In punctuation, a serial comma or series comma (also called Oxford comma and Harvard comma) is a comma placed immediately before the coordinating conjunction (usually and, or, or nor) in a series of three or more terms. For example, a list of three countries might be punctuated either as "Portugal, Spain, and France" (with the serial comma), or as "Portugal, Spain and France" (without the serial comma).
Opinions among writers and editors differ on whether to use the serial comma. In American English, a majority of style guides mandate use of the serial comma, including The Chicago Manual of Style, Strunk and White's Elements of Style, and the U.S. Government Printing Office Style Manual. The Associated Press Stylebook for journalistic writing advises against it. It is used less often in British English, but some British style guides require it, including the Oxford University Press's style manual and Fowler's Modern English Usage. Some writers of British English use it only where necessary to avoid ambiguity.
Arguments for and against 
Common arguments for consistent use of the serial comma:
- Use of the comma is consistent with conventional practice.
- It matches the spoken cadence of sentences better.
- It can resolve ambiguity (see examples below).
- Its use is consistent with other means of separating items in a list (for example, when semicolons are used to separate items a semicolon is consistently included before the last item even when and or or is present).
- Its omission can suggest a stronger connection between the last two items in a series than actually exists.
Common arguments against consistent use of the serial comma:
- Use of the comma is inconsistent with conventional practice.
- The comma may introduce ambiguity (see argument #3 and examples below).
- It is redundant in a simple list because the and or the or is often meant to serve (by itself) to mark the logical separation between the final two items unless the final two items are not truly separate items but are two parts of a compound single item.
- Where space is at a premium the comma adds unnecessary bulk to the text.
Many sources are against both systematic use and systematic avoidance of the serial comma, making recommendations in a more nuanced way (see Usage and subsequent sections).
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Resolving ambiguity 
- To my parents, Ayn Rand and God.
There is ambiguity about the writer's parentage, because Ayn Rand and God can be read as in apposition to my parents, leading the reader to believe that the writer claims Ayn Rand and God are the parents. A comma before and removes the ambiguity:
- To my parents, Ayn Rand, and God.
But appositions can also be written in other ways that eliminate the ambiguity without introducing the serial comma, such as using other punctuation, or none, to introduce or delimit them. For example, in the following manner:
- To God, Ayn Rand and my parents.
An example collected by Nielsen Hayden was found in a newspaper account of a documentary about Merle Haggard:
- Among those interviewed were his two ex-wives, Kris Kristofferson and Robert Duvall.
- Among those interviewed were his two ex-wives, Kris Kristofferson, and Robert Duvall.
- My usual breakfast is coffee, bacon and eggs and toast.
It is uncertain whether bacon and eggs, or eggs and toast, should be grouped together. Adding a serial comma removes this ambiguity. With a comma after eggs, the foods are:
- Bacon and eggs
With a comma after bacon:
- Eggs and toast
Writers who normally avoid the serial comma often use one in these circumstances, though sometimes re-ordering the elements of such a list can help as well.
Creating ambiguity 
In some circumstances the serial-comma convention can introduce ambiguity. An example is a dedication reading:
- To my mother, Ayn Rand, and God
The serial comma after Ayn Rand creates ambiguity about the writer's mother because it uses punctuation identical to that used for an appositive phrase, leaving it unclear whether this is a list of three entities (1, my mother; 2, Ayn Rand; and 3, God) or of only two entities (1, my mother, who is Ayn Rand; and 2, God). Without a serial comma, the above dedication would read: To my mother, Ayn Rand and God, a phrase ambiguous only if the reader is prepared to accept the unlikely interpretation my mother, who is both Ayn Rand and God. Other ways of eliminating the ambiguity are possible; for instance, additional prepositions could be used (To my mother, to Ayn Rand, and to God) or the order could be reversed (To my mother, God, and Ayn Rand).
Unresolved ambiguity 
The Times once published an unintentionally humorous description of a Peter Ustinov documentary, noting that "highlights of his global tour include encounters with Nelson Mandela, an 800-year-old demigod and a dildo collector". This would still be ambiguous if a serial comma were added, as Mandela could then be mistaken for a demigod, although he would be precluded from being a dildo collector.
- They went to Oregon with Betty, a maid, and a cook.
This is ambiguous because it is unclear whether "a maid" is an appositive describing Betty, or the second in a list of three people. On the other hand, removing the final comma:
- They went to Oregon with Betty, a maid and a cook.
leaves the possibility that Betty is both a maid and a cook (with "a maid and a cook" read as a unit, in apposition to Betty). So in this case neither the serial-comma style nor the no-serial-comma style resolves the ambiguity. A writer who intends a list of three distinct people (Betty, maid, cook) 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:
- 1 person
- They went to Oregon with Betty, who was a maid and a cook.
