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)
• We cleaned up cores, pits and skins. (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 Printing Office 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.[7]

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.[8] Its use is preferred by Fowler's Modern English Usage. It is recommended by the United States Government Printing Office, Harvard University Press, and the classic Elements of Style of Strunk and White.

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 apposite phrase – that is, a renaming of or further information about a noun – this construction suggests that my mother's name is "Anne Smith and Thomas". 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[9] 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 (see Differences between American and British usage below).

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:[10]

• Trump, Macron engage in a little handshake diplomacy.

Commas are often used to separate clauses. In English, a comma is 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.[11][12] 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 not an independent 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,[11][12] as in:

• Sit down and shut up.

The above guidance is not universally accepted or applied. Long coordinate clauses are nonetheless usually separated by commas:[13]

• She had very little to live on, but she would never have dreamed of taking what was not hers.

In some languages, such as German and Polish, stricter rules apply on comma usage 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;[14] in most cases a semicolon should be used instead. A comma splice should not be confused, though, with asyndeton, a literary device used for a specific effect in which coordinating conjunctions are purposely omitted.

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 similar; however, a semicolon 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.

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.[15]
• 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.

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.

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."

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[16] and the AP Stylebook,[17] 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 month and year are given, no commas are used:[18] "Her daughter April may return in June 2009 for the reunion."

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."

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[19] and the AP Stylebook,[20] recommend that the second element be treated as a parenthetical, requiring a second comma after: "The plane landed in Kampala, Uganda, that evening."[21]

The United States Postal Service[22] and Royal Mail[23] recommend leaving out punctuation when writing addresses on actual letters and packages, as the marks hinder optical character recognition.

Similar to the case in natural languages, commas are often used to delineate the boundary between multiple mathematical objects in a list (e.g., ${\displaystyle (3,5,12)}$).[24] Commas are also used to indicate the comma derivative of a tensor.[25]

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.[26] 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.[27] In India, the groups are two digits, except for the rightmost group. In some styles, the comma may not be used for this purpose at all (e.g. in the SI writing style[28]); a space may be used to separate groups of three digits instead.

Commas are used when rewriting names 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.

Similarly in lists that are presented with an inversion: ...; socks, green: 3 pairs; socks, red: 2 pairs; tie, regimental: 1.

Commas may be used to indicate that a word, or a group of words, has been omitted,[29] as in The cat was white; the dog, brown. (Here the comma replaces was.)

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.

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.

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:[30][31][32]

• My mother gave me the nickname "Bobby Bobby Bob Bob Boy", which really made me angry.

In American English, the comma is commonly included inside a quotation mark:[30][31]

• My mother gave me the nickname "Bobby Bobby Bob Bob Boy," which really made me angry.

During the Second World War, the British carried the comma over into abbreviations. Specifically, "Special Operations, Executive" was written "S.O.,E.". Nowadays, even the full stops are frequently discarded.[33]

Western European languages like German, French, Italian, Spanish, and Portuguese use the same comma as English with similar spacing, though usage may be somewhat different. For instance, in Standard German, subordinate clauses are always preceded by commas.

The basic comma is defined in Unicode as U+002C , COMMA (HTML , · ,), and many variants by typography or language are also defined.

Some languages use a completely different sort of character for the purpose of the comma.

There are also a number of comma-like diacritics with "COMMA" in their Unicode names. These do not serve a punctuation function. A comma-like low quotation mark is also available (shown below; raised single quotation marks are not shown).

Various other Unicode characters combine commas or comma-like figures with other characters, and are not shown here..

Modern Greek uses the same Unicode comma for its kómma (κόμμα)[34] and it is officially romanized as a Latin comma,[35] but it has additional roles owing to its conflation with the former hypodiastole, a curved interpunct used to disambiguate certain homonyms. The comma therefore functions as a silent letter in a handful of Greek words, principally distinguishing ό,τι (ó,ti, "whatever") from ότι (óti, "that").[34]

The enumeration or ideographic comma — U+3001 、 IDEOGRAPHIC COMMA — is used in Chinese, Japanese punctuation, and somewhat in Korean punctuation. In the People's Republic of China and in North/South Korea, this comma (t 頓號, s 顿号, p dùnhào) is usually used only to separate items in lists, while in Japan it is the more common form of comma (読点, r tōten, lit. "clause mark"). In documents that mix Japanese and Latin scripts, the full-width comma (U+FF0C ， FULLWIDTH COMMA) is used; this is the standard form of comma (t 逗號, s 逗号, p dòuhào) in China. Since East Asian typography permits commas to join clauses dealing with certain topics or lines of thought, commas may separate subjects and predicates and constructions that would be considered a "comma splice" in English are acceptable and commonly encountered.

Korean punctuation uses both commas and interpuncts for lists.

In Unicode 5.2.0 "numbers with commas" (U+1F101 🄁 through U+1F10A 🄊 ) were added to the Enclosed Alphanumeric Supplement block for compatibility with the ARIB STD B24 character set.[36][37]

The comma in the Arabic script (used by Arabic, Urdu, and Persian, etc.) is inverted, upside-down: ⟨،⟩ (U+060C ، ARABIC COMMA), in order to distinguish it from the Arabic diacritic ḍammah ⟨ُ⟩, representing the vowel /u/, which is similarly comma-shaped.[38] In Arabic texts, Western-styled comma (٫) is used as a decimal point.

Reversed comma (U+2E41 ⹁ REVERSED COMMA) is used in Sindhi when written in Arabic script. It is different from the standard Arabic comma.

Hebrew script is also written from right to left. However, Hebrew punctuation includes only a regular comma (,).

Dravidian languages such as Tamil, Telugu, Kannada, and Malayalam also use the punctuation mark in similar usage to that of European languages with similar spacing.[39]

• Comma splice
• Copy editing
• Decimal separator
• English punctuation
• Latin-script alphabet
• List of typographical symbols and punctuation marks
• Ogonek
• Part of speech
• Sentence clause structure
• Traditional grammar

• Global spread of the printing press
• History of printing in East Asia
• History of sentence spacing
• History of Western typography