Here’s a listener:

Hi, Grammar Girl. This is Patti from Houston…

Patti and her friends are debating about the serial comma — the comma that comes before the final conjunction in a list. Here’s a sentence that uses a serial comma: “According to the website Box Office Mojo, the top-grossing movies of all time in the United States are currently ‘Avatar,’ ‘Titanic,’ and ‘The Dark Knight.'”

Whether to use the serial comma is a style issue, which is why Patti and her friends ended up in a debate.

Do you always have to use serial commas?

Although the British are less likely to use serial commas than Americans (1, 2), primarily it’s newspapers that allow writers to omit that final comma (1, 3). Newspapers are always looking to save space, and one argument for leaving the comma out is that it’s unnecessary in simple sentences. Consider this sentence: “When you look at worldwide sales, the top-grossing movies of all time are currently ‘Avatar,’ ‘Titanic’ and ‘Lord of the Rings: The Return of the King.'”

I didn’t use a serial comma in that sentence, and there wasn’t any confusion. That’s the main argument against using the comma in every case — leaving it out often doesn’t change anything.

The serial comma is also sometimes called the Oxford comma because it’s used by Oxford University Press or the Harvard comma because it’s used by Harvard University Press, but I find these names misleading because so many other publications also use the serial comma.

Using serial commas adds consistency

Although the serial comma isn’t always necessary, I favor it because often it does add clarity, and I believe in having a simple, consistent style, instead of trying to decide whether you need something on a case-by-case basis. I also think using the serial comma makes even simple lists easier to read. Really, unless space is incredibly expensive, I can’t imagine why anyone would decide the best method is sometimes leave it out and sometimes add it in.*

Always use serial commas to prevent confusion

The one thing everyone does seem to agree about is that you have to use the comma when leaving it out would create confusion, as is often the case when the items in the list could have internal conjunctions or are complex in some other way (1, 3, 4, 5, 6, 7, 8). Here’s a sentence that could mean different things with and without the final comma: “Rebecca was proud of her new muffin recipes: blueberry, peanut butter and chocolate chip and coconut.”

Without a serial comma, you can’t be sure whether the last recipe is a combination of peanut butter and chocolate chip or a combination of chocolate chip and coconut. You can make the meaning clear in two ways: place the final comma after peanut butter or after chocolate chip, or rewrite the sentence so that there is no ambiguity.

If you want to say that the combination is peanut butter and chocolate chip, you can write “blueberry, peanut butter and chocolate chip, and coconut,” or if you insist on leaving out the serial comma, you can rewrite the list as “peanut butter and chocolate chip, coconut and blueberry.” But I still think the rewrite is more risky than the sentence with the serial comma because a reader who’s just skimming the sentence could be tempted to think that coconut and blueberry is a combination.

Another case where leaving the comma out can be confusing is when the later items in the list can describe an earlier item. An oft-cited example is the made-up book dedication “To my parents, Ayn Rand and God.” A reasonable reader would assume there are four entities being thanked: mom, dad, Ayn Rand, and God; but without the serial comma you could also conclude that the two parents are Ayn Rand and God. A serial comma clears up any confusion: “To my parents, Ayn Rand, and God.”

The bottom line on serial commas

• Finally, there are similar sentences where even a serial comma doesn’t make the meaning clear. Consider this sentence: “I went to see Zack, an officer and a gentleman.”
• Without the serial comma — “I went to see Zack, an officer and a gentleman” — it could mean that Zack is both an officer and a gentleman, or that I went to see three people: Zack, an unnamed officer, and an unnamed gentleman.
• With the serial comma — “I went to see Zack, an officer, and a gentleman” — it could still mean two different things. It could mean I went to see three people (Zack, an unnamed officer, and an unnamed gentleman), or it could mean I went to see two people (Zack, who is an officer, and an unnamed gentleman).
• So, the bottom line is that using the serial comma is a style choice. Most publications except newspapers favor using it all the time, as do I, and all publications call for a serial comma when leaving it out could cause confusion. And sometimes sorting out your meaning is just too much for one little comma and the best option is to rewrite your sentence.
• * I am aware that the final preposition could be left off the end of this sentence without changing the meaning. I considered leaving it off, but decided to write it this way because the timing is better when it is read aloud.

References

• 1.Wikipedia contributors. “Serial Comma,” Wikipedia, The Free Encyclopedia, en.wikipedia.org/wiki/Serial_comma (accessed July 10, 2007).
• 2. Quinion, M. “Oxford Comma,” World Wide Words (accessed July 13, 2007).
• 3. Walsh, B. Lapsing Into a Comma. Chicago: Contemporary Books, 2004, p. 81.
• 4. The Chicago Manual of Style. Fourteenth Edition. Chicago: University of Chicago Press, 1993, p. 173, p. 661.
• 5. Shaw, H. Punctuate It Right. New York: Harper Paperbacks, 1993, p. 77.
• 6. Goldstein, N. ed. The Associated Press Stylebook and Libel Manual. Reading: Perseus Books, 1998, p. 270.
• 7. The American Heritage Guide to Contemporary Usage and Style. Boston: Houghton Mifflin, 2005, p. 100.
• 8. “What is the Oxford comma?” Ask Oxford.com
  accessed July 8, 2007).

Further Reading

• Comma Cause Legal Lad, Adam Freedman, discusses legal cases in which commas determined the outcome.