Grammar Girl here.

Today's topic is the serial comma.

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 Internet Movie Database, the top-grossing movies of all time in the United States are currently Titanic, Star Wars, and Shrek 2.

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

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: According to the website Box Office Mojo, when ticket sales are adjusted for inflation, the top-grossing movies of all time in the United States are currently Gone with the Wind, Star Wars and The Sound of Music.

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. (And I apologize to the international listeners for using U.S. ticket sales in the example. I couldn't find inflation-adjusted numbers for worldwide box office sales.)
 
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.

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*.

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 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 because one of the list items has an internal conjunction: Rebecca was proud of her new muffin recipes: blueberry, peanut butter and chocolate chip and coconut.

Without a serial comma, you wouldn't know 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. 

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 whether or not to use the serial comma is a style issue. 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.

That's all.

I have an exciting announcement this week! My audiobook is coming out soon on a physical CD that you can buy in bookstores. Of course it will still be available to download from iTunes and Audible.com, but I know some people would rather have something they can hold in their hand or wrap up and give as a gift. It'll be available in all the major bookstores on July 24th, and you can already pre-order it online. I'll put a link at my website. QuickAndDirtyTips.com, and while you're there, be sure to also check out the other great Quick and Dirty Tips podcasts such as Money Girl. This week she's talking about how to avoid problems when you marry someone who has poor credit.

Also, for those of you who've asked, I am working on a paperback book, but those things take a really long time, so it probably won't be available until next year about this time.

Thanks for listening. My e-mail address is feedback@qdnow.com and if you want to leave a question for me to use in the show as Patti did, the number is 206-338-GIRL, 206-338-4475.

* 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, www.worldwidewords.org/qa/qa-oxf1.htm (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. www.askoxford.com/asktheexperts/faq/aboutother/oxfordcomma?view=uk (accessed July 8, 2007).