Serial comma

Arguments for and against

Common arguments for consistent use of the serial comma:

1. Use of the comma is consistent with conventional practice.
2. It matches the spoken cadence of sentences better.
3. It can resolve ambiguity (see examples below).
4. 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).
5. 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:

1. Use of the comma is inconsistent with conventional practice.
2. The comma may introduce ambiguity (see examples below).
3. 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.
4. 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).

Resolving ambiguity

The style that always uses the serial comma may be less likely to result in ambiguity. Consider this apocryphal book dedication:

To my parents, Mother Teresa and the Pope.

There is ambiguity about the writer's parentage, because "Mother Teresa and the Pope" can be read as in apposition to my parents, leading the reader to believe that the writer claims Mother Teresa and the Pope are the parents. A comma before and removes the ambiguity:

To my parents, Mother Teresa, and the Pope.

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):

To the Pope, Mother Teresa 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.

A serial comma following "Kris Kristofferson" would help prevent this being understood as Kris Kristofferson and Robert Duvall being the ex-wives in question.

Consider also:

My usual breakfast is coffee, bacon and eggs and toast.

It is unclear whether the eggs are being grouped with the bacon or the toast. Adding a serial comma removes this ambiguity.

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 using the serial comma can create ambiguity. If the book dedication above is changed to

To my mother, Mother Teresa, and the Pope

the serial comma after Mother Teresa 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, Mother Teresa; and 3, the Pope) or of only two entities (1, my mother, who is Mother Teresa; and 2, the Pope). Without a serial comma, the above dedication would read: To my mother, Mother Teresa and the Pope, a phrase ambiguous only if the reader accepts the interpretation my mother, who is both Mother Teresa and the Pope.

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.

Or consider

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.

They went to Oregon with Betty, their maid and 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.

They went with Betty to Oregon with a maid and a cook.

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 both y and 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 if x and y and y and z cannot both be grouped.

Usage

In her style guide Eats, Shoots & Leaves, 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."

Journalists typically do not use the serial comma, possibly for economy of space. Journalistic 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 its use (see below).

The Chicago Manual of Style, Strunk and White's Elements of Style, and the United States Government Printing Office require the use of the serial comma. In Britain some authorities oppose its use, although others (for example, Oxford University Press and Fowler's Modern English Usage) do recommend it.

In Australia, Canada, and South Africa, 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).

Maine Labor Dispute

In a US court case in 2017, the court was required to interpret a rule that "The canning, processing, preserving, freezing, drying, marketing, storing, packing for shipment or distribution" of certain goods were activities not eligible for overtime pay; the question was whether this list included distribution of the goods, or only packing of the goods for distribution. The omission of the serial 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. The court 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. Thus, in this instance, it is implied that the fault lies in the absence of a serial comma; U.S. appeals judge David J. Barron wrote, "For want of a comma, we have this case."

Mainly American style guides supporting mandatory use

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." It notes that an age ("70 years 11 months 6 days") is not a series and should not take commas.

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, 16th edition (University of Chicago Press, 2010), paragraph 6.18

"When a conjunction joins the last two elements in a series of three or more, a comma ... should appear before the conjunction. Chicago strongly recommends this widely practiced usage." In answer to a reader's query, however, The Chicago Manual of Style Online qualifies this, saying "the serial comma is optional; some mainstream style guides (such as the Associated Press) don’t use it. ... there are times when using the comma (or omitting it) results in ambiguity, which is why it’s best to stay flexible."

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."

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."

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 CSE Manual for Authors, Editors, and Publishers (Council of Science Editors, 7th edition, 2006), Section 5.3.3.1

"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 Modern English Usage, 4th edition (Oxford University Press, 2016), "Punctuation," § D, "Comma", p. 748

"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—e.g.: "A and B, C and D, E and F[,] and G and H"."

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."

AAMT Book of Style for Medical Transcription

"Medical transcriptionists use the serial comma when two medications or diagnoses must be seen as separate; i.e., for "The patient was on Aspirin, Coversyl, and Dilaudid", the comma is used before "and" to avoid the reader erroneously thinking that Coversyl and Dilaudid must be taken together."

Mainly British style guides supporting mandatory use

The Oxford Style Manual, 2002

"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."

MHRA Style Guide (Modern Humanities Research Association), 3rd edition (2013)

"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 conjunctions and and or without a preceding comma are understood as linking the parts of a single enumerated element"

Mainly British 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 Guide

"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 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)."

MHRA Style Guide (Modern Humanities Research Association), 3rd edition (2013), paragraph 5.1

"The comma after the penultimate item may be omitted in books published by the MHRA, as long as the sense is clear."

The Cambridge Guide to English Usage

"In British practice there's an Oxford/Cambridge divide ... In Canada and Australia the serial comma is recommended only to prevent ambiguity or misreading."

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."

Mainly American style guides opposing mandatory use

The New York Times stylebook

"In general, do not use a comma before and or or in a series."

The AP Stylebook

"Use commas to separate elements in a series, but do not put a comma before the conjunction in a simple series. [...] 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. In the United States, the choice is between journalistic style (no serial comma) and "literary" style (with serial comma); consistent use of the serial comma is usually recommended for college writing."

Australian style guides opposing mandatory use

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. ... Generally, however, a comma is not used before and, or or etc. in a list."

Other languages

In the following languages, the serial comma is not the norm and may go against punctuation rules: