Commas in Lists

Commas in Lists When there are two items in a list, there is no need to separate the list items with a comma.  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 organisations 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. Examples: 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 Watford, 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.) Using Lots of Adjectives (Enumeration of Adjectives) Often in creative writing, there is a need to use several adjectives (describing words – see lesson 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 ) (With this style, follow your convention; i.e., put a comma before and if you advocate the 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 are used to introduce additional information (called parenthesis). For example: My friend, Simon, lives near the concrete cows in Milton Keynes. (In this example, commas are being used to add information about 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. (In this sentence, it is unclear whether I left the pub with two people (My friend Simon and Terry) or three people (my unnamed friend, Simon and Terry). I left the pub with my friend, Simon and Terry. (In this sentence (without the Oxford Comma), there is no ambiguity. It has to be three people.) 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 Wealdston, and Elephant and Castle. The Bakerloo Line runs between Harrow and Wealdston 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.

See also:

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
List of easily confused words 

Read more at http://www.grammar-monster.com/lessons/commas_in_lists.htm#DbbOoKm6OdFw21E0.99