- They went to Oregon with Betty, both a maid and a cook.
- 2 persons
- They went to Oregon with Betty (a maid) and a cook.
- They went to Oregon with Betty—a maid—and a cook.
- They went to Oregon with Betty, a maid, and with a cook.
- They went to Oregon with the maid Betty and a cook.
- They went to Oregon with a cook and Betty, a maid.
- They went to Oregon with Betty, a maid; and a cook.
- 3 persons
- They went to Oregon with Betty, as well as a maid and a cook.
- They went to Oregon with Betty and a maid and a cook.
- They went to Oregon with Betty, one maid and a cook.
- They went to Oregon with a maid, a cook, and Betty.
In general 
- The list x, y and z is unambiguous if y and z cannot be read as in apposition to x.
- Equally, x, y, and z is unambiguous if y cannot be read as in apposition to x.
- If neither y nor y[,] and z can be read as in apposition to x, then both forms of the list are unambiguous; but if y or y[,] and z can be read as in apposition to x, then both forms of the list are ambiguous.
- x and y and z is unambiguous.
The Chicago Manual of Style, Strunk and White's Elements of Style, the United States Government Printing Office, 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 or require the use of the serial comma. Newspaper style guides (such as those published by The New York Times, The Los Angeles Times, the Associated Press, The Times newspaper in the United Kingdom, and the Canadian Press) recommend against it, possibly for economy of space.
The differences of opinion on the use of the serial comma are well characterized by Lynne Truss in her popularized style guide Eats, Shoots & Leaves: "There are people who embrace the Oxford comma, and people who don't, and I'll just say this: never get between these people when drink has been taken."
In Australia, Canada, South Africa, and the United Kingdom, the serial comma tends not to be used in non-academic publications unless its absence produces ambiguity. The Australian Government Publishing Service's Style Manual for Authors, Editors and Printers (6th edition, 2002) recommends against it, except "to ensure clarity" (p. 102).
Style guides supporting mandatory use 
The following style guides support mandatory use of the 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, nor 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.
- The Chicago Manual of Style, 15th edition (University of Chicago Press, 2003), paragraph 6.19
When a conjunction joins the last two elements in a series, a comma ... should appear before the conjunction. Chicago strongly recommends this widely practiced usage....
- "She took a photograph of her parents, the president, and the vice president."
- "I want no ifs, ands, or buts."
- "The meal consisted of soup, salad, and macaroni and cheese."
- The Elements of Style (Strunk and White, 4th edition 1999), Rule 2
In a series of three or more terms with a single conjunction, use a comma after each term except the last.
- For example, "red, white, and blue."
- 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, 6th edition (2010) Chapter 4.03
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 Oxford Style Manual, 2002, Chapter 5, section 5.3 Comma
For a century it has been part of OUP style to retain or impose this last serial (or series) comma consistently, [...] but it is commonly used by many other publishers both here and abroad, and forms a routine part of style in US and Canadian English. [...] Given that the final comma is sometimes necessary to prevent ambiguity, it is logical to impose it uniformly, so as to obviate the need to pause and gauge each enumeration on the likelihood of its being misunderstood – especially since that likelihood is often more obvious to the reader than the writer. (pp. 121–122)
- The CSE Manual for Authors, Editors, and Publishers (Council of Science Editors, 7th edition, 2006), Section 126.96.36.199
To separate the elements (words, phrases, clauses) of a simple series of more than 2 elements, including a comma before the closing “and” or “or” (the so-called serial comma). Routine use of the serial comma helps to prevent ambiguity.
- Garner's American Usage (Oxford, 2003)
Whether to include the serial comma has sparked many arguments. But it's easily answered in favor of inclusion because omitting the final comma may cause ambiguities, whereas including it never will.
- MLA Style Manual and Guide to Scholarly Publishing (Modern Language Association 2008), paragraph 3.4.2.b
Use commas to separate words, phrases, and clauses in a series.
In an enumeration of three or more items, the practice in MHRA journals is to insert commas after all but the last item, to give equal weight to each enumerated element:
- "The University has departments of French, German, Spanish, and Portuguese within its Faculty of Arts."
The conjunctions and and or without a preceding comma are understood as linking the parts of a single enumerated element:
- "The University has departments of French, German, Spanish and Portuguese, Czech and Polish, and Dutch."
