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 κόμμα (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 (ἁ, ἀ) appear above the letter in Ancient Greek, and the comma diacritic appears below the letter in Latvian, Romanian, and Livonian.
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.
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.Eats%2C%20Shoot%20%26%20Leaves%3A%20The%20Zer]] The different lengths were signified by a dot at the bottom, middle, or top of the line. For a short passage (a ), 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 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.
Uses in English
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. Some English style guides recommend that a comma be used before the final conjunction (and, or, nor) in a list of more than two elements. A comma used in such a position is variously called a serial comma, an Oxford comma, or a Harvard comma (after the Oxford University Press and Harvard University Press, both prominent advocates of this style). Such use of a comma sometimes prevents 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.
- 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.
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. (see Differences between American and British usage below)
- 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. 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.
- Sit down and shut up.
The above guidance is not universally accepted or applied.
- 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; 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.
- 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.
- 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.
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.
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: 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.
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:
- 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.
- My mother gave me the nickname "Bobby Bobby Bob Bob Boy," which really made me angry.
- My mother gave me the nickname "Bobby Bobby Bob Bob Boy", which really made me angry.
There is also some difference regarding the use of the serial comma, which is an optional comma placed before the coordinating conjunction in a list of three or more items:
- They served apples, peaches, and bananas.
- We cleaned up cores, pits and skins.
The serial comma is also known as the Oxford comma, Harvard comma, or series comma.
Opinions among writers and editors differ on whether to use the serial comma.
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.
Barbara Child advises that "it is a good idea to put a comma before the last item in a series", but claims that in the United States there is a trend toward a decreased use of the comma generally. Robert J. Samuelson]] in Lynne Truss says that general decline in usage of commas is equally true in the UK, where it has been a slow, steady trend for at least a century:
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.
In other languages
Punctuation has been added to many languages which originally developed without it, including a number of different comma forms.
Modern Greek uses the same Unicode comma for its kómma (κόμμα) 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 ό,τι (ó,ti, "whatever") from ότι (óti, "that").
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.
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. 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.
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, but this is technically incorrect. The symbol d̦ (d with comma below dz 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.
In Livonian, whose alphabet is based on a mixture of Latvian and Estonian alphabets, the comma is used on the letters ḑ, ļ, ņ, ŗ, ț to indicate palatalization in the same fashion as Latvian, except that Livonian uses ḑ and ț represent the same palatal plosive phonemes which Latvian writes as ģ and ķ respectively.
In Czech and Slovak, the diacritic in the characters ď, ť, and ľ 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 ȟ (used in Finnish Romani and Lakota) and ǩ* (used in Skolt Sami), did not modify their carons to superscript commas.
- List of typographical symbols
- Copy editing
- Decimal mark
- Latin-derived alphabet
- Parts of speech
- Punctuation of English
- Sentence clause structure
- Traditional grammar