In general, the comma shows that the words immediately before the comma are less closely or exclusively linked
grammatically to those immediately after the comma than they might be otherwise. The comma performs a number of functions in
English writing. It is used in generally similar ways in other languages, particularly European ones, although the rules on comma usage – and their rigidity – vary from language to language.
List separator and the serial (Oxford) comma Commas are placed between items in lists, as in
They own a cat, a dog, two rabbits, and seven mice. Whether the final conjunction, most frequently
and, should be preceded by a comma, called the
serial comma, is one of the most disputed linguistic or stylistic questions in English: • They served apples, peaches, and bananas. (serial comma used) • They served apples, peaches and bananas. (serial comma omitted) The serial comma is used much more often, usually routinely, in the United States. A majority of American style guides mandate its use, including
The Chicago Manual of Style,
Strunk and
White's classic
The Elements of Style, and the
U.S. Government Publishing Office's
Style Manual. Conversely, the
AP Stylebook for journalistic writing advises against it. The serial comma is also known as the Oxford comma, Harvard comma, or series comma. Although less common in British English, its usage occurs within both American and British English. It is called the Oxford comma because of its long history of use by Oxford University Press. According to ''New Hart's Rules'', "house style will dictate" whether to use the serial comma. "The general rule is that one style or the other should be used consistently." No association with region or dialect is suggested, other than that its use has been strongly advocated by Oxford University Press. Its use is preferred by
Fowler's
Modern English Usage. It is recommended by the United States
Government Printing Office and
Harvard University Press. Use of a comma may prevent ambiguity: • The sentence
I spoke to the boys, Sam and Tom could mean either
I spoke to the boys and Sam and Tom (I spoke to more than three people) or
I spoke to the boys, who are Sam and Tom (I spoke to two people); •
I spoke to the boys, Sam, and Tom – must be
the boys and Sam and Tom (I spoke to more than three people). The serial comma does not eliminate all confusion. Consider the following sentence: •
I thank my mother, Anne Smith, and Thomas. This could mean either
my mother and Anne Smith and Thomas (three people) or
my mother, who is Anne Smith; and Thomas (two people). This sentence might be recast as "my mother (Anne Smith) and Thomas" for clarity. •
I thank my mother, Anne Smith and Thomas. Because the comma after "mother" is conventionally used to prepare the reader for an
appositive phrase – that is, a renaming of or further information about a noun – this construction formally suggests that my mother's name is "Anne Smith and Thomas". Because that is implausible, it is relatively clear that the construction refers to two separate people. Compare "I thank my friend, Smith and Wesson", in which the ambiguity is obvious to those who recognise
Smith and Wesson as a business name. As a
rule of thumb,
The Guardian Style Guide suggests that straightforward lists (
he ate ham, eggs and chips) do not need a comma before the final "and", but sometimes it can help the reader (
he ate cereal, kippers, bacon, eggs, toast and marmalade, and tea).
