Comma (punctuation)

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Punctuation marks
apostrophe ( ' ) ( ’ ) brackets ( ( ) ) ( [ ] ) ( { } ) ( 〈〉 ) colon ( : ) comma ( , ) dashes ( ‒ ) ( – ) ( — ) ( ― ) ellipsis ( … ) ( ... ) exclamation mark ( ! ) full stop/period ( . ) hyphen ( - ) ( ‐ ) interpunct ( · ) question mark ( ? ) quotation marks ( " ) ( ‘ ’ ) ( “ ” ) semicolon ( ; ) slash/solidus ( / )
Interword separation
spaces: ( ) ( ) ( )
Other typographer's marks
ampersand ( & ) asterisk ( * ) asterism ( ⁂ ) at ( @ ) backslash ( \ ) bullet ( • ) caret ( ^ ) currency (¤) dagger ( † ) ( ‡ ) degree ( ° ) interrobang ( ‽ ) number sign ( # ) pilcrow ( ¶ ) prime ( ′ ) section sign ( § ) tilde ( ~ ) underscore/understrike ( _ ) vertical line/pipe/broken bar ( \| ) ( ¦ )

A comma ( , ) is a punctuation mark. 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, some like a small filled-in number 9. It is used in many contexts, principally for separating things. According to the Oxford English Dictionary, the word "comma" comes directly from the Greek komma, which means "something cut off" or "a short clause".

1 Grammar
2 Numbers
3 Diacritic
4 Computer programming
5 American & British differences
6 References
7 External links

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Grammar

The comma has several uses in English grammar:

It is used to mark off separate elements in a sentence:
- introductory words and phrases
  - "Once upon a time, I didn't know how to use commas."
- parenthetical phrases
  - The parenthetical phrase is an important, often misunderstood use. It is often used for thought interruptions. Information that is unnecessary to the meaning of the sentence must be set off and enclosed by commas. If the information is necessary, no commas should be used.
    - For example, the sentences "I cut down all the trees, which were over six feet tall" and "I cut down all the trees that were over six feet tall" look similar but in fact have very different meanings. In the first sentence, all the trees were cut down, and a detail (that they were over six feet tall) is added. In the second, only some trees were cut down — those over six feet tall; there may have been shorter trees there, too, which were not cut down. In the first case, "which were over six feet tall" is set off by a comma because it is a non-restrictive clause (i.e., its removal doesn't alter the meaning of the sentence). In the second, "that were over six feet tall" is a restrictive clause and takes no comma (because if you left it out, the sentence would then say that all the trees were cut down, not just the ones over six feet).
  - Parenthetical phrases in sentences include explanations of noun subjects ("The film's star, Tom Cruise, said..."), years following dates (in American use) and months ("On December 7 1941, Pearl Harbor..." [see #7 below]), and states following cities ("John F. Kennedy was shot in Dallas, Texas, in 1963"). In each case, the parenthetical (as if in parentheses) is both preceded and followed by a comma.
The comma is also used to separate two independent clauses (a group of words that can function as a sentence) that are joined by a co-ordinating conjunction ("for", "and", "nor", "but", "or", "yet", and "so" when they are used to connect; the acronym "fanboys" can be used as a memory aid).
- "I passed the test, but he failed." — "I passed the test" and "He failed" can function as separate sentences
- "I walked home and left shortly after." — Although "I walked home" is independent, "left shortly after" is dependent on the first part of the sentence
Commas are used to separate items in lists. However, if the individual items in the list also contain commas, the list should be separated by a semicolon(";")
- A comma before the word "and" or "or" in a list of more than two things is called a serial comma, or an Oxford comma:
  - "We had tea, biscuits, and cake."
  - It is so named because its usage is recommended in the style guide of the Oxford University Press.
  - Although the Oxford comma is not always used, it is essential in certain sentences to avoid ambiguity.
    - "I spoke to the boys, Sam and Tom." — "The boys" refers to Sam and Tom.
    - "I spoke to the boys, Sam, and Tom." — "The boys", Sam, and Tom are separate units; thus four or more people were spoken to in all.
A comma may be used in a sentence before a quotation.
- Mr. Kershner says, "You should know how to use a comma."
  - An exception can be made if the sentence is structured as a single, fluid event: Mr. Kershner told me that I "should know how to use a comma." Also, some style guides prefer the use of a colon.
Commas are used in some (mostly English-speaking) countries to present large numbers in a more readable form.
- "1,000"
- "1,000,000"
Commas are used when writing names that are presented last name first.
- Bond, James
Two commas used when writing the date in the following forms:
- American English: September 11, 2001, was a momentous day.
- British English: Tuesday, 11 September 2001, was a momentous day.
A comma is written in an address between the city and the state:
- My dog's masseuse lives in New York, NY.
Fowler's Modern English Usage demonstrates an optional use of commas with two sentences, differing only by a comma:
- "The teacher beat the scholar with a whip". A simple description.
- "The teacher beat the scholar, with a whip". Expression of outrage.
  - This second example does not specifically require a comma, and is considered nonstandard usage.

The comma is easy to misuse in multiple ways; see comma splice.

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Numbers

In many European languages, commas are used as decimal separators. The only English-speaking country which uses this convention is South Africa. Thus, "1,5 V" means "one and one-half volts".

Another method of writing numbers is the international system writing style [1]. They write the number fifteen million as "15 000 000". The only punctuation mark is the decimal mark; a period in English text, a comma in all other languages (however ISO standards recommends the use of comma instead of points also in english speaking countries). For example, "twelve thousand fifty-one dollars, seven cents, and half a mill", is written in symbols as "$12 051.070 5" in English text, but "$12 051,070 5" in text of any other language.

In many places, English writers often put commas between each group of three digits. They would write the number fifteen million as "15,000,000". A number with a decimal does not use commas in the fractional portion. Thus, "twelve thousand fifty-one dollars, seven cents, and half a mill" is written in symbols as "$12,051.0705".

Historically, writers in many European languages used exactly the opposite convention. They would write the above quantities something like "15.000.000" and "₣12 051,070 5" [2].

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Diacritic

As a diacritic mark, comma is used in Romanian under s: Template:Polytonic (Template:Polytonic), and under t: Template:Polytonic (Template:Polytonic). A cedilla is occasionally used instead (notably in the Unicode glyph names), but this is technically incorrect.

Comparatively, some consider the diacritics on the Latvian consonants g, k, l, n, and formerly r to be cedillas. However from the typographical point of view they are commas. While their Adobe glyph names are commas, they name in the Unicode Standard is g, k, l, n, and r with cedilla. They were introduced to the Unicode standard before 1992 and their name cannot be altered.

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Computer programming

In computer programming, the comma corresponds to Unicode and ASCII character 44, or 0x002C.

In the C programming language, "," is an operator which evaluates its first argument (which presumably has side-effects) and then returns the value of its second argument. This is useful in "for" statements and macros. In many other computer languages (including C), commas are used to separate arguments to a function and to separate elements of a list.

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American & British differences

The comma and the quotation mark pairing can be used in several ways. In American English, the comma is to be included inside a quote (if a quote is present inside a sentence), no matter what the circumstances. For example:

My mother gave me the nickname "Johnny Boy," which really made me angry.

However, in British English, punctuation is only placed within inverted commas if it is part of what is being quoted or referred to. Thus:

My mother gave me the nickname "Johnny Boy", which really made me angry.

Barbara Child claims that in American English there is a trend toward a decreased use of the comma. (Child, 1992, p. 398) Lynne Truss says that this is equally true in the UK, and has been a slow, steady trend for at least a century: Template:Cquote

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