The Oxford Comma: What It Is and When to Use It
What is the Oxford comma, when should you use it, and is it ever truly necessary? We explain the serial comma with clear examples and a few amusing pitfalls.
The Oxford comma — also known as the serial comma or Harvard comma — is the final comma in a list of three or more items. It takes its name from the house style of Oxford University Press, the historic UK publisher.
As an example, consider these two lists:
Example 1: Norway, Germany and China.
Example 2: Norway, Germany, and China.
The two are punctuated differently: the Oxford comma falls right after “Germany” in the second example, while the first omits it entirely.
So, should you use the Oxford comma in your own writing?
Opinions differ. As a broad rule, writers using British English tend to avoid the Oxford comma, while in American English it is relatively common. As ever, exceptions exist on both sides.
One notable exception is New Hart’s Rules (the Oxford style guide), which recommends the Oxford comma wherever its absence would cause confusion or ambiguity. For example:
Example 3: We studied George III, William and Mary and Henry VIII (without the Oxford comma).
Example 4: We studied George III, William and Mary, and Henry VIII (with the Oxford comma).
In Example 3, the missing comma obscures the fact that “William and Mary” is a single list item. Example 4 solves this by placing a comma immediately before the coordinating conjunction (“and”).
When push comes to shove, then, using or avoiding the Oxford comma is largely up to you. Whatever you decide, be consistent, and punctuate deliberately.
If you are writing a scientific paper or a technical document, think carefully about whether omitting or including the Oxford comma could create unwanted ambiguity. In a context where unambiguous language is not essential, you might leave it out for aesthetic reasons.
Most importantly, note the American style guides that mandate the Oxford comma, including The Chicago Manual of Style, the MLA Handbook, and APA Style. And remember that Oxford’s own New Hart’s Rules requires it in certain cases.
On a final — slightly amusing — note, watch out for the strange misunderstandings that dropping the Oxford comma can produce:
Example 5: I had lunch with my father, Barack Obama and the Prime Minister of Switzerland.
Without the Oxford comma, a reader might take Example 5 to mean that you had lunch with your father, and that your father is both Barack Obama and the Prime Minister of Switzerland. To reduce the confusion, we can add the Oxford comma:
Example 6: I had lunch with my father, Barack Obama, and the Prime Minister of Switzerland.
That solves the problem — well, almost. Example 6 now showcases one of the surprising quirks of English: it is no longer clear whether “Barack Obama” is an appositive describing “father” or simply the second item in a three-item list.
For some writers, this appositive problem makes the Oxford comma useless. For others, it is the lesser of two evils, so they use it habitually. Both are perfectly reasonable positions.
Now that you have the Oxford comma covered, you might find it useful to learn more about appositive phrases — see our companion article on appositives.