Serial comma

The serial comma is a comma used before the word "and" or "or" in a list of three or more items.

General

The phrase "ham, chips, and eggs" is written with a serial comma, but "ham, chips and eggs" is not. It is also known as the Oxford comma or Harvard comma.

Most authorities on modern American English usage recommend using the serial comma. The AP Stylebook is the most prominent exception. Certain newspapers, such as the New York Times, omit the serial comma (supposedly to save space). In British and Australian English, the serial comma is normally not used except when its absence produces ambiguity. The alternate names for the serial comma come from Oxford University Press and Harvard University Press, who do use it in their publications.

The main justification cited for the serial comma is to reduce ambiguity. However, whichever convention is followed the writer may be forced by ambiguity to use the alternative or to rephrase the sentence. Consider the following examples.

Resolving ambiguity

Use of the serial comma can remove ambiguity.

"To my parents, Ayn Rand and God" creates ambiguity about the writer's parentage. A comma before the "and" would clarify.

With the final comma, the list "Buy bread, bacon, macaroni, and cheese" means:

1. bread
2. bacon
3. macaroni
4. cheese

But without the final comma, it can also mean:

1. bread
2. bacon
3. macaroni and cheese

The final comma makes it clear that the desired item is not the integrated product called "macaroni and cheese", but instead plain macaroni.