Comma

The comma (,) is a punctuation mark shaped like a little left-oriented drop, placed on the baseline of the text and used in many writing systems to indicate a pause in a sentence or to separate things; in a few languages, it also serves as a diacritic mark below a letter (for instance: ș, ț).

Use as a punctuation mark

In English

Commas are used exclusively as punctuation marks in modern written English, a language in which diacritical marks are not used.

One conventional use of commas is in separation of a list of items:

one, two, three and four

That example also illustrates one of the discretionary uses of commas. The same list might also be written with a comma, known as a serial comma, after the penultimate item in the list:

one, two, three, and four

The serial comma is particularly useful when the items in the list are lengthy.

Another conventional use of commas in English is separation of groups of numerals into groups of three. For example, the numeral "ten thousand" is ordinarily written:

10,000

and one hundred thousand is written:

100,000

Commas also figure routinely in some dating schemes. Most people in the U.S. tend to write dates in the form:

July 4, 1776

British, European and other writers are more likely to write:

4 July 1776

normally without a comma after the month.

The comma is used before vocatives:

Hi, Peter. Thanks, Jill.

This comma is sometimes omitted in informal contexts, such as internet chat, but it is correct to include it.

Use as a diacritic mark

In Romanian

As a diacritic mark, the comma below ș and ț occurs mainly in Romanian (a Romance language):

• ș is pronounced [ʃ] (in contrast with s pronounced [s])
• ț is pronounced [ts] (in contrast with t pronounced [t])

The comma below is often replaced by a cedilla (ș and ț becoming ş and ţ) but in an accurate typography, the comma should be preferred. This is a computing input problem, especially due to an error of the first Unicode conventions. Since the end of the 2000's, later versions of Unicode and of various operating systems have tended to resolve this problem by providing an accurate comma on ș and ț.

It has to be noted that other languages use a cedilla on ş and not a comma (Turkish, Azeri, Volga Tatar, Crimean Tatar, Gagauz, Turkmen, Kurdish).

In Latvian

In Latvian (a Baltic language), a sort of comma is found on the following palatal consonants:

• ģ with a turned comma above (uppercase: Ģ with a comma below) is pronounced [ɟ] (in contrast with g pronounced [g])
• ķ is pronounced [c] (in contrast with k pronounced [k])
• ļ is pronounced [ʎ] (in contrast with l pronounced [l])
• ņ is pronounced [ɲ] (in contrast with n pronounced [n])
• the former letter ŗ is no longer in use and is replaced by r.

It is not always clear whether the diacritic is a comma or a cedilla. Some specialists state that the comma should be preferred in a good typography.