What Is an Oxford Comma?

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Oxford Comma (The Quick Answer)
An Oxford Comma is a comma used before the last list item in a list of three or more items.

Oxford Comma definition

When there are three or more list items, then those following "US convention" should use a comma (often called an Oxford Comma) with the conjunction (usually "and" or "or").
  • Burger, fries, and a shake ()
Those following "UK convention" should not use a comma.
  • Fish, chips and peas ()
If breaking this convention makes the text clearer, then break convention. Clarity trumps both conventions.

With two items in a list, don't use a comma to separate the list items (unless it helps your reader).
Oxford Comma? Y/N? Do our poll.

Oxford Comma

Should you put a comma before "and"? I really wish that were a yes/no question. Unfortunately, it's not.

The aim of this page is to answer that question for you and to introduce you to the Oxford Comma (also called the "serial comma"). Be aware that some people would happily start a fight with you for not using an Oxford Comma while others find the Oxford Comma a complete waste of printer ink or screen pixels.

A Comma with Two List Items

The whole world agrees that when there are two single-word items in a list, there is no need to use a comma before the "and" (called a coordinating conjunction). For example:
  • Bacon and eggs
However, when the list items are longer (NB: We're still talking about two list items at this stage) and especially when they include the word "and," there is a debate on whether you should use a comma. In other words, which version below should we write?
  • The Bakerloo line runs between Harrow and Wealdstone and Elephant and Castle.
  • The Bakerloo line runs between Harrow and Wealdstone, and Elephant and Castle.
In situations like these, use a comma before the "and" if it eliminates ambiguity or simply helps your reader to spot the list items more easily. Therefore, the second version above is the most appropriate.

Let's look at another example:
  • There are delays between The Embankment and Elephant and Castle.
So, are the delays between "The Embankment and Elephant" and "Castle" or are the delays between "The Embankment" and "Elephant and Castle"? A comma would eliminate that ambiguity. For example:
  • There are delays between The Embankment, and Elephant and Castle.
NB: At this point, we're not talking about the Oxford Comma. We're just talking about a clarity issue. The Oxford Comma is a comma used when there are three or more list items.

The Oxford Comma (Three or More List Items)

When there are three or more list items, things start getting a little more complicated because there is no unified position on whether to use a comma with the "and" before the last list item. For example:
  • Bacon, eggs, and tomatoes. ()
    • (The comma with the "and" in this example is the Oxford Comma. This is the convention followed by most (but not all) Americans.)
  • Bacon, eggs and tomatoes. ()
    • (This is the convention followed by most (but not all) Brits. The most notable exception is the Oxford University Press, after which the Oxford Comma gets its name.)
You should follow whatever convention your company follows. If you don't have a company convention, then copy the convention used in a decent national newspaper. If you're free to make your own mind up, then pick a convention and be consistent. That is the golden rule.

A Summary of the Oxford Comma

In summary:
Followers of the Oxford Comma
(generally Americans)
  • I visited New York and London.
    • (There is no need for a comma with just two list items.)
  • I visited New York, Paris, and London.
  • I visited New York, Paris and London.
Avoiders of the Oxford Comma
(generally Brits)
  • I visited New York and London.
    • (There is no need for a comma with just two list items.)
  • I visited New York, Paris, and London.
  • I visited New York, Paris and London.

Does the Oxford Comma Eliminate Ambiguity?

The Oxford Comma is useful for showing the separations between the list items. For example:
  • I like to have a mug of tea, bacon and eggs and toast.
As there is no Oxford Comma in this list, it is unclear whether the list represents:
  • A mug of tea.
  • Bacon and eggs.
  • Toast.
or
  • A mug of tea.
  • Bacon.
  • Eggs and toast.
However, with an Oxford Comma, there can be no ambiguity:
  • I like to have a mug of tea, bacon and eggs, and toast.
The downside of the Oxford Comma is that it can sometimes introduce ambiguity because commas can be used as parenthetical punctuation, i.e., like parentheses (i.e., round brackets). Look at these two sentences:
  • Jack left the pub with John (a policeman) and Simon.
  • Jack left the pub with John, a policeman, and Simon.
Both of these examples are fine grammatically. However, if you live in a place that uses the Oxford Comma, then reading the second version, you cannot be sure whether Jack left the pub with two people (a policeman called John and Simon) or three people (John, Simon, and a policeman).

Be aware though that not using an Oxford Comma can also introduce ambiguity for the same reason. Look at these two sentences:
  • Jack left the pub with the twins (Sarah and Janet).
  • Jack left the pub with the twins, Sarah and Janet.
Both are fine grammatically. However, if you live in a place that doesn't use the Oxford Comma, then reading the second version, you cannot be sure whether Jack left the pub with two people (twins called Sarah and Janet) or four people (Sarah, Janet, and the twins).

Clarity Trumps Convention Every Single Time

So, there are arguments for and against the Oxford Comma. As it happens, you probably don't have a choice whether to adopt the Oxford Comma. If you live in the UK, you probably shouldn't adopt it. If you live in the US, you probably should. Whatever convention you go for, be consistent. That is the only rule.

This is not a 100% rule, however. If your local convention means putting ambiguity into your writing, then break the convention to eliminate the ambiguity.

There is only one 100% rule when it comes to the Oxford Comma:
Clarity trumps convention.

An Infographic about Ambiguity with and without the Oxford Comma

Sometimes the Oxford Comma creates ambiguity. Sometimes it eliminates it. The same is true for not using an Oxford Comma.

Oxford Comma ambiguity

Why Should I Care about the Oxford Comma?

Be Consistent, But Break Convention for Clarity

Failing to use, or using, Oxford Commas could annoy your readers if you choose a different convention to them. So, if you're unsure what convention to follow, hunt down a few authoritative local texts and copy whatever convention they use.

Thinking about the Oxford Comma will help you to keep your text consistent. However, if you write something ambiguous, try to reword your sentence. If that proves too cumbersome, have the confidence to switch conventions in the same document. Above all, remember this: Clarity trumps both conventions.

Key Point

  • Find out what convention you're supposed to be using, and stick to it. If your local convention creates an ambiguous sentence, don't stick to it.

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See Also

Using commas (a summary) Try our commas test Using semicolons in lists Commas after a sentence introductions Commas after a transitional phrase Commas after interjections (yes, no, indeed) Commas before conjunctions (and, or, but) Commas for parenthesis Commas with a long subject Commas with numbers Commas with quotation (speech) marks Commas with the vocative case Commas with Dear, Hello, and Hi