Commas in Lists (Grammar Lesson)

The Quick Answer

When there are two items in a list, don't use a comma to separate the list items (unless it helps your reader). If there are more than two list items, then those following US convention should use a comma before the conjunction (usually and or or).

Bread, milk, and cheese ()

Those following UK convention should not use a comma.

Bread, milk and cheese ()

If your organization advocates the so-called Oxford Comma, then use a comma. If you have a case when breaking convention makes the text clearer (and that could mean omitting or inserting the comma depending on which convention you're following), then break convention. Clarity trumps both conventions.

Using Commas in Lists

When there are two items in a list, there is no need to separate the list items with a comma. For example:

Bread and cheese
London and New York

The last item in a list is usually preceded by a conjunction. The two most commonly seen in lists are and and or. (The conjunction and features in both examples above.)

When there are more than two items, the situation gets more complicated. Generally speaking, in the UK, writers tend not put a comma before the conjunction. In the US, however, writers tend to use a comma.

This delineation between UK and US is very general — there are plenty of organizations in both countries that do not adhere to this.

The Oxford Comma

When a comma is used before the conjunction in a list, it is known as an Oxford Comma. Some people (mostly, but not exclusively, Brits) consider the Oxford Comma to be a waste of ink, while others (mostly, but not exclusively, Americans) strongly campaign for its inclusion. There really is no rule. 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.)

Bread, milk and cheese ( or those who don't use the Oxford Comma)
Bread, milk, and cheese ( or those who do use the Oxford Comma)
London, Paris and New York ( or those who don't use the Oxford Comma)
London, Paris and New York ( or those who do use the Oxford Comma)

Followers of the Oxford Comma (generally Americans)	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.	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.

There is another consideration. Sometimes, it is appropriate to break whatever convention you're following for the sake of clarity — even in a list with just two list items. For example:

The news will be shown after Dangermouse, and Rug Rats.

Dangermouse and Rug Rats

The train will stop at Harrow, Pinner, Watford, and Bushey.

Watford and Bushey

Bath and Wells

The emblem is an amalgamation of the British and Irish flags, the Stars and Stripes, and the Hammer and Sickle.

and

Using Lots of Adjectives (Enumeration of Adjectives)

Especially in creative writing, there is a need to use several adjectives. The rules about using commas in a list of adjectives are far more relaxed. For example:

For TWO adjectives:

vast, inhospitable moor (with a comma)
vast and inhospitable moor (with and)
vast inhospitable moor (with nothing)

For THREE or more adjectives:

vast, inhospitable, windy moor (commas between)
vast, inhospitable and windy moor
(comma(s) between and then and )

and

Oxford Comma

vast inhospitable windy moor (nothing between)
vast inhospitable and windy moor (nothing and then and)

In short, you cannot go wrong with two adjectives and using three is rare. (Lining up adjectives in a row is called enumeration of adjectives.)

Beware Confusion with an Oxford Comma

Commas can be used to introduce additional information (called parenthesis). For example:

My friend, Simon, lives near the concrete cows in Milton Keynes.

My friend

So, when a comma is used before a conjunction in a list, it could make the list item before the comma look like a parenthesis. This could create confusion. For example:

I left the pub with my friend, Simon, and Terry.

I left the pub with my friend, Simon and Terry.

That said, the Oxford Comma is not usually accused of creating ambiguity. It usually makes the list items easier to see, especially when the list items themselves contain conjunctions.

On the London Underground, the Bakerloo Line goes through Harrow and Wealdston, Paddington, Oxford Circus, and Elephant and Castle.
On the London Underground, the Bakerloo Line goes through Harrow and Wealdston, Paddington, Oxford Circus and Elephant and Castle.

With the Oxford Comma omitted (i.e., the second example above), those unfamiliar with London might think that "Oxford Circus and Elephant" was one station. Also, look at this:

The Bakerloo Line runs between Harrow and Wealdstone, and Elephant and Castle.
The Bakerloo Line runs between Harrow and Wealdstone and Elephant and Castle.

The first example (with the Oxford Comma) is far clearer.

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.

Read more about the Oxford Comma.

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