can often lead to misplaced, overused, or missing commas, especially when writing a series of words or phrases.

The Serial Comma

Anytime you write a list of items, phrases, directions, or just about anything, you should separate each item, phrase, direction, etc. with a comma. But, there's the controversial final comma sometimes included or omitted before the conjunction (and, or, but) of a sentence, depending on the situation and style. This final comma is most commonly known as the serial comma, but it may also be called the Oxford or Harvard comma.

The Basic Rule for Commas in a Series

In most cases, use or omission of the serial comma is equally correct, but in certain circumstances the comma should be included or omitted based on clarity, style, or preference. The following sentences are generally considered correct, especially in casual, email, or internet writing.

Patty ate a sandwich, a bag of chips, and an orange for lunch.

Patty ate a sandwich, a bag of chips and an orange for lunch.

Commas in a Simple List of Items

Different writing styles and countries have different preferences and rules on the final comma in a simple list of items.

MLA Style - The Modern Language Association's guidelines are followed throughout North America, Brazil, China, India, Japan, Taiwan, and other countries, and MLA Style includes the use of the serial comma before the conjunction.
APA Style - The American Psychological Association's guidelines use the serial comma as well.
AP Style - The Associated Press guidelines omit the serial comma, except in the case of lengthy phrases or to reduce ambiguity.
American Style - Generally, American style is to use the serial comma.
British Style - Generally, British style is to omit the serial comma.

Use of the Serial Comma to Reduce Ambiguity

Usually the serial comma reduces ambiguity, but sometimes it introduces it.

In the following examples, omission of the serial comma does not affect the sentence's overall meaning.

Tina has dated Greg, Justin, Cameron and Zach.

Tina has dated two plumbers, one engineer and one businessman.

But in the following cases, omitting the serial comma could cause confusion.

My favorite chips are mesquite barbeque, cool ranch, sour cream and onion and garden salsa.

George left for Florida with his parents, Greg and Dianne.

In the first sentence, it is unclear if one of the favored chips is sour cream and onion or onion and garden salsa. Adding the serial comma after onion would reduce ambiguity.

In the second sentence, it is unclear whether George's parents are named Greg and Dianne, or if Greg and Dianne are two people who went with George and his parents. If Greg and Dianne are not his parents, the serial comma should be added after Greg to reduce ambiguity.

Omitting the Serial Comma to Reduce Ambiguity

Though the serial comma usually reduces ambiguity, in the following examples, including the serial comma might introduce ambiguity.

Ross, a poet, and a giraffe crossed the African desert.

Jonas dedicated the film to his first grade teacher, Jennifer Davis, and his mom.

In the first example, the sentence could read that Ross is a poet who is traveling with a giraffe or it could read that Ross traveled with a poet and a giraffe. Removing the serial comma would clarify that Ross traveled with a poet and a giraffe.

In the second sentence, it is unclear whether Jonas dedicated the film to his teacher named Jennifer Davis or two separate people. Removing the comma would clarify his dedication to three people.

Use or omit the serial comma based on the style of writing required or preferred. Use common judgment when a sentence could be misinterpreted, although these cases are rare. Always use the serial comma in lengthy phrases or clauses. In general, your point will be received whether you choose to include the serial comma or not.