The 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 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 (linguistics) such as clauses, and lists of three or more things.

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. 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.

Uses

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 that 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.

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:

Use of serial comma disambiguating:

I spoke to the boys, Sam and Tom. – could be either the boys and Sam and Tom or the boys, who are Sam and Tom (I spoke to two people).

I spoke to the boys, Sam, and Tom. – could be the boys and Sam and Tom. Could also mean talking to a Sam about speaking to the boys and Tom.

Omission of serial comma disambiguating:

I thank my mother, Anne Smith and Thomas. – The writer is thanking three people: the writer's mother and Anne Smith (who is not the writer's mother) and Thomas.

I thank my mother, Anne Smith, and Thomas. – Could be either my mother and Anne Smith and Thomas or Thomas and my mother, who is Anne Smith.

At times the use of a serial comma can be essential to remove all ambiguity. For instance compare both of these two sentences:

I dedicate this book to my parents, Albert Einstein and JK Rowling.

and

I dedicate this book to my parents, Albert Einstein, and JK Rowling.

Although grammatically incorrect before dependent clauses, commas are often used to separate clauses; the first sentence could possibly be misinterpreted as a sentence with the proper nouns "Albert Einstein" and "JK Rowling" in the dependent clause clarifying the noun "parents" from the independent clause. This suggestion is eliminated with the addition of the second comma.

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.

If the individual items of a list are long, complex, affixed with description, 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 fed the cat, I brushed my clothes. (Compare 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.

Two independent clauses joined by a coordinating conjunction (for, and, nor, but, or, yet, so) or having a complementary relationship may sometimes be separated by commas, depending of preferred style, or a desire to overcome ambiguity. While many style guides call for commas, many authors omit them, particularly with short sentences. In Canada, the Editing Canadian English [5.7], the comma should be used between independent clauses introduced by conjunctions—such as and, but, or, not, for, yet—except in very short sentences. However, Canadian magazines and newspapers often omit this comma if there is no ambiguity of meaning.

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.

Certain adverbs

Commas are always used to set off certain adverbs: however, in fact, therefore, nevertheless, moreover, furthermore, still, instead, too (meaning 'also').

Therefore, a comma would be appropriate in this sentence.

If these adverbs appear in the middle of a sentence, they are enclosed in commas.

In this sentence, furthermore, commas would also be called for.

Using commas to offset certain adverbs is optional: then, so, yet.

So, that's it for this rule.

So that's it for this rule.

Parenthetical phrases

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 my 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.

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

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 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."

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: "On 19 December 1941 the Raid on Alexandria was carried out by Italian manned torpedoes."

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 writing addresses without any punctuation.

In numbers

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 full stops 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.

In names

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

Ellipsis

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.)

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.

Differences between American and British usage

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:

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 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:

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.

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, to separate elements in a list and to perform data designation on multiple variables at once.

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.

In Smalltalk, the comma operator is used to concatenate collections, including strings.

The comma-separated values (CSV) format is very commonly used in exchanging text data between database and spreadsheet formats.

==Diacritical usage== The comma is used as a diacritic mark in Romanian under the s (, ), and under the t (, ). A cedilla is occasionally used instead of it (notably in the Unicode glyph names), but this is technically incorrect. The symbol (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 (). The comma and the cedilla are both derivative of a small cursive z () 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 ascender. Other ascender letters with carons, such as letters ȟ (used in Finnish Romani and Lakota languages) and ǩ (used in Skolt Sami language), did not modify their carons to superscript commas.

See also

Cedilla

Ogonek

Semicolon

Serial comma

Decimal separator

References

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

Major Comma Uses

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.

The Ten Functions of Commas in English

Category:Punctuation Category:Alphabetic diacritics

ar:فاصلة ast:Coma (puntuación) az:Vergül bg:Запетая ca:Coma (puntuació) cs:Čárka (interpunkce) da:Komma de:Komma el:Κόμμα (στίξη) es:Coma (puntuación) eo:Komo eu:Koma (ikurra) fa:ویرگول fr:Virgule gl:Coma xal:Цеглгч ko:쉼표 (문장 부호) hr:Zarez id:Tanda koma is:Komma it:Virgola he:פסיק lv:Komats lt:Kablelis ln:Kóma hu:Vessző (írásjel) mk:Запирка ml:അല്പവിരാമം ms:Koma nl:Komma ja:コンマ no:Komma nn:Komma pl:Przecinek pt:Vírgula ro:Virgulă ru:Запятая sk:Čiarka (interpunkčné znamienko) sl:Vejica sh:Zarez fi:Pilkku sv:Kommatecken th:จุลภาค tr:Virgül uk:Кома (розділовий знак) war:Turook zh:逗號