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".

Grammar

It is used to mark off separate elements in a sentence: introductory clauses, words in a series, parenthetical phrases, or interjections.

Commas are also used to separate items in lists, and to present large numbers in a more readable form.

These formal uses frequently also indicate a pause in speech. Writers often use optional commas for stylistic reasons, to indicate such a pause where none may be required, grammatically.

Fowler's Modern English Usage demonstrates this 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.

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.

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

Numbers

In many European languages, commas are used as decimal points. Thus, "1,5 V" means "one and one-half volts". However, commas are never used this way in English, except in South Africa.

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. 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].

Diacritic

As a diacritic mark, comma is used in Romanian under s: Ș (ș), and under t: Ț (ț). 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 commas as well. While their Adobe glyph names are commas, they are actually cedillas.

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.

References

External links

• English comma rules
• Rules governing comma usage