The comma ( , ) is a punctuation mark that appears in several variants in different languages. It has the same shape as an apostrophe ( ' ) or single closing quotation mark in many typefaces, but it differs from them in being placed on the baseline of the text. Some typefaces render it as a small line, slightly curved or straight but inclined from the vertical, or with the appearance of a small, filled-in figure 9.
The comma is used in many contexts and languages, mainly to separate parts of a sentence such as clauses, and items in lists, particularly when there are three or more items listed. The word comma comes from the Greek (kómma), which originally meant a cut-off piece; specifically, in grammar, a short clause.
A comma-shaped mark is used as a diacritic in several writing systems, and is considered distinct from the cedilla. The rough and smooth breathings (?, ?) appear above the letter in Ancient Greek, and the comma diacritic appears below the letter in Latvian, Romanian, and Livonian.
Punctuation is much more recent than the alphabet. In the 3rd century BC, Aristophanes of Byzantium invented a system of single dots (distinctiones) that separated verses (colometry) and indicated the amount of breath needed to complete each fragment of the text when reading aloud. The different lengths were signified by a dot at the bottom, middle, or top of the line. For a short passage (a komma), a media distinctio dot was placed mid-level ( · ). This is the origin of the concept of a comma, although the name came to be used for the mark itself instead of the clause it separated.
The mark used today is descended from a diagonal slash, or virgula suspensiva ( / ), used from the 13th to 17th centuries to represent a pause. The modern comma was first used by Aldus Manutius.
Moreover, the mark is used to separate words, phrases and clauses in a sentence to help it to be understood: to divide a sentence into easily assimilated bite-sized pieces. However, there are many other functions of the comma, such as "setting of questions", "emphasizing point of view", and etc.
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.
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.
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. The AP Stylebook for journalistic writing advises against it.
The serial comma is also known as the Oxford comma, Harvard comma, or series comma. It is sometimes perceived as overly careful or an Americanism, but 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.
It is used less often in British English, but some British style guides require it, including the Oxford University Press style manual and Fowler's Modern English Usage. Some writers of British English use it only where necessary to avoid ambiguity.
According to New Hart's Rules, "house style will dictate" whether to use the serial comma, and "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.
is more frequent in the United States than in England; in England it may be called an Oxford comma, because the Oxford University Press, uniquely in England, recommends it. 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 serial comma does not eliminate all confusion. Consider the following sentence:
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.
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. 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:
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:
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; 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.
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 the two sentences are separated by a semicolon and the second sentence starts with an adverb, this adverb is preceded by a semicolon and followed by a comma.
Using commas to offset certain adverbs is optional, including then, so, yet, instead, and too (meaning also).
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:
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:
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 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 month and year are given, no commas are used: "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 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."
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 five or four 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. 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.
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, 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:
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.
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.
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 , COMMA (HTML
,), and many variants by typography or language are also defined.
|Character||Unicode point||Unicode name||Notes|
|,||U+002C||COMMA||Prose in European languages|
Decimal separator in Continental Europe, Brazil, and some other Latin American countries
|?||U+02BB||MODIFIER LETTER TURNED COMMA||Used as ?okina in Hawaiian|
|?||U+060C||ARABIC COMMA||Used in all languages using Arabic alphabet|
Also used in other languages, including Syriac and Thaana
|?||U+2E32||TURNED COMMA||Palaeotype transliteration symbol; indicates nasalization|
|?||U+2E41||REVERSED COMMA||Used in Sindhi, among others|
|?||U+2E49||DOUBLE STACKED COMMA||Used in the Eastern Orthodox liturgical book Typikon|
|?||U+3001||IDEOGRAPHIC COMMA||Used in Chinese and Japanese writing systems|
|?||U+FE10||PRESENTATION FORM FOR VERTICAL COMMA||Used in vertical writing|
|?||U+FE11||PRESENTATION FORM FOR VERTICAL IDEOGRAPHIC COMMA||Used in vertical writing|
|?||U+FE51||SMALL IDEOGRAPHIC COMMA|
|?||U+FF64||HALFWIDTH IDEOGRAPHIC COMMA|
Some languages use a completely different sort of character for the purpose of the comma.
|Character||Unicode point||Unicode name||Notes|
|·||U+00B7||MIDDLE DOT||Used as a comma in Georgian|
|?||U+2218||RING OPERATOR||Used as a comma in Malayalam|
|?||U+1808||MONGOLIAN MANCHU COMMA|
|?||U+A4FE||LISU PUNCTUATION 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).
