Commas
Commas and periods are the most frequently used punctuation marks. Readers rely on commas
to help them know when words in a sentence belong together. The placement of most commas is
rule-based, but sometimes they are optional. The following rules cover most uses of the comma.
Rule 1. Use commas to separate words and word groups in a simple series of three or more items.
Example: My estate goes to my husband, son, daughter-in-law, and nephew.
When the last comma in a series comes before and or or (after daughter-in-law in the above example), it is
known as the Oxford comma. Most newspapers and magazines drop the Oxford comma in a simple series.
Omitting the Oxford comma, however, can sometimes lead to misunderstandings.
Example: Jean sat on a blanket by the lake with her ex-boyfriend, a pastry chef and a dog walker.
With only one comma, the sentence is unclear: Is Jean sitting on a blanket with one other person or three?
Fiction and nonfiction books generally prefer the Oxford comma. Writers must decide Oxford or no Oxford and
should not switch back and forth.
Rule 2. Use a comma to separate two adjectives when the adjectives are interchangeable.
Example: He is a strong, healthy man.
We could also say healthy, strong man.
Example: We stayed at an expensive summer resort.
We would not say summer expensive resort, so no comma.
Rule 3a. Many inexperienced writers run two independent clauses together by using a comma instead of a period.
This results in the dreaded comma splice.
Incorrect: He walked all the way home, he shut the door.
There are several simple remedies:
Correct: He walked all the way home. He shut the door.
Correct: After he walked all the way home, he shut the door.
Correct: He walked all the way home, and he shut the door.
Rule 3b. In sentences where two independent clauses are joined by connectors such as and, or, but, etc., put a
comma at the end of the first clause and before the connector.
Incorrect: He walked all the way home and he shut the door.
Correct: He walked all the way home, and he shut the door.
Some writers omit the comma if both clauses are short:
Example: I paint and he writes.
If there is no independent clause after the connector, a comma is generally unnecessary.
Example: He thought quickly but still did not answer correctly.
Rule 4a. Use a comma after certain words that introduce a sentence, such as well, yes, why, hello, hey, etc.
Example: Why, I can't believe this!
Example: No, you can't have a dollar.
Rule 4b. Use commas to set off expressions that interrupt the sentence flow (nevertheless, after all, by the way, on
the other hand, however, etc.) or present a contrast. Also use commas with dates, locations, and titles, as in
these examples:
Example: I am, by the way, very nervous about this.
Example: I can go, can’t I?
Example: Will you, Aisha, do that assignment for me?
Example: It was in the newspaper’s June 5, 2003 edition.
Example: He grew up in Akron, Ohio.
Example: Al Mooney, M.D. is here.
Rule 5. When starting a sentence with a dependent clause, use a comma after it.
Example: If you are not sure about this, let me know now.
But often a comma is unnecessary when the sentence starts with an independent clause followed by a
dependent clause.
Example: Let me know now if you are not sure about this.
Rule 6. Use commas to set off nonessential words, clauses, and phrases. If something or someone is sufficiently
identified, the description that follows is considered nonessential (it can be removed from the sentence without
fundamentally altering the meaning) and should be surrounded by commas. If the description is essential (it
cannot be removed), then do not use commas.
Example: My brother Bill is here.
Now, see how adding commas changes the sentence's meaning:
Example: My brother, Bill, is here.
Careful writers and readers understand that the first sentence means I have more than one brother. The
commas in the second sentence mean that Bill is my only brother. Why? In the first sentence, Bill is essential
information: it identifies which of my two (or more) brothers I'm speaking of. This is why no commas enclose Bill.
In the second sentence, Bill is nonessential information—whom else but Bill could I mean?—hence the
commas. In the following example, who has a limp is essential information and so no commas are used:
Example: The boy who has a limp was in an auto accident.
We do not know which boy is meant without further description; therefore, no commas are used.
Comma misuse is nothing to take lightly. It can lead to a train wreck like this:
Example: Mark Twain's book, Tom Sawyer, is a delight.
Because of the commas, this sentence states that Twain wrote only one book. In fact, he wrote more than two
dozen of them.
Following are two instances of the need for an appositive comma with one or more nouns. Don’t forget the
second comma:
Incorrect: My best friend, Joe arrived.
Correct: My best friend, Joe, arrived.
Incorrect: The three items, a book, a pen, and paper were on the table.
Correct: The three items, a book, a pen, and paper, were on the table.
Rule 7. Use commas to introduce or interrupt direct quotations.
Example: He said, "I don't care."
Example: "Why," I asked, "don't you care?"
Rule 8. Use a comma before and after certain introductory words or terms, such as namely, that is, i.e., e.g., and for
instance, when they are followed by a series of items.
Example: You may be required to bring many items, e.g., sleeping bags, pans, and warm clothing.
Rule 9. Use a comma before the term etc.; if it is placed midsentence, commas should enclose it.
Example: Sleeping bags, pans, warm clothing, etc., are in the tent.
