Some typefaces render it as a small line, slightly curved or straight, but inclined from the vertical; others give it the appearance of a miniature filled-in figure 9 placed on the baseline.
The word comma comes from the Greek κόμμα (kómma), which originally meant a cut-off piece, specifically in grammar, a short clause.
In Byzantine and modern copies of Ancient Greek, the "rough" and "smooth breathings" (ἁ, ἀ) appear above the letter.
In Latvian, Romanian, and Livonian, the comma diacritic appears below the letter, as in ș.
In spoken language, a common rule of thumb is that the function of a comma is generally performed by a pause.
In the 3rd century BC, Aristophanes of Byzantium invented a system of single dots (théseis) at varying levels, which separated verses and indicated the amount of breath needed to complete each fragment of the text when reading aloud.
The mark used today is descended from a /, a diagonal slash known as virgula suspensiva, used from the 13th to 17th centuries to represent a pause.
Commas are placed between items in lists, as in They own a cat, a dog, two rabbits, and seven mice.
No association with region or dialect is suggested, other than that its use has been strongly advocated by Oxford University Press.
It is recommended by the United States Government Printing Office, Harvard University Press, and the classic Elements of Style of Strunk and White.
Consider the following sentence: As a rule of thumb, The Guardian Style Guide[10] 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).
A relative clause takes commas if it is non-restrictive, as in I cut down all the trees, which were over six feet tall.
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.")
A comma splice should not be confused, though, with the literary device called asyndeton, in which coordinating conjunctions are purposely omitted for a specific stylistic effect.
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.
Additionally, most style manuals, including The Chicago Manual of Style[20] and the AP Stylebook,[21] recommend that the second element be treated as a parenthetical, requiring a second comma after: "The plane landed in Kampala, Uganda, that evening.
"[22] The United States Postal Service[23] and Royal Mail[24] recommend leaving out punctuation when writing addresses on actual letters and packages, as the marks hinder optical character recognition.
[25] Similar to the case in natural languages, commas are often used to delineate the boundary between multiple mathematical objects in a list (e.g.,
[26] In representing large numbers, from the right side to the left, English texts usually use commas to separate each group of three digits in front of the decimal.
It can also be used in regnal names followed by their occupation: Louis XIII, king of France and Navarre.
Commas are placed before, after, or around a noun or pronoun used independently in speaking to some person, place, or thing: In his 1785 essay An Essay on Punctuation, Joseph Robertson advocated a comma between the subject and predicate of long sentences for clarity; however, this usage is regarded as an error in modern times.
In Great Britain and many other parts of the world, punctuation is usually placed within quotation marks only if it is part of what is being quoted or referred to:[31][32][33] In American English, the comma was commonly included inside a quotation mark:[31][32] During the Second World War, the British carried the comma over into abbreviations.
[34] Western European languages like German, French, Italian, Spanish, and Portuguese use the same comma as English, with similar spacing, though usage may be somewhat different.
There are also a number of comma-like diacritics with "COMMA" in their Unicode names that are not intended for use as punctuation.
As such, the comma functions as a silent letter in a handful of Greek words, principally distinguishing ό,τι (ó,ti, 'whatever') from ότι (óti, 'that').
In Smalltalk and APL, the comma operator is used to concatenate collections, including strings.
In Czech and Slovak, the diacritic in the characters ⟨ď⟩, ⟨ť⟩, and ⟨ľ⟩ resembles a superscript comma, but it is used instead of a caron because the letter has an ascender.
In 16th-century Guatemala, the archaic letter cuatrillo with a comma (⟨Ꜯ⟩ and ⟨ꜯ⟩) was used to write Mayan languages.