Serial comma

In English language punctuation, a serial comma, or series comma (also called an Oxford comma or Harvard comma), is a comma placed immediately after the penultimate term (i.e. before the coordinating conjunction [usually "and" or "or"]) in a series of three or more terms. For example, a list of three countries might be punctuated either as "France, Italy and Spain" (without the serial comma) or "France, Italy, and Spain" (with the serial comma).
Opinions among writers and editors differ on whether to use the serial comma, and usage also differs somewhat between regional varieties of English. British English allows constructions with or without this comma, while in American English it is common and sometimes even considered mandatory to use the comma. A majority of American style guides mandate use of the serial comma, including APA style, "The Chicago Manual of Style", "Garner's Modern American Usage", "The MLA Style Manual", Strunk and White's "The Elements of Style", and the "U.S. Government Printing Office Style Manual". By contrast, the "Associated Press Stylebook" advises against it. In Canada, the stylebook published by The Canadian Press advises against it. Most British style guides do not mandate its use. "The Economist Style Guide" notes that most British writers use it only where necessary to avoid ambiguity. However, a few British style guides mandate it, most notably "The Oxford Style Manual".
"The Oxford Companion to the English Language" notes: "Usage varies as to the inclusion of a comma before "and" in the last item. ... This practice is controversial and is known as the serial comma or Oxford comma, because it is part of the house style of Oxford University Press." There are cases in which the use of the serial comma can avoid ambiguity and also instances in which its use can introduce ambiguity.
Arguments for and against.
Common arguments "for" consistent use of the serial comma:
Common arguments "against" consistent use of the serial comma:
Many sources are against both systematic use and systematic avoidance of the serial comma, making recommendations in a more nuanced way (see #Recommendations by style guides and subsequent sections).
Ambiguity.
Resolving ambiguity.
Omitting the serial comma may create ambiguity. Writers who normally avoid the serial comma often use one when it avoids ambiguity. Consider this apocryphal book dedication:
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:
But lists can also be written in other ways that eliminate the ambiguity without introducing the serial comma, such as by changing the word order or by using other punctuation, or none, to introduce or delimit them (though the emphasis may thereby be changed):
An example collected by Nielsen Hayden was found in a newspaper account of a documentary about Merle Haggard:
A serial comma following "Kris Kristofferson" would help prevent this being understood as Kris Kristofferson and Robert Duvall being the ex-wives in question.
Another example is:
It is unclear whether the eggs are being grouped with the bacon or the toast. Adding a serial comma removes this ambiguity:
Creating ambiguity.
In some circumstances using the serial comma can create ambiguity. If the book dedication above is changed to
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).
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 still be mistaken for a demigod, although he would be precluded from being a dildo collector.
Or consider
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:
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:
In general.
Ambiguities can often be resolved by the selective use of semicolons instead of commas; this is sometimes called the "super comma" function of semicolons.
Recommendations by style guides.
Lynne Truss writes: "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."
Omitting a serial comma is often characterized as a journalistic style of writing, as contrasted with a more academic or formal style. Journalists typically do not use the serial comma, possibly for economy of space. In Australia, Canada and South Africa, the serial comma tends not to be used in non-academic publications unless its absence produces ambiguity.
It is important that usage within a document be consistent; inconsistent usage can seem unprofessional.
Individual disputes.
Maine labor dispute.
In the U.S. state of Maine, the lack of a serial comma became the deciding factor in a $13 million lawsuit filed in 2014 that was eventually settled for $5 million in 2017. As the U.S. appeals judge David Barron wrote, "For want of a comma, we have this case."
In the case known as "O'Connor v. Oakhurst Dairy", a federal court of appeals was required to interpret a statute under which the "canning, processing, preserving, freezing, drying, marketing, storing, packing for shipment or distribution" of certain goods were activities exempted from the general requirement of overtime pay; the question was whether this list included the distribution of the goods, or only the packing of the goods for distribution. The lack of a comma suggested one meaning, while the omission of the conjunction "or" before "packing" and the fact that the "Maine Legislative Drafting Manual" advised against use of the serial comma suggested another. It said "Although authorities on punctuation may differ, when drafting Maine law or rules, don’t use a comma between the penultimate and the last item of a series." In addition to the absence of a comma, the fact that the word chosen was "distribution" rather than "distributing" was also a consideration, as was the question of whether it would be reasonable to consider the list to be an asyndetic list (a list in which the coordinating conjunction is absent). Truck drivers demanded overtime pay, and the defense conceded that the expression was ambiguous, but said it should be interpreted as exempting distribution activity from overtime pay. The district court agreed with the defense and held that "distribution" was an exempt activity. On appeal, however, the First Circuit decided that the sentence was ambiguous and "because, under Maine law, ambiguities in the state's wage and hour laws must be construed liberally in order to accomplish their remedial purpose", adopted the drivers' narrower reading of the exemption and ruled that those who distributed the goods were entitled to overtime pay. Oakhurst Dairy settled the case by paying $5 million to the drivers, and the phrase in the law in question was later changed to use serial semicolons and "distributing" resulting in "canning; processing; preserving; freezing; drying; marketing; storing; packing for shipment; or distributing".
The opinion in the case said that 43 of the 50 U.S. states had mandated the use of a serial comma and that both chambers of the federal congress had warned against omitting it, in the words of the U.S. House Legislative Counsel's Manual on Drafting Style, "to prevent any misreading that the last item is part of the preceding one"; only seven states "either do not require or expressly prohibited the use of the serial comma".
British 50p Brexit coin.
The new United Kingdom 50p coin commemorating Brexit day, 31 January 2020, was minted with the phrase "Peace, prosperity and friendship with all nations". English novelist Sir Philip Pullman and others criticized the omission of the Oxford comma, whilst others said it was an Americanism and not required in this instance.