What Is the Oxford Comma?
The Oxford comma, also called the serial comma, is the comma placed before "and" or "or" in a list of three or more items. In the sentence "I bought apples, oranges, and bananas," the comma after "oranges" is the Oxford comma.
Some style guides require it (Chicago Manual of Style, APA). Others omit it as a default (AP Stylebook, most UK journalism). The debate has raged for decades, and it is not merely academic.
Why It Matters
Consider this sentence without the Oxford comma: "I admire my parents, the president and a talk show host." Does the writer admire three separate entities, or is the writer saying their parents are the president and a talk show host? The ambiguity is real, and in some cases, it has legal consequences.
In 2017, a Maine labor dispute hinged on a missing Oxford comma in state legislation. The ambiguous sentence cost a dairy company millions in overtime payments. The case, O'Connor v. Oakhurst Dairy, became a landmark example of how punctuation affects meaning.
When to Use It
Always use it when omitting it creates ambiguity. This is the non-negotiable rule, regardless of which style guide you follow. If removing the comma could cause a reader to misparse the sentence, keep the comma.
Use it by default if your style guide allows it. Consistency matters more than the individual choice. If you use the Oxford comma sometimes and skip it other times, your writing will feel inconsistent.
Skip it only when the meaning is clear without it. "I ate eggs, toast and juice" is perfectly clear. No one will read "toast and juice" as a compound item. In cases like this, omitting the comma is a legitimate stylistic choice.
The Practical Advice
If you are writing for yourself, pick a side and be consistent. If you are writing for a publication, follow their style guide. If you are writing anything where clarity is paramount, contracts, instructions, technical documentation, use the Oxford comma every time. The tiny cost in ink is worth the clarity it buys.
The Oxford comma will not make you a better writer. But it will prevent you from accidentally telling the world that your parents are a president and a talk show host.