The serial comma (a.k.a. the Oxford comma or the Harvard comma) is the comma used immediately before the conjunction that precedes the final item in a series of three or more items. In simple sentences, omitting the serial comma may be acceptable; however, ambiguities causing misinterpretations arise in more complex sentence constructions.
Its use is mandatory in U.S. English; in the U.K. and Canada it is optional. Newspapers and magazines tend to omit simply to save space. In the Canadian public education system, it appears that educators actually teach students that it’s wrong to use a serial comma. *Sigh* — some teachers are very misinformed.
However, even grammar authorities disagree on this issue. Style guides in support of the serial comma’s use include: The Chicago Manual of Style, The American Medical Association Manual of Style, and Wilson Follett’s Modern American Usage: A Guide. Style guides that support omitting the serial comma include: The Times, The Economist, and the AP Stylebook.
In business and technical writing, the standard practice is to include the serial comma. The Gregg Reference Manual, the standard for business and technical writing in Canada, recommends the inclusion of the serial comma.
If you’re a writer working on your novel or manual, use the serial comma. If your job is to write for a company or organization, you should let their style guide decide for you. In my writing, I prefer consistency, so I always use it.
Why You Should Use the Serial Comma
Examples without the final comma:
1) I made sandwiches for the picnic consisting of ham, egg salad and peanut butter and jam.
Without the serial comma, this sentence is as clear as mud. Are there three or four types of sandwiches?
Better: I made sandwiches for the picnic consisting of ham, egg salad, and peanut butter and jam.
Commas omitted can also cause problems in legal documents. For example:
2) Mrs. Jane Doe leaves all her money to her three children: Tom, Dick and Harry.
Legal interpretation of this sentence would mean that “Tom” gets one-half of the money and “Dick and Harry” will split the other half. If their mother intended the money to be equally split, then the serial comma is required.
And finally consider the interpretation of this sentence as it stands without the serial comma:
3) Jennifer thanked her parents, Mother Theresa and God.
Without that final comma, it’s implying that Jennifer is the divine offspring of … well, you get the picture.