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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. Other fonts give it the appearance of a miniature filled-in figure on the baseline. The comma is used in many contexts and
languages A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign language) and writing. Most languages have a writing system composed of glyphs to inscribe the original soun ...
, mainly to separate parts of a sentence such as
clause In language, a clause is a part of the sentence that constitutes or comprises a predicate (grammar), predicate. A typical clause consists of a subject (grammar), subject and a predicate, the latter typically a verb phrase, a verb with any object ...
s and items in lists, mainly when there are three or more items listed. The word ''comma'' comes from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of 2018; Athens is ...
(), which originally meant a cut-off piece, specifically in
grammar In linguistics, the grammar (from Ancient Greek ''grammatikḗ'') of a natural language is its set of structure, structural constraints on speakers' or writers' composition of clause (linguistics), clauses, phrases, and words. The term can also ...
, a short
clause In language, a clause is a part of the sentence that constitutes or comprises a predicate (grammar), predicate. A typical clause consists of a subject (grammar), subject and a predicate, the latter typically a verb phrase, a verb with any object ...
. A comma-shaped mark is used as a
diacritic A diacritic (also diacritical mark, diacritical point, diacritical sign, or accent) is a glyph added to a letter or basic glyph. The term derives from the Ancient Greek Ancient Greek includes the forms of the Greek language used in anc ...
in several writing systems and is considered distinct from the cedilla. In
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages () ...
, the rough and smooth breathings () appear above the letter. In Latvian, Romanian, and Livonian, the comma diacritic appears below the letter, as in . ''For the notation'' ''and'' /x/ ''used in this article, see grapheme and phoneme respectively.''

# History

The development of punctuation is much more recent than the alphabet. In the 3rd century BC, Aristophanes of Byzantium invented a system of single Interpunct, dots () at varying levels, which separated verses and indicated the amount of breath needed to complete each fragment of the text when Reading (process), reading aloud. The different lengths were signified by a dot at the bottom, middle, or top of the line. For a short passage, a in the form of a 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 , a diagonal slash (punctuation), slash known as , 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 the words, the phrases, and the 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', etc.

# Uses in English

In general, the comma shows that the words immediately before the comma are less closely or exclusively linked grammar, grammatically to those immediately after the comma than they might be otherwise. The comma performs a number of functions in English language, 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.

## Separation of clauses

Commas are often used to separate
clause In language, a clause is a part of the sentence that constitutes or comprises a predicate (grammar), predicate. A typical clause consists of a subject (grammar), subject and a predicate, the latter typically a verb phrase, a verb with any object ...
s. 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-restrictiveness, 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 Grammatical conjunction, 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 not an independent clause (because it does not contain an explicit subject (grammar), 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 mood, imperative, 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: * ''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 language, German and Polish language, 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''. * ''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.''

## Parenthetical phrases

Commas are often used to enclose parenthesis (rhetoric), 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.'' *Apposition, 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., adjective#Adjective order, 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 (punctuation), 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 month and year are given, no commas are used: "Her daughter April 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 (1941), 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.

## 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., $\left(3, 5, 12\right)$). 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, full stop, periods or spaces are used instead; the comma is used as a decimal separator, equivalent to the use in English of the decimal separator, 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 International System of Units#Writing unit symbols and the values of quantities, SI writing style); a space may be used to separate groups of three digits instead.

## In names

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''.

## 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 (clergyman), 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 is commonly included inside a quotation mark: *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.

# Languages other than English

## Western European languages

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.

## Comma variants

The basic comma is defined in Unicode as , 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
diacritic A diacritic (also diacritical mark, diacritical point, diacritical sign, or accent) is a glyph added to a letter or basic glyph. The term derives from the Ancient Greek Ancient Greek includes the forms of the Greek language used in anc ...
s 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..

## Languages other than Western European

Korean punctuation uses both commas and interpuncts for lists. In Unicode 5.2.0 "numbers with commas" ( through ) were added to the Enclosed Alphanumeric Supplement block for compatibility with the ARIB STD B24 character set. Hebrew script is also written from right to left. However, Hebrew punctuation includes only a regular comma (). Dravidian languages such as Tamil language, Tamil, Telugu language, Telugu, Kannada, and Malayalam also use the punctuation mark in similar usage to that of European languages with similar spacing.:ta:கால்புள்ளி (தமிழ் நடை)

# Computing

In the common character (computing), character encoding systems Unicode and ASCII, character 44 (hexadecimal, 0x2C) corresponds to the comma symbol. The HTML numeric character reference is `&#44;`. In many computer languages commas are used as a field delimiter to separate arguments to a Subroutine, function, to separate elements in a Array data type, list, and to perform data designation on multiple variables at once. In the C (programming language), C programming language the comma symbol is an Comma operator, operator which evaluates its first Parameter (computer programming), argument (which may have side-effects) and then returns the value of its evaluated second argument. This is useful in ''for'' statement (programming), statements and Macro (computer science), macros. In Smalltalk and APL (programming language), APL, the comma operator is used to Concatenation, concatenate collections, including strings. In APL, it is also used Monad (functional programming), monadically to rearrange the items of an array into a list. In Prolog, the comma is used to denote Logical Conjunction ("and"). The comma-separated values (CSV) format is very commonly used in exchanging text data between database and spreadsheet formats.

# Diacritical usage

In French language, French, a (not a comma) is used beneath a , producing , to indicate that the is pronounced like (a 'soft c') and not like (a 'hard c'): , , . Depending on the knowledge and resources of the typist or typesetter, the is irregularly conserved on French words used in English, like façade. The comma is used as a
diacritic A diacritic (also diacritical mark, diacritical point, diacritical sign, or accent) is a glyph added to a letter or basic glyph. The term derives from the Ancient Greek Ancient Greek includes the forms of the Greek language used in anc ...
mark in Romanian language, Romanian under (, ), and under (, ). A cedilla is occasionally used instead of it, but this is technically incorrect. The symbol ('D-comma, d with comma below') was used as part of the Romanian alphabet, Romanian transitional alphabet (19th century) to indicate the sounds denoted by the Latin letter or letters , where derived from a Dze, Cyrillic ѕ (, ). The comma and the cedilla are both derivative of (a small cursive ) placed below the letter. From this standpoint alone, , , and could potentially be regarded as stand-ins for /sz/, /tz/, and /dz/ respectively. In Latvian language, Latvian, the comma is used on the letters , , , , and historically also , to indicate Palatalization (phonetics), palatalization. Because the lowercase letter has a descender, the comma is rotated 180° and placed over the letter. Although their Adobe Systems, Adobe glyph names are 'letter with comma', their names in the Unicode Standard are 'letter with a cedilla'. They were introduced to the Unicode standard before 1992 and, per Unicode Consortium policy, their names cannot be altered. In Livonian language, Livonian, whose alphabet is based on a mixture of Latvian and Estonian language, 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 consonant, palatal plosive consonant, plosive phonemes which Latvian writes as and respectively. In Czech language, Czech and Slovak language, 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 (typography), ascender. Other ascender letters with carons, such as letters (used in Finnish Kalo language, Finnish Romani and Lakota language, Lakota) and (used in Skolt Sami language, Skolt Sami), did not modify their carons to superscript commas. In 16th-century Guatemala, the archaic letter cuatrillo with a comma ( and ) was used to write Mayan languages.

* Hebrew cantillation

## General

*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

## Related history

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

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