From Wikipedia, the free encyclopedia
The serial comma (also known as the Oxford comma or Harvard comma) is the comma used immediately before a grammatical conjunction (nearly always and or or) that precedes the last item in a list of three or more items. The phrase "ham, chips, and eggs" is an example that is written with the serial comma, while "ham, chips and eggs" is identical in meaning, but does not include the serial comma.
Copy editors and others disagree on the use of the serial comma. It is nearly standard use in American English, but much less common in British English  (see extended treatment of this below, including a survey of published recommendations in Usage and subsequent sections). The serial comma is not used in Dutch, French, German, Russian, Spanish, or other main Indo-European languages.
Arguments typically advanced for use of the serial comma by default include:
- that it better matches the spoken cadence of sentences;
- that it sometimes reduces ambiguity; and
- that its use matches practice with other means of separating items in a list (example: when semicolons are used to separate items, a semicolon is consistently included before the last item, even when and or or is present).
Arguments typically advanced for avoidance of the serial comma by default include:
- that it is against much conventional practice;
- that it may introduce ambiguity; and
- that it is redundant, since the and or the or serves by itself to mark the logical separation between the final two items.
Many sources, however, are against automatic use of the serial comma and make recommendations in a more nuanced way (again, see Usage and subsequent sections).
The terms "Oxford comma" and "Harvard comma" come from Oxford University Press and Harvard University Press, where use of the serial comma is the house style.
(The term "serial comma" is sometimes used to refer to any of the commas serving as separators in a list: but this usage is rare and old-fashioned and in this article the term is used only as defined above.)
Use of the serial comma can sometimes remove ambiguity. Consider an apocryphal book dedication:
- To my parents, Ayn Rand and God.
There is ambiguity about the writer's parentage, because Ayn Rand and God can be read as an apposition to my parents. A comma before and removes the ambiguity:
- To my parents, Ayn Rand, and God.
- My favourite types of sandwiches are pastrami, ham, cream cheese and jam and peanut butter.
According to the two most plausible interpretations of this sentence, four kinds of sandwich are listed. But it is uncertain which are the third and fourth kinds. Adding a serial comma removes this ambiguity. With a comma after jam, the kinds of sandwich are these:
- cream cheese and jam
- peanut butter
With a comma after cream cheese, the kinds of sandwich are these:
- cream cheese
- jam and peanut butter
Some writers who normally avoid the serial comma may use one in these circumstances. Sometimes re-ordering the elements of such a list can help also.
Use of the serial comma can introduce ambiguity. "Betty, a maid and a rabbit" is clearly two people and a rabbit, whereas "Betty, a maid, and a rabbit" may be either one person (Betty, who is a maid) or two people (Betty and a maid), and a rabbit.
A similar example would be a book dedication which read "To my mother, Ayn Rand and God". With no serial comma this is unambiguous, but introducing one creates ambiguity about the writer's mother, because "Ayn Rand" can then be read as an apposition to "my mother".
The Times once published  a description of a Peter Ustinov documentary: "highlights of his global tour include encounters with Nelson Mandela, an 800-year-old demigod and a dildo collector." This is ambiguous as it stands, but even with a serial comma Mandela could still be mistaken for a demigod.
Or consider "They went to Oregon with Betty, a maid, and a cook." The presence of the last comma creates the possibility that Betty is a maid, reasonably allowing it to be read either as a list of two people or as a list of three people, context aside. On the other hand, removing the comma leaves the possibility that Betty is both a maid and a cook, so in this case neither the use nor the avoidance of the serial comma resolves the ambiguity.
A writer who intends for Betty, the maid, and the cook to be three distinct people may create an ambiguous sentence regardless of whether the serial comma is adopted. Furthermore, if the reader is unaware of which convention is being used, both versions are always ambiguous.
These forms (among others) would remove the ambiguity:
- They went to Oregon with Betty – a maid and a cook. (One person)
- They went to Oregon with Betty, who is a maid and a cook. (One person)
- They went to Oregon with Betty (a maid) and a cook. (Two people)
- They went to Oregon with Betty – a maid – and a cook. (Two people)
- They went to Oregon with the maid Betty and a cook. (Two people)
- They went to Oregon with Betty and a maid and a cook. (Three people)
- They went to Oregon with a full staff: Betty; a maid; and a cook. (Three people)
- They went to Oregon with a maid, a cook, and Betty. (Three people)
- They went to Oregon with a maid, a cook and Betty. (Three people)
In general, the three-item list "x, y and z" is unambigious if "y and z" cannot be interpreted as an apposition to x. Equally, "x, y, and z" is unambigious if y cannot be interepred as an apposition. If neither "y" nor "y and z" can be appositions to x, then both alternatives are unambigious. If both can be appositions, then both alternatives are ambigious.
The Chicago Manual of Style, Strunk and White's Elements of Style, most authorities on American English and Canadian English, and some authorities on British English – for example, Oxford University Press and Fowler's Modern English Usage – recommend the use of the serial comma. Newspaper style guides – such as those published by The New York Times, the Associated Press, The Times newspaper in the United Kingdom, and the Canadian Press – recommend against it, possibly for economy of space.
In Australia, the United Kingdom, and South Africa, the serial comma tends not to be used in non-academic publications unless its absence produces ambiguity. Many academic publishers (e.g. Cambridge University Press) also avoid it, though some academic publishing houses in these countries do use it. The Australian Government Publishing Service's Style Manual for Authors, Editors and Printers recommends against it.