The Chicago Manual of Style and other academic writing guides require the serial comma: all lists must have a comma before the "and" prefacing the last item in a series . If the individual items of a list are long, complex, affixed with description, or themselves contain commas,
semicolons may be preferred as separators, and the list may be introduced with a
colon. In
news headlines, a comma might replace the word "and", even if there are only two items, in order to save space, as in this headline from
Reuters: •
Trump, Macron engage in a little handshake diplomacy. Separation of clauses Commas are often used to separate
clauses. In English, a comma is often used to separate a
dependent clause from the
independent clause if the dependent clause comes first:
After I fed the cat, I brushed my clothes. (Compare this with
I brushed my clothes after I fed the cat.) A
relative clause takes commas if it is non-
restrictive, as in
I cut down all the trees, which were over six feet tall. (Without the comma, this would mean that only the trees more than six feet tall were cut down.) Some style guides prescribe that two
independent clauses joined by a coordinating
conjunction (
for,
and,
nor,
but,
or,
yet,
so) must be separated by a comma placed before the conjunction. In the following sentences, where the second clause is independent (because it can stand alone as a sentence), the comma is considered by those guides to be necessary: •
Mary walked to the party, but she was unable to walk home. • ''Designer clothes are silly, and I can't afford them anyway.'' • ''Don't push that button, or twelve tons of high explosives will go off right under our feet!'' In the following sentences, where the second half of the sentence is a dependent clause (because it does not contain an explicit
subject), those guides prescribe that the comma be omitted: •
Mary walked to the party but was unable to walk home. • ''I think designer clothes are silly and can't afford them anyway.'' However, such guides permit the comma to be omitted if the second independent clause is very short, typically when the second independent clause is an
imperative, •
She had very little to live on, but would never have dreamed of taking what was not hers. In some languages, such as
German and
Polish, stricter rules apply on comma use between clauses, with dependent clauses always being set off with commas, and commas being generally proscribed before certain coordinating conjunctions. The joining of two independent sentences with a comma and no conjunction (as in
"It is nearly half past five, we cannot reach town before dark.") is known as a
comma splice and is sometimes considered an error in English; in most cases a semicolon should be used instead. A comma splice should not be confused, though, with the literary device called
asyndeton, in which coordinating conjunctions are purposely omitted for a specific stylistic effect. A much debated comma is the one in the
Second Amendment to the United States Constitution, which says
"A well regulated Militia being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed." but ratified by several states as
"A well regulated Militia being necessary to the security of a free State, the right of the people to keep and bear Arms shall not be infringed." which has caused much debate on its interpretation.
Certain adverbs Commas are always used to set off certain
adverbs at the beginning of a sentence, including
however,
in fact,
therefore,
nevertheless,
moreover,
furthermore, and
still. •
Therefore, a comma would be appropriate in this sentence. •
Nevertheless, I will not use one. If these adverbs appear in the middle of a sentence, they are followed and preceded by a comma. As in the second of the two examples below, if a semicolon separates the two sentences and the second sentence starts with an adverb, this adverb is preceded by a semicolon and followed by a comma. •
In this sentence, furthermore, commas would also be called for. •
This sentence is a bit different; however, a comma is necessary as well. Using commas to offset certain adverbs is optional, including
then,
so,
yet,
instead, and
too (meaning
also). • ''So, that's it for this rule.'' or • ''So that's it for this rule.'' •
A comma would be appropriate in this sentence, too. or •
A comma would be appropriate in this sentence too. Parenthetical phrases Commas are often used to enclose
parenthetical words and phrases within a sentence (i.e., information that is not essential to the meaning of the sentence). Such phrases are both preceded and followed by a comma, unless that would result in a doubling of punctuation marks or the parenthetical is at the start or end of the sentence. The following are examples of types of parenthetical phrases: • Introductory phrase:
Once upon a time, my father ate a muffin. • Interjection:
My father ate the muffin, gosh darn it! • Aside: ''My father, if you don't mind me telling you this, ate the muffin.'' •
Appositive:
My father, a jaded and bitter man, ate the muffin. • Absolute phrase:
My father, his eyes flashing with rage, ate the muffin. • Free modifier:
My father, chewing with unbridled fury, ate the muffin. • Resumptive modifier:
My father ate the muffin, a muffin which no man had yet chewed. • Summative modifier:
My father ate the muffin, a feat which no man had attempted. The parenthesization of phrases may change the connotation, reducing or eliminating
ambiguity. In the following example, the thing in the first sentence that is relaxing is the cool day, whereas in the second sentence, it is the walk since the introduction of commas makes "on a cool day" parenthetical: :
They took a walk on a cool day that was relaxing. :
They took a walk, on a cool day, that was relaxing. As more phrases are introduced, ambiguity accumulates, but when commas separate each phrase, the phrases clearly become modifiers of just one thing. In the second sentence below, that thing is
the walk: :
They took a walk in the park on a cool day that was relaxing. :
They took a walk, in the park, on a cool day, that was relaxing. Between adjectives A comma is used to separate
coordinate adjectives (i.e.,
adjectives that directly and equally modify the following noun). Adjectives are considered coordinate if the meaning would be the same if their order were reversed or if
and were placed between them. For example: •
The dull, incessant droning but
the cute little cottage. •
The devious lazy red frog suggests there are lazy red frogs (one of which is devious), while
the devious, lazy red frog does not carry this connotation.
