10 Functions of the Comma

By Mark Nichol

A comma is a versatile punctuation mark, serving ten basic functions. Here’s an enumeration, with examples.

1. Separate the elements in a series: “Groucho, Harpo, and Chico developed the philosophy called Marxism.”

Many periodicals and websites, and most colloquially written books, omit the serial, or final, comma, but it is all but mandatory in formal writing and is recommended in all usage. As language maven Bryan Garner observes, “Omitting the serial comma may cause ambiguities, whereas including it never will.”

2. Separate coordinated independent clauses: “I like the Marx Brothers, but she thinks they’re too silly.” (An independent clause is one that can stand on its own as a sentence but is linked with another by a conjunction and/or a punctuation mark.)

Exceptions include sentences with closely linked clauses (“Go to the window and see who’s there”) and those with a compound predicate (“The Marx Brothers are known for their puns and their sight gags”).

3. Separate an introductory word (“Naturally, I agree with you”), phrase (“Last summer, I went on a long vacation”), or subordinate clause (“If you’re too busy now, wait until later”) from the remainder of the sentence.

4. Separate an optional parenthetical element from the remainder of the sentence. “We have, in a manner of speaking, won despite our loss.” (The phrase “in a manner of speaking” could also be set off by em dashes or parentheses, depending on whether the writer wishes to emphasize the interruption of the statement “We have won despite our loss” or wants to diminish it as an aside.)

5. Separate coordinate adjectives from each other: “I could really use a tall, cool drink right now.” (Do not separate noncoordinate adjectives with a comma; this post explains the difference between these two types of adjectives.)

6. Separate an attribution from a direct quotation: “She said, ‘Neither choice is very appealing’”; “‘That’s not my problem,’ he replied.” (A colon may be precede a formal pronouncement or an attribution that forms a complete thought, as in, “He had this to say: ‘Her point is irrelevant.” Omit punctuation when the attribution is implied, as in “Your response ‘Her point is irrelevant’ is evasive.”)

7. Separate a participial phrase or one lacking a verb from the remainder of the sentence: “Having said that, I still have my doubts”; “The deed done, we retreated to our hideout.”

8. Separate a salutation from a letter (“Dear friends,”) or a complimentary close from a signature in a letter (“Sincerely,”). A colon should be used in place of a comma in a formal salutation.

9. Separate elements when setting off a term for a larger geopolitical entity from that for a smaller one located within it (“Santa Barbara, California, is located on the coast”) and for elements of street addresses (“1600 Pennsylvania Avenue, Washington, DC”) (and dates (“January 1, 2013”).

10. Separate groups of three digits in numbers: (Let me tell you how to make your first 100,000,000 dollars.” (Because large numbers are difficult to scan, it’s usually better to use one of the following forms: “100 million dollars,” “one hundred million dollars.”)

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8 Responses to “10 Functions of the Comma”

  • Paul Kelly

    I recommend omitting the serial comma if you’re following AP Style. It’s not a matter of choice: It’s a rule.

  • Nhlanhla Sihlophe

    Please advise, I need to know as to which of the functions of a comma does the punctuation in the sentence below fit in. The editor of a document I wrote some time ago suggested that I punctuate this sentence as indicated below, but, as a second language writer, I always find it difficult to decide on whether to punctuate like this or not. Which rule do I apply? Please help.

    “Chapter 5 of NEMA provides for activities which may significantly impact on the environment, to be identified by the Minister of Environmental Affairs as requiring authorisation prior to implementation.”

  • Dale A. Wood

    “Many periodicals and websites, and most colloquially written books, omit the serial, or final, comma, but it is all but mandatory in formal writing and is recommended in all usage.”

    That “final comma” is required by the OXFORD University writing guide in the U.K., hence that comma is widely used there.

    On the other hand, many Britons thumb their noses at Oxford University, the United States, Canada, etc.

    I am very much against that. Things should be written the Oxford way, the American way, and the Canadian way. I agree with Mr. Nichol whole-heartedly here.

  • Jeremy Porter

    My understanding is that outside the US the serial comma (or Oxford comma) is only recommended to avoid ambiguity. I’ve worked in New Zealand, Australia, Canada and the UK and the standard in those countries was not to use it. I have noticed in the US that everyone seems to include it. Might be worth clarifying for the international readers.

  • Mark Nichol


    That is, in essence, what I wrote. The presence or absence of the serial comma depends on style, whether your own or from a style guide. The style for formal writing, as expressed in The Chicago Manual of Style and similar resources, is to use a serial comma. The style for journalistic writing, as expressed in The Associated Press Stylebook, is to omit it. However, I recommend it in all usage.

  • Alice Kemp

    Hi there!
    My writing question involves salutations, viz. how do you write, say, a semi-formal salutation to a person whose name you don’t know and, if part of an organization, whose postion or title you don’t know? I encounter this quandry particularly in addressing email responses to freelance job offers on the Internet. For example, a person whose gender I don’t even know, advertises for a freelance writer and does not leave his/her name. What salutation should I use in responding to such a request?

    Thank you so much. I do enjoy your daily writing tips and have found many of them quite useful.

  • Steve Maurer

    Actually, omitting the comma before the conjunction in a series is considered correct when using the Associated Press Stylebook for a guide. If omitting the comma creates confusion, the AP Stylebook then recommends using it.

    The Chicago Manual of Style requires the comma before the conjunction.

    Therefore, the first of your comma uses depends on the type of writing you are doing.

  • Bobby

    I have a couple of questions.
    1. Is the second part in this sentence, which you used as an example in your blog, a separate coordinated independent clause if it cannot stand on its own. I mean can ‘and their sight gags’ stand on its own withoug a verb. You gave this as an example where the coordinated independent clause is closely related and thus does not need a separating comma, correct?
    “The Marx Brothers are known for their puns and their sight gags”

    2. I didn’t quite understand what you mean here. ‘A colon may be precede a formal pronouncement or an attribution that forms a complete thought’

    Pardon me for any language mistakes as I am not a native English speaker.

    Thank you!

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