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The comma ( , ) is a punctuation mark, and it appears in several variants in various 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 number 9. It is used to separate parts of a sentence such as clauses and lists of three or more things.
The comma is used in many contexts and languages, mainly for separating things. According to the Oxford English Dictionary, the word comma comes directly from the Greek komma (κόμμα), which means something cut off or a short clause. A comma can also be used as a diacritic when combined with other characters.
The basic comma is defined in Unicode as U+002C , comma (HTML:
,) but 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 other Latin American countries.|
|ʻ||U+02BB||MODIFIER LETTER TURNED COMMA||used as ʻOkina|
|ʽ||U+02BD||MODIFIER LETTER REVERSED COMMA||Indicates weak aspiration|
|،||U+060C||ARABIC COMMA||Also used in other languages|
|、||U+3001||IDEOGRAPHIC COMMA||Used in Japanese and Chinese languages|
|︐||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|
|̒||U+0312||COMBINING TURNED COMMA ABOVE||Latvian diacrtic 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||Romanian, Latvian, Livonian|
|꓾||U+A4FE||LISU PUNCTUATION COMMA|
|᠈||U+1808||MONGOLIAN MANCHU COMMA|
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 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.
In general, the comma is used where ambiguity might otherwise arise, to indicate an interpretation of the text such that the words immediately before and after the comma are less closely or exclusively linked in the associated grammatical structure than they might be otherwise. The comma may be used to perform 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 used to join items in lists, as in They own a cat, a dog, two rabbits, and six mice. In English, a comma needs to be before the final conjunction (and, or, nor) in a list of more than two elements. A comma used in such a position is called a serial comma or an Oxford or Harvard comma (after the Oxford University Press and Harvard University Press, both prominent advocates of this style). In some cases, use or omission of such a comma may serve to avoid ambiguity:
Use of serial comma disambiguating:
Omission of serial comma disambiguating:
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 those trees over 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 (it cannot stand alone), those guides prescribe that the comma be omitted (Note that it is dependent upon the subject's presence in the sentence's second phrase):
However, the comma may be omitted if the second independent clause is very short, typically when the second independent clause is an imperative. In the following sentence, it is sometimes considered acceptable to omit the comma, even though the second clause is independent:
Long coordinating clauses are usually separated by commas:
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 often 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 below examples, if the two sentences are separated by a semicolon and the second sentence starts with an adverb, then it 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; that is, 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:
A comma is used to set off quoted material that is the grammatical object of an active verb of speaking or writing, as in Mr. Kershner says, "You should know how to use a comma." Quotations that follow and support an assertion should be set off by a colon rather than 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 necessary because of the otherwise confusing consecutive numbers, compare December 19 1941. Additionally, most style manuals, including The Chicago Manual of Style and the AP Stylebook, recommend that the year be treated as a parenthetical, requiring a second comma after it: "Feb. 14, 1987, was the target date." However, one exception to this general rule is that you do not include a comma after the year where the date is serving as a specifically identifying adjective - almost as a title: "The September 11, 2001 attacks on the WTC brought a renewed feeling of patriotism."
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, English texts usually use commas to separate each group of three digits. This is almost always done for numbers of six or more digits, and often for five or four digits. 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 addition, the comma may not be used for this purpose at all in some number systems, e.g. the SI writing style; a space may be used to separate groups of three digits instead.
Commas are used when writing names that are presented 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.
Commas may be used to indicate that a word 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:
The comma and the quotation mark pairing can be used in several ways. In American English, the comma is commonly included inside a quotation, regardless of whether the comma is part of the original quotation. For example:
However, in British English, punctuation is placed within quotation marks only if it is part of what is being quoted or referred to. Thus:
The use of the serial comma is sometimes perceived as an Americanism, but common practice varies in both American and British English. Barbara Child claims that in American English there is a trend toward a decreased use of the comma (Child, 1992, p. 398). This is reinforced by an article by Robert J. Samuelson in Newsweek. Lynne Truss says that this is equally true in the UK, where it has been a slow, steady trend for at least a century:
Nowadays… A passage peppered with commas—which in the past would have indicated painstaking and authoritative editorial attention—smacks simply of no backbone. People who put in all the commas betray themselves as moral weaklings with empty lives and out-of-date reference books. (Truss, 2004, p. 97–98)
Use of a comma after the last of a series is also being discontinued, especially in the U.S., even though this may lead to some confusion, as in the quotation: "I thank my parents, the Pope and Sinéad O'Connor".
In his 1963 book "Of Spies and Stratagems", Stanley P. Lovell recalls that, 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.
Punctuation has been added to many languages which originally developed without it, including a number of different comma forms.
European languages like German, French, Italian, Spanish, and Portuguese use the same comma as English with similar spacing.
Japanese punctuation commonly uses the '、' (tōten, 読点, U+3001 IDEOGRAPHIC COMMA) in native text and full-width comma '，' (U+FF0C FULLWIDTH COMMA) when mixing Japanese and Latin alphabet characters.
Languages such as Tamil and its major branch-languages (Telugu, Kannada and Malayalam)also use the punctuation mark in similar usage to that of European Languages with similar spacing.
Chinese punctuation normally uses '，' (U+FF0C FULLWIDTH COMMA) but has the "enumeration comma" '、' (simplified Chinese: 顿号; traditional Chinese: 頓號; pinyin: dùnhào; literally "pause mark", U+3001 IDEOGRAPHIC COMMA) for lists. The comma is used to join together clauses that deal with a certain topic or line of thinking. As such, what would appear to an English speaker to be a comma splice is very commonly seen in Chinese writing. Often, the entirety of a long paragraph can consist of clauses joined by commas, with the sole period coming only at the end. Unlike in English, a comma is allowed between a subject and its predicate.
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.
The comma is used as a diacritic mark in Romanian under the s (Ș, ș), and under the t (Ț, ț). A cedilla is occasionally used instead of it (notably in the Unicode glyph names), but this is technically incorrect. The symbol d̦ (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 ѕ (/dz/). The comma and the cedilla are both derivative of a small cursive z (ʒ) placed below the letter. From this standpoint alone, ș, ț, and d̦ could potentially be regarded as stand-ins for sz, tz, and dz respectively.
In Latvian, the comma is used on the letters ģ, ķ, ļ, ņ, and historically also ŗ, 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. For input Ģ use Alt 290 and Alt 291 sequences, for Ķ use Alt 310 and Alt 311, for Ļ use Alt 315 and Alt 316, for Ņ use Alt 325 and Alt 326.
In the Czech and Slovak languages, the diacritics in the characters ď, ť, and ľ resemble superscript commas, but they are modified carons because they have ascenders. Other ascender letters with carons, such as letters ȟ (used in Finnish Romani and Lakota) and ǩ (used in Skolt Sami), did not modify their carons to superscript commas.