Comma

For other uses, see Comma.

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 as a small, filled-in number 9.

The comma is used in many contexts, 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

The comma was one of the first punctuation marks. In the 3rd century BCE, 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 thousands of years 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 ( , ).

Grammar

The comma has several uses in English grammar, all related to marking-off separate elements within a sentence:

1. Introductory words and phrases: Once upon a time, I didn't know how to use commas.
2. Parenthetical phrases: The parenthetical phrase has an important, often misunderstood, use. It is often used for thought interruptions. Information that is unnecessary to the meaning of the sentence is commonly set off and enclosed by commas. If the information is necessary, no commas should be used.
   • Restrictive and non-restrictive use: 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, 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 does not 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 may include the following:
     • 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 ate the bagel, chewing with unbridled fury.
     • 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.
     • Any phrase that interrupts the flow of the main clause:
       • My father, chewing with unbridled fury, ate the bagel (free modifier).
       • My father, in a fit of rage, ate the bagel (prepositional phrase).
       • My father, with no regard for his health, ate the bagel (adverbial phrase).
       • My father, despite his lack of teeth, ate the bagel (adverbial phrase).
     • Years following dates (this is American usage - whether this is really parenthetical is moot): My father ate a bagel on December 7, 1941, and never ate one again. (See #10 below.)
     • States following cities: My father ate a bagel in Dallas, Texas, in 1963.
     • In each case, the parenthesised (as if in parentheses) text is both preceded and followed by a comma, unless that would result in doubling a punctuation mark, or if the parenthetical is at the start or end of the sentence.
3. The comma is often 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). Some people feel this is obligatory, while others prefer to use the comma only when not doing so would lead to a different reading.
   • I passed the test, but he failed. (comma) — I passed the test and He failed can function as separate sentences
   • I walked home and left shortly after. (no comma) — Although I walked home is independent, left shortly after is dependent on the first part of the sentence
4. The comma is often 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. (optional comma)
   • I lint-rollered my clothes after I brushed the cat. (no comma)
5. The comma is used to separate co-ordinate adjectives; that is, adjectives that directly and equally modify the following noun. Two questions can be asked to identify adjectives as coordinate adjectives:
   1. Would the meaning be the same if their order were reversed?
   2. Would the meaning be the same if and were placed between them?
   • A positive answer to either of these questions is evidence that a comma should be placed between the adjectives:
     • In the dull, incessant droning but not 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.
6. The comma is used to separate items in lists.

   

   • However, if any of the individual items in the list is complex and long, or contains a comma itself, it is best to use a semicolon (;) to separate the items, and possibly to introduce the list with a colon (:):
     • We had soup of the day; sole meunière, interestingly prepared with lime juice instead of lemon juice, and an unusual variety of parsley; a fruit salad; and a good port to finish off.
     • There were several tasks facing them: shaping the mast, for which they could use an adze or, with some difficulty, an axe; raising the finished mast; and caulking the timbers with whatever suitable material could be found.
   • A comma before the final and, or, or nor in a list of more than two things is called a serial comma or an Oxford comma:
     • We had milk, biscuits, and cream.
     • It is called the Oxford comma because the style guide of the Oxford University Press is one of its prominent advocates.
     • Although the Oxford comma is not always used, it should be applied to avoid ambiguity. Omitting the Oxford comma changes the meaning of a sentence, and unless the author is aware of the possible meaning the comma should be included rather than omitted.
       • 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.
       • I spoke to x, y and z. This sentence is stating that y and z are what comprise x.
       • I spoke to x, y, and z. This sentence is stating that x, y, and z were all spoken to and that they are different entities.
7. A comma is used to set off quoted material that is the grammatical object of an active verb of speaking or writing.
   • 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:
       • Wordsworth recalls his childhood existence as precious but as now outside his grasp: Where is it now, the glory and the dream?
     • Quotations that are incorporated in ways other than as the object of active verbs of speaking or writing should be punctuated the same as if there were no quotation marks: Mr. Kershner told me that I should know how to use a comma.
8. In representing large numbers, English texts use commas separating 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. Note, however, that in other-language texts the numerical use of commas and periods may be reversed (periods to group zeros, comma as decimal point). The International System of Units (SI) now recommends using spaces to separate sets of three digits in numbers more than four digits long (and the comma or period is then used only for the decimal place).
   • 6,345,990.01 (or 6 345 990.01 according to the SI)
   • 4123 (not 4,123 nor 4 123)
9. Commas are used when writing names that are presented last name first.
   • Smith, John
10. 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.
11. A comma is written in an address between the city and the state and again following the state):
    • My dog's masseuse lives in New York, NY, most of the year.
      • The following comma is commonly omitted by news agencies, but is a grammatical requirement per two rules: one, while considered necessary, the state functions parenthetically (New York city [in NY]) in that a preceding comma mandates a following comma; two, its omission serves incorrectly to separate the sentence (My dog's masseuse lives in New York and NY most of the year).
      • The USPS encourages no use of punctuations in address labels and everything to be in all caps. Thus, the address 1212 El Camino Real, San Bruno, California in postal form would be:
        1212 EL CAMINO REAL
        SAN BRUNO CA 94066
12. 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.
      • An alternative interpretation is that the second example represents a comma used to remove an ambiguity - to clarify that it was the teacher, not the scholar, who had the whip.
13. The comma is used to indicate that a word has been omitted (only if the reader will understand what the comma has replaced):
    • The cat was white; the dog, brown. (The comma clearly replaces "was".)

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

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 to be included inside a quotation, 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 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.

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 and has been a slow steady trend for at least a century:

Nowadays… A passage peppered with commas — which in the past would have indicated painstaking and authoritative editorial attention — smacks simply of no backbone. People who put in all the commas betray themselves as moral weaklings with empty lives and out-of-date reference books. (Truss, 2004, p. 97–98)

In his 1963 book, 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.

Diacritical usage

Main articles: S-comma and T-comma

The comma is used as a diacritic mark in Romanian under the s ([Ș] Error: {{Lang}}: text has italic markup (help), [ș] Error: {{Lang}}: text has italic markup (help)), and under the t ([Ț] Error: {{Lang}}: text has italic markup (help), [ț] Error: {{Lang}}: text has italic markup (help)). A cedilla is occasionally used instead of it (notably in the Unicode glyph names), but this is technically incorrect.

Comparatively, some consider the diacritics on the Latvian consonants ģ, ķ, ļ, ņ, and formerly ŗ to be cedillas. However, from the typographical point of view, they are commas. 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.

In numerals

Main article: Decimal separator

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. 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). Using this convention, twelve thousand fifty-one dollars, seven cents, and 5 mills, would be written in symbols as $12 051.075 in English text, but $12 051,075 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, 5 mills is written in symbols as $12,051.075.

Historically, writers in many European languages have used the exact opposite convention, writing the above quantities as 15.000.000 and $12.051,075.

Computer programming

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.

Bibliography

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

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

See also

• Cedilla
• Ogonek
• Semicolon

External links

• 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.