Style guides supporting mandatory use
The following American style guides support mandatory use of serial comma:
- The United States Government Printing Office's Style Manual:
After each member within a series of three or more words, phrases, letters, or figures used with and, or, or nor.
- "red, white, and blue"
- "horses, mules, and cattle; but horses and mules and cattle"
- "by the bolt, by the yard, or in remnants"
- "a, b, and c"
- "neither snow, rain, nor heat"
- "2 days, 3 hours, and 4 minutes (series); but 70 years 11 months 6 days (age)"
- Wilson Follett's Modern American Usage: A Guide (Random House, 1981), pp. 397-401:
What, then, are the arguments for omitting the last comma? Only one is cogent – the saving of space. In the narrow width of a newspaper column this saving counts for more than elsewhere, which is why the omission is so nearly universal in journalism. But here or anywhere one must question whether the advantage outweighs the confusion caused by the omission ...
The recommendation here is that [writers] use the comma between all members of a series, including the last two, on the common-sense ground that to do so will preclude ambiguities and annoyances at a negligible cost." 
- Chicago Manual of Style, 15th edition (University of Chicago Press, 1993) Chapter 5.5:
In a series consisting of three or more elements, the elements are separated by commas. When a conjunction joins the last two elements in a series, a comma is used before the conjunction ...
- "Attending the conference were Farmer, Johnson, and Kendrick.
- "We have a choice of copper, silver, or gold." 
- The American Medical Association Manual of Style, 9th edition (1998) Chapter 6.2.1:
Use a comma before the conjunction that precedes the last term in a series.
- Outcomes result from a complex interaction of medical care and genetic, environmental, and behavioral factors.
- The physician, the nurse, and the family could not convince the patient to take his medication daily.
- While in the hospital, these patients required neuroleptics, maximal observation, and seclusion.
- The Publication Manual of the American Psychological Association, 5th edition (2001) Chapter 3.02:
Use a comma between elements (including before and and or) in a series of three or more items.
- the height, width, or depth
- in a study by Stacy, Newcomb, and Bentler
The Elements of Style:
In a series of three or more terms with a single conjunction, use a comma after each term except the last.
Style guides opposing mandatory use
- The Times style manual:
Avoid the so-called Oxford comma; say 'he ate bread, butter and jam' rather than 'he ate bread, butter, and jam'." 
- The Economist style manual:
Do not put a comma before and at the end of a sequence of items unless one of the items includes another and. Thus 'The doctor suggested an aspirin, half a grapefruit and a cup of broth. But he ordered scrambled eggs, whisky and soda, and a selection from the trolley.' 
- The AP Stylebook:
Use commas to separate elements in a series, but do not put a comma before the conjunction in a simple series: The flag is red, white and blue. He would nominate Tom, Dick or Harry.
Put a comma before the concluding conjunction in a series, however, if an integral element of the series requires a conjunction: I had orange juice, toast, and ham and eggs for breakfast.
Use a comma also before the concluding conjunction in a complex series of phrases: The main points to consider are whether the athletes are skillful enough to compete, whether they have the stamina to endure the training, and whether they have the proper mental attitude.
- The Australian Government Publishing Service's Style Manual for Authors, Editors and Printers:
A comma is used before and, or, or etc. in a list when its omission might either give rise to ambiguity or cause the last word or phrase to be construed with a preposition in the preceding phrase: "There were many expeditions, including those of Sturt, Mitchell, Burke and Wills, and Darling." "The long days at work, the nights of intense study, and inadequate food eventually caused them serious health problems." "The sea, the perfume of wisteria, or a summer lunch: any of these revived memories of an easier time." "We needed to know how to get there, what time to get there, the number of participants, etc."
Generally, however, a comma is not used before and, or or etc. in a list: "John, Warren and Peter came to dinner." "Fruit, vegetables or cereals may be substituted." "Why not hire your skis, boots, overpants etc.?"
- The Guardian Style Guide:
a comma before the final "and" in lists: straightforward ones (he ate ham, eggs and chips) do not need one, but sometimes it can help the reader (he ate cereal, kippers, bacon, eggs, toast and marmalade, and tea)
New Zealand poet Elizabeth Smither has written a poem about the serial comma , and there is a musical band called Oxford Comma. 
- Wikipedia:Manual of Style#Serial commas Wikipedia's policy on serial commas.
- Style Manual 29th edition, U.S. Government Printing Office (Washington, 2003)
- The Economist style guide on commas
- The Times style guide on punctuation
- The Case of the Serial Comma, The Professional Training Company
- Oxford comma, a poem by Elizabeth Smither
- The Chicago Manual of Style: The Essential Guide for Writers, Editors, and Publishers, 15th edition, Chicago University Press, (Chicago, 2003) ISBN 0-226-10403-6
- Follett, W. (New York, 1981) Modern American Usage Random House Value Publishing, ISBN 0-517-33508-5
- H. W. Fowler and R.W. Burchfield (Oxford, 2000) The New Fowler's Modern English Usage, third edition, Oxford University Press, ISBN 0-19-860263-4
- Truss, L. (London, 2003) Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation, Profile Books, ISBN 1-86197-612-7
- ^ 
- ^ 
- ^ "Planet Ustinov", Nov 22, 1998
- Rules governing comma usage
- Wikicities essay on the serial comma