Before quotations Some writers precede quoted material that is the grammatical object of an active verb of speaking or writing with a comma, as in, "Mr. Kershner says, 'You should know how to use a comma. Quotations that follow and support an assertion are often preceded by a
colon rather than a comma. Other writers do not put a comma before quotations unless one would occur anyway. Thus, they would write "Mr. Kershner says 'You should know how to use a comma.
In dates Month day, year When a date is written as a month followed by a day followed by a year, a comma separates the day from the year: December 19, 1941. This style is common in American English. The comma is used to avoid confusing consecutive numbers: December 19 1941. Most style manuals, including
The Chicago Manual of Style and the
AP Stylebook, also recommend that the year be treated as a parenthetical, requiring a second comma after it:
"Feb. 14, 1987, was the target date." If just the month and year are given, no commas are used: "Her daughter may return in June 2009 for the reunion."
Day month year When the day precedes the month, the month name separates the numeric day and year, so commas are not necessary to separate them: "The
Raid on Alexandria was carried out on 19 December 1941."
In geographical names Commas are used to separate parts of geographical references, such as city and state (
Dallas, Texas) or city and country (
Kampala, Uganda). Additionally, most style manuals, including
The Chicago Manual of Style and the
AP Stylebook, recommend that the second element be treated as a parenthetical, requiring a second comma after:
"The plane landed in Kampala, Uganda, that evening." The
United States Postal Service and
Royal Mail recommend leaving out punctuation when writing addresses on actual letters and packages, as the marks hinder
optical character recognition.
Canada Post has similar guidelines, making only very limited use of hyphens.
In mathematics Similar to the case in natural languages, commas are often used to delineate the boundary between multiple
mathematical objects in a list (e.g., (3, 5, 12)). Commas are also used to indicate the
comma derivative of a
tensor.
In numbers In representing large numbers, from the right side to the left, English texts usually use commas to separate each group of three digits in front of the decimal. This is almost always done for numbers of six or more digits, and often for four or five digits but not in front of the number itself. However, in much of Europe, Southern Africa and Latin America,
periods or spaces are used instead; the comma is used as a
decimal separator, equivalent to the use in English of the
decimal point. In India, the groups are two digits, except for the rightmost group, which is of three digits. In some styles, the comma may not be used for this purpose at all (e.g. in the
SI writing style); a space may be used to separate groups of three digits instead.
In names Commas are used when rewriting names in
lexical name order to present the surname first, generally in instances of alphabetization by surname:
Smith, John. They are also used before many titles that follow a name:
John Smith, Ph.D. It can also be used in regnal names followed by their occupation:
Louis XIII, king of France and Navarre. Similarly in lists that are presented with an inversion:
socks, green: 3 pairs; socks, red: 2 pairs; tie, regimental: 1.
Ellipsis Commas may be used to indicate that a word, or a group of words, has been omitted, as in
The cat was white; the dog, brown. (Here the comma replaces
was.)
Vocative Commas are placed before, after, or around a noun or pronoun used independently in speaking to some person, place, or thing: •
I hope, John, that you will read this. Between the subject and predicate In his 1785 essay
An Essay on Punctuation,
Joseph Robertson advocated a comma between the subject and predicate of long sentences for clarity; however, this usage is regarded as an error in modern times. •
The good taste of the present age, has not allowed us to neglect the cultivation of the English language. •
Whoever is capable of forgetting a benefit, is an enemy to society. Differences between American and British usage in placement of commas and quotation marks The comma and the
quotation mark can be paired in several ways. In Great Britain and many other parts of the world, punctuation is usually placed within quotation marks only if it is part of what is being quoted or referred to: • My mother gave me the nickname "Bobby Bobby Bob Bob Boy", which really made me angry. In American English, the comma was commonly included inside a quotation mark: ==Languages other than English==