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The 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.

With two items in a list, don't use a comma to separate the list items (unless it helps your reader). 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).
  • Bacon, eggs, and tomatoes ()
Those following "UK convention" should not use a comma.
  • Bacon, eggs and tomatoes ()
If breaking this convention makes the text clearer, then break convention. Clarity trumps both conventions.

A Page Dedicated to the 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. 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.

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 coordinate 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 with the conjunction that sits before the last list item. 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 they between The Embankment and Elephant and Castle? A "helping" 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 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.

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 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 are fine grammatically. However, if you live in a place that uses the Oxford Comma, when 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, when 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 or not. 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

Oxford comma before and
Sometimes the Oxford Comma creates ambiguity. Sometimes it eliminates it. The same is true for not using an Oxford Comma.
Top Tip

Be Consistent, But Break Convention for Clarity

Follow one of the conventions, and stick to it throughout your document. 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.