Commas in Lists
The Quick AnswerCommas are used to separate list items. Here is an overview of the rules determining when to use a comma.
Commas with Two List ItemsWhen there are two items in a list, don't use a comma to separate the list items (unless it helps your reader). For example:
- Please buy bread and milk.
- Please buy custard, and banana muffins. (Without the comma, "custard and banana muffins" could be one item. The comma helps the reader.)
Commas with More Than Two List ItemsIf there are more than two list items, those following US convention should use a comma before the conjunction (usually "and" or "or").
- Please buy bread, milk, and cheese ()
- Please buy bread, milk and cheese ()
Break the Rule for ClarityIf breaking your "national" 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. (There's more on this below.)
Commas in ListsWhen 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
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 a general observation. There are plenty of organizations in both countries that do not adhere to these "national" conventions.
The Oxford CommaWhen 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)
Summary of Commas in ListsThis table summarizes how commas are used in lists:
|Followers of the Oxford Comma
|Avoiders of the Oxford Comma|
Break Convention for ClarityThere 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. (Without the comma, people could think that "Dangermouse and Rug Rats" is one programme.)
- The train will stop at Harrow, Pinner, Watford, and Bushey. ("Watford and Bushey" could be one place, like "Bath and Wells.")
- The emblem is an amalgamation of the British and Irish flags, the Stars and Stripes, and the Hammer and Sickle. (The word "and" appears lots of times in this example. The comma before the "and" makes it easier for the reader to identify the last list item.)
Beware of Creating Ambiguity with Your CommaCommas can be used to introduce additional information (called parenthesis). For example:
- My friend, Simon, joined the circus as a clown. (In this example, commas are being used to add information about "my friend.")
- I left the house with my friend, Simon, and Terry. (With this sentence (with an Oxford Comma), it is unclear whether I left the house with two people (1) My friend Simon and (2) Terry or three people (1) my unnamed friend, (2) Simon, and (3) Terry.)
- I left the house with my friend, Simon and Terry. (With this sentence (without the Oxford Comma), there is no ambiguity. It must be three people.)
- I left the house with the twins, Sarah and Jack. (With this sentence (without an Oxford Comma), it is unclear whether I left the house with two people (1 + 2) twins called Sarah and Jack or four people (1 + 2) some unnamed twins, (3) Sarah, and (4) Jack.)
- I left the house with the twins, Simon, and Terry. (With this sentence (with an Oxford Comma), there is no ambiguity. It must be four people.)
- On the London Underground, the Bakerloo Line goes through Harrow and Wealdston, Paddington, Oxford Circus, and Elephant and Castle. (This list with an Oxford Comma is clearer than the list below.)
- 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.)
- The Bakerloo Line runs between Harrow and Wealdstone, and Elephant and Castle. (This is clearer.)
- The Bakerloo Line runs between Harrow and Wealdstone and Elephant and Castle.
Be Consistent – but Break Convention for ClarityFollow 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.