- "Comedians such as Laurel and Hardy, Abbott and Costello, or Charlie Chaplin."
Most college writing handbooks in the U.S. also advocate use of the serial comma.
Style guides opposing mandatory use 
Avoid the so-called Oxford comma; say "he ate bread, butter and jam" rather than "he ate bread, butter, and jam".
In general, do not use a comma before and or or in a series: The snow stalled cars, buses and trains.
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."
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.?"
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), and sometimes it is essential:
I dedicate this book to my parents, Martin Amis, and JK Rowling
withI dedicate this book to my parents, Martin Amis and JK Rowling
- University of Oxford Public Affairs Directorate Writing and Style Guide
Note that there is generally no comma between the penultimate item and ‘and’/‘or’ – this is sometimes referred to as the ‘Oxford comma’. However, it is essential to use an Oxford comma if required to prevent ambiguity:
The comma after the penultimate item may be omitted in books published by the MHRA, as long as the sense is clear.
In British practice there's an Oxford/Cambridge divide … In Canada and Australia the serial comma is recommended only to prevent ambiguity or misreading.
Other languages 
In the following languages, the serial comma is not the norm and may go against punctuation rules:
- The terms Oxford comma and Harvard comma come from Oxford University Press and Harvard University Press, where serial-comma use is the house style.
- Sometimes, the term also denotes the comma that might come before etc. at the end of a list (see the Australian Government Publishing Service's Style Manual for Authors, Editors, and Printers, below). Such an extension is reasonable, since etc. is the abbreviation of the Latin phrase et cetera (lit. and other things).
- The serial comma sometimes refers to any of the separator commas in a list, but this is a rare, old-fashioned usage. Herein, the term is used only as defined above.
- Strunk, Jr., William; White, E. B. (2005). The Elements of Style. Illustrated by Maira Kalman (Illustrated ed.). Penguin Press. p. 3. ISBN 9781594200694. Retrieved February 15, 2013. "In a series of three or more terms with a single conjunction, use a comma after each term except the last."
- Truss, Lynn (2004). Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation. New York: Gotham Books. p. 84. ISBN 1-59240-087-6.
- The Oxford Style Manual, 2002: "The presence or lack of a comma before and or or ... has become the subject of much spirited debate. For a century it has been part of OUP style ..., to the extent that the convention has come to be called the 'Oxford comma'. But it is commonly used by many other publishers here and abroad, and forms a routine part of style in US and Canadian English" (p. 121).
- The Economist Style Guide (10th ed.). Profile Books. 2012. pp. 152–153. ISBN 978-1-84668-606-1.
- The Oxford Style Manual, 2002: "But it is commonly used by many other publishers here and abroad, and forms a routine part of style in US and Canadian English" (p. 121).
- The Oxford Style Manual, 2002; from discussion of the serial comma: "If the last item in a list has emphasis equal to the previous ones, it needs a comma to create a pause of equal weight to those that came before" (p. 121). The University of Oxford itself is quite distinct from Oxford University Press, and gives different advice. See University of Oxford Writing and Style Guide, below in this article.
- The Oxford Style Manual, 2002; from discussion of the serial comma: "The last comma serves also to resolve ambiguity, particularly when any of the items are compound terms joined by a conjunction" (p. 122).
- The Oxford Style Manual, 2002; in discussion of the semicolon, examples are given in which complex listed items are separated by semicolons, with the same structure and on the same principles as are consistently recommended for use of the comma as a list separator in the preceding section (pp. 124–5)
- "Rhetorical Grammar: Grammatical Choices, Rhetorical Effects. 4th Ed.", 2003; This punctuation style, however, does have a drawback: It may imply a closer connection than actually exists between the last two elements of the series (p. 89)
- Ridout, R., and Witting, C., The Facts of English, Pan, 1973, p. 79: "Usually in such lists 'and' is not preceded by a comma, [...]".
- Implicit in the treatment given in The Australian Government Publishing Service's Style Manual for Authors, Editors and Printers, 6th edition, Wiley, 2002, on p. 102. The exception discussed (see Usage, below) makes sense only on the assumption of this argument.
- Nielsen Hayden, Teresa (1994). Making Book. Framingham, Massachusetts: The NESFA Press. p. 143.
- "Making Light". Nielsenhayden.com. October 21, 2010. Retrieved February 10, 2013.