|Character||Unicode point||Unicode name||Notes|
|?||U+02BD||MODIFIER LETTER REVERSED COMMA||Indicates weak aspiration|
|U+0312||COMBINING TURNED COMMA ABOVE||Latvian diacritic cedilla above|
|U+0313||COMBINING COMMA ABOVE||Greek psili, smooth breathing mark|
|U+0314||COMBINING REVERSED COMMA ABOVE||Greek dasia, rough breathing mark|
|U+0315||COMBINING COMMA ABOVE RIGHT|
|U+0326||COMBINING COMMA BELOW||Diacritical mark in Romanian, Latvian, Livonian|
|,||U+201A||SINGLE LOW-9 QUOTATION MARK||Opening single quotation mark in some languages|
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 () and it is officially romanized as a Latin comma, 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 ?, (ó,ti, "whatever") from (óti, "that").
The enumeration or ideographic comma-- 、 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 , s , p dùnhào) is usually used only to separate items in lists, while in Japan it is the more common form of comma (, r t?ten, lit. "clause mark"). In documents that mix Japanese and Latin scripts, the full-width comma ( ， FULLWIDTH COMMA) is used; this is the standard form of comma (t , s , 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.
The comma in the Arabic script (used by Arabic, Urdu, and Persian, etc.) is inverted, upside-down: '?' ( ، ARABIC COMMA), in order to distinguish it from the Arabic diacritic ?ammah (?), representing the vowel /u/, which is similarly comma-shaped. In Arabic texts, Western-styled comma (?) is used as a decimal point.
Reversed comma ( ⹁ REVERSED COMMA) is used in Sindhi when written in Arabic script. It is different from the standard Arabic comma.
In the C programming language the comma symbol is an operator which evaluates its first argument (which may have side-effects) and then returns the value of its evaluated second argument. This is useful in for statements and macros.
The comma-separated values (CSV) format is very commonly used in exchanging text data between database and spreadsheet formats.
In French, a comma is used beneath a c, producing ç, to indicate that the c is pronounced like s (a "soft c") and not like k (a "hard c"): français, garçon. Depending on the knowledge and resources of the typist or typesetter, the ç is irregularly conserved on French words used in Engljsh, like façade.
The comma is used as a diacritic mark in Romanian under the s (?, ?), and under the t (?, ?). A cedilla is occasionally used instead of it, but this is technically incorrect. The symbol d? (d with comma below) was used as part of the Romanian transitional alphabet (19th century) to indicate the sounds denoted by the Latin letter z or letters dz, where derived from a Cyrillic ? (/dz/). The comma and the cedilla are both derivative of a small cursive z (?) placed below the letter. From this standpoint alone, ?, ?, and d? could potentially be regarded as stand-ins for sz, tz, and dz respectively.
In Latvian, the comma is used on the letters ?, ?, ?, ?, and historically also ?, to indicate palatalization. Because the lowercase letter g has a descender, the comma is rotated 180° and placed over the letter. Although their Adobe glyph names are commas, their names in the Unicode Standard are g, k, l, n, and r with a cedilla. They were introduced to the Unicode standard before 1992, and their name cannot be altered.
In Livonian, whose alphabet is based on a mixture of Latvian and Estonian alphabets, the comma is used on the letters ?, ?, ?, ?, ? to indicate palatalization in the same fashion as Latvian, except that Livonian uses ? and ? represent the same palatal plosive phonemes which Latvian writes as ? and ? respectively.
In Czech and Slovak, the diacritic in the characters ?, ?, and ? resembles a superscript comma, but it is used instead of a caron because the letter has an ascender. Other ascender letters with carons, such as letters ? (used in Finnish Romani and Lakota) and ? (used in Skolt Sami), did not modify their carons to superscript commas.
Do not join independent clauses by a comma.
When a phrase refers to a month, day and year, set off the year with commas... Feb. 14, 1987, was the target date.
A comma is sometimes used to indicate the omission of one or more words.
In the British style (OUP 1983), all signs of punctuation used with words and quotation marks must be placed according to the sense.
The comma used in Arabic script is not only a mirror image of its Latin counterpart, but its tail is also turned upwards in order to avoid any possibility of confusing it with the Dammah, the u short vowel mark.