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, or with the appearance of a small filled-in number 9.

The comma is used in many contexts and languages, principally 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.

History

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 (not to comply with rules of grammar, which were not applied to punctuation marks until much later). 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, though 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, notably by Aldus Manutius. In the 16th century, the virgule dropped to the bottom of the line and curved, turning into the shape used today ( , ).¹²³⁴

Uses

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.

In lists

Commas are used to separate items in lists, as in They own a cat, a dog, two rabbits and six mice. In English a comma may or may not 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 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, as in:

• I spoke to the boys, Sam and Tom. – The boys refers to Sam and Tom (I spoke to two people).
• I spoke to the boys, Sam, and Tom. – The boys, Sam, and Tom are separate units (I spoke to four or more people).

If the individual items of a list are long and complex or themselves contain commas, semicolons may be preferred as separators, and sometimes the list may be introduced with a colon.

Separation of clauses

Commas are often used to separate clauses. In English, a comma is generally used to separate a dependent clause from the independent clause if the dependent clause comes first: After I brushed the cat, I lint-rollered my clothes. (Compare I lint-rollered my clothes after I brushed 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 imply that only some of the trees – those over six feet tall – were cut down.)

Two independent clauses joined by a coordinating conjunction (for, and, nor, but, or, yet, so) may or may not be separated by commas, depending on preferred style, or sometimes a desire to overcome ambiguity.

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 is known as a comma splice, and is often considered an error in English.

Parenthetical phrases

Commas are often used to enclose parenthetical words and phrases within a sentence (i.e. information which 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, I didn't know how to use commas.⁵
• Address: My father ate the bagel, John.
• Interjection: My father ate the bagel, gosh darn it!
• Aside: My father, if you don’t mind my telling you this, ate the bagel.
• Appositive: My father, a jaded and bitter man, ate the bagel.
• Absolute phrase: My father, his eyes flashing with rage, ate the bagel.
• Free modifier: My father, chewing with unbridled fury, ate the bagel.
• Resumptive modifier: My father ate the bagel, a bagel which no man had yet chewed.
• Summative modifier: My father ate the bagel, a feat which no man had attempted.

Between adjectives

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:

• 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 quotes

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.

In dates

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 7, 1941. This style is common in American English. Additionally, most style manuals, including the Chicago Manual of Style⁶ and the AP Stylebook,⁷ recommend that the year be treated as a parenthetical, requiring a second comma after it: "Feb. 14, 1987, was the target date."

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 Style⁸ and the AP Stylebook,⁹ recommend that the second element be treated as a parenthetical, requiring a second comma after: "The plane landed in Kampala, Uganda, that evening."¹⁰

The United States Postal Service encourages the writing of address labels without any punctuation (and all in capital letters).

In numbers

Main article: Decimal separator

In representing large numbers, English texts use commas (or spaces) to separate each group of three digits. This is almost always done for numbers of six or more digits, and optionally for five (or even four) digits. (The SI writing style is to use spaces for this purpose.¹¹) However, in many other languages (and in South Africa) the comma is used as a decimal separator, equivalent to the decimal point.

In names

Commas are used when writing names that are presented last name first: Smith, John. They are also used before many titles that follow a name: John Smith, Ph.D.

Emphasis and clarity

Fowler's Modern English Usage demonstrates an optional use of commas in the following sentences:

• The teacher beat the scholar with a whip. A simple description.
• The teacher beat the scholar, with a whip. For emphasis, as an expression of outrage; or to clarify that it was the teacher, not the scholar, who had the whip.

Elision

Commas may be used to indicate that a word has been omitted, as in The cat was white; the dog, brown. (Here the comma clearly replaces was.)

Differences between American and British usage

The comma and the quotation mark pairing can be used in several ways. In American English, the comma (like most other punctuation marks) is included inside a quotation, no matter what the circumstances.¹² For example:

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

However, in British English, punctuation is only placed within quotation marks 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.

The use of the serial comma is sometimes perceived as an Americanism, but in fact 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.¹³ Lynne Truss says that this is equally true in the UK and has been a slow, steady trend for at least a century:

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 usually discarded.

Computing

In the common character encoding systems Unicode and ASCII, character 44 (0x002C) corresponds to the comma symbol.

In many computer languages commas are used to separate arguments to a function and to separate elements of a list.

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.

Diacritical usage (comma below)

Main articles: S-comma and T-comma

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. A consonant, ḑ / Ḑ (d with comma) was used in the Romanian transitional alpabet (XIXth century) to indicate the sound z where it was derived from cyrillic ѕ (/dz/). Ironically, both the comma and cedilla were independent derivatives of a small cursive z (ʒ) placed below the letter. Thus, in the case of Romanian, ș and ț are in origin shorthand for sz and tz.

Comparatively, some consider the diacritics on the Latvian consonants ģ, ķ, ļ, ņ, and formerly ŗ to be cedillas. Although their Adobe glyph names are commas, their names in the Unicode Standard are g, k, l, n, and r with cedilla. They were introduced to the Unicode standard before 1992, and their name cannot be altered.

In the Czech and Slovak languages, the diacritics in the characters ď, ť, and ľ resemble superscript commas, but they are modified carons.

References

1. ^ Reading Before Punctuation – Introduction to Latin Literature pamphlet, Haverford College
2. ^ A History Of Punctuation
3. ^ Points to Ponder – STSC Crosstalk
4. ^ Manuscript Studies, Medieval and Early Modern – Paleography: Punctuation glossary
5. ^ Garner's Modern American Usage, (Oxford: 2003, p. 655)
6. ^ "It’s conventional to put a comma after the year. The commas are like parentheses here, so it doesn’t make sense to have only one.” "Chicago Style Q&A: Commas". The Chicago Manual of Style Online. Retrieved on 2008-10-29.
7. ^ "When a phrase refers to a month, day and year, set off the year with commas... Feb. 14, 1987, was the target date." "Ask the Editor". AP Stylebook. Retrieved on 2008-10-29.
8. ^ "Mary traveled to Seattle, Washington, before going on to California.” "Chicago Style Q&A: Commas". The Chicago Manual of Style Online. Retrieved on 2008-10-29.
9. ^ "Acme Pens was founded in Padua, Italy, in 2004." "Ask the Editor". AP Stylebook. Retrieved on 2008-10-29.
10. ^ Chicago Manual of Style, 14th ed., §5.67.
11. ^ Institute of Electrical and Electronics Engineers, Inc.
12. ^ See, for example, the Chicago Manual of Style
13. ^ Robert J. Samuelson (2007-23-2007). "The Sad Fate of the Comma", Newsweek, p. 41. Retrieved on 18 July 2007. 

• This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

See also

• Cedilla
• Ogonek
• Semicolon
• Serial comma

Bibliography

• Barbara Child, Drafting Legal Documents, 2nd Edition, 1992.
• Lynne Truss, Eats, Shoots and Leaves, Gotham Books (2004), ISBN 1-59240-087-6.

External links

• Commas: They're Not Just for English Majors, Anymore
• English comma rules and exercises
• Rules governing comma usage
• Major Comma Uses
• Rules for Comma Usage
• Notes on Commas
• Comma guidelines – also helpful for non-native speakers
• Grammar, Punctuation, and Capitalization – a comprehensive online guide by NASA
• The Oxford Comma: A Solution – a satirical suggestion to settle the problem of the Oxford Comma once and for all.
• The Quotta and the Quottiod – another satirical compromise between the American and British traditions relating to quotes and commas.