- J. Hankin, Susan. Statutory Interpretation in the Age of Grammatical Permissiveness: An Object Lesson for Teaching Why Grammar Matters. Perspectives, Vol. 18, No. 2, Winter 2010. "Interestingly, [this] example has been cited in Wikipedia’s discussion of the serial comma debate to illustrate when including a serial comma can sometimes create ambiguity (and while part of me cringes at the thought of citing Wikipedia, this example is too good to pass up)."
- "Planet Ustinov", Nov 22, 1998
- Bryan A. Garner (2003). Garner's Modern American Usage. New York: Oxford University Press. p. 654. ISBN 0-19-516191-2.
- Lynne Truss (2004). Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation. Gotham. ISBN 1-59240-087-6.
- "8. Punctuation" (PDF). GPO Style Manual (30th ed.). Washington, DC: U.S. Government Printing Office. 2008. p. 201 §8.42. ISBN 978-0-16-081813-4. Retrieved June 9, 2010.
- "The Case of the Serial Comma-Solved!". Swcp.com. Retrieved February 10, 2013.
- MHRA Style Guide: a handbook for authors, editors, and writers of theses (3rd ed.). London: Modern Humanities Research Association. 2013. pp. 33–4. ISBN 978-1-78188-009-8.
- Andy Gramlich, "Commas: the biggest little quirks in the English language", Hohonu 2005, Volume 3, Number 3. http://www.uhh.hawaii.edu/academics/hohonu/writing.php?id=82
- Kelly, Jeremy (December 16, 2005). "Online Style Guide – P". London: The Times. pp. (see punctuation/commas). Retrieved March 22, 2008.
- Perlman, Merrill (March 6, 2007). Talk to the Newsroom: Director of Copy Desks Merrill Perlman. The New York Times
- "Style Guide". The Economist. Retrieved 19 April 2013.
- Norman Goldstein, ed. (2002). The Associated Press Stylebook and Briefing on Media Law. Cambridge, Massachusetts: Perseus. pp. 329–330. ISBN 0-7382-0740-3.
- "Guardian and Observer style guide: O". The Guardian (London). December 19, 2008. Retrieved April 1, 2010.
- "Punctuation – University of Oxford". Public Affairs, University of Oxford. Retrieved June 1, 2012.
- Peters, Pam (2004). The Cambridge Guide to English Usage. Cambridge, England: Cambridge University Press. ISBN 0-521-62181-X.
- Dansk Sprognævn (2004). "Kommaregler" (PDF) (in Danish). pp. 8–10. Retrieved December 16, 2011.| The given examples are inconsistent as to the use of the serial comma.
- Nederlandse Taalunie. "Komma voor en" (in Dutch). Retrieved March 16, 2012.
- Korpela, Jukka. "Pilkku: Pilkku luettelon osien erottimena". Nykyajan kielenopas (in Finnish). Retrieved August 18, 2012.
- Grevisse, Maurice; revised by André Goosse (1988). "Ponctuation: la virgule dans la coordination". Le bon usage: grammaire française (in French) (12th ed.). Paris-Gembloux: Duculot. pp. §124 (c) Remarque 1. ISBN 2-8011-0588-0.
- Institut für Deutsche Sprache (IDS) Mannheim (2006). ""Deutsche Rechtschreibung. Regeln und Wörterverzeichnis" – Überarbeitetes Regelwerk (Fassung 2006)" (PDF) (in German). pp. § 72, p. 79. Retrieved March 12, 2009.
- "EUROPA – Δικτυακή Πύλη της Ευρωπαϊκής Ένωσης – Υπηρεσία Εκδόσεων – Εγχειρίδιο σύνταξης – IV. Συμβατικοί κανόνες για την ελληνική γλώσσα – 10. Οδηγίες για την παρουσίαση των κειμένων – 10.1.2 Κόμμα" (in Greek). Retrieved 2012-10.18.
- "יסודות כללי הפיסוק" (in Hebrew). Retrieved March 1, 2013.
- Accademia della Crusca. "Uso della virgola prima della congiunzione e" (in Italian). Retrieved December 24, 2012.
- "Kommaregler" (in Norwegian). Språkrådet. Retrieved June 27, 2012.
- Polański, E. (editor) (2006). Wielki słownik ortograficzny PWN z zasadami pisowni i interpunkcji, 2nd ed., Warsaw: Polish Scientific Publishers PWN. ISBN 978-83-01-14571-2.
- "Cu virgulă înainte de "și" | Opinii". Robintel.ro. Retrieved February 10, 2013.
- Real Academia Española (October 2005). "Diccionario panhispánico de dudas: coma² §1.2.1" (in Spanish). Retrieved March 20, 2007.