It's easy to see how commas are probably the most misused punctuation mark. Not only are they tricky to use, but there are so many rules revolving around them, it's difficult to keep them straight. Commas are mainly used to join two clauses together to form a sentence, but they are also used with appositives and clauses; definitive words and titles; and times, places, and ideas. So how do you keep all this information straight? I recommend splitting the rules into categories; it's much easier to memorize a few categories than it is to remember all the rules individually. I also recommend studying the rules on a regular basis. I know the last thing most people want to do is to spend their free time schooling themselves again, especially about something as tedious as grammar. But if you don't practice, you'll never get any better.
Appositives and Clauses
1. Use a comma to set off nonessential information within a sentence. This type of appositive would be nonrestrictive.
Example: Jamie, my lab partner, got high marks in chemistry last year.
If the information is extra but necessary to the meaning of the sentence, the appositive is considered restrictive; therefore, no commas are used.
Example A: Famous artist Vincent Van Gogh was of Dutch descent.
Example B: Johnny brought his dog Spot to the park.
Why are these sentences restrictive? Example A mentions a specific famous artist. Without the name of that artist, the reader wouldn't know who was of Dutch descent. Example B assumes that Johnny has more than one dog. Therefore, clarification is needed to name which dog Johnny brought to the park with him. The same would be true if the subject had more than one sister or brother, car, etc.
2. Use a comma to separate two independent clauses joined by a coordinating conjunction. Note that the use of a conjunction alone does not make both parts independent. If a period can replace the conjunction and both parts of the sentence can stand alone, then both clauses are independent. If the second part cannot stand alone, it is a dependent clause, so no comma is needed.
Example A: Johnny went left, and I went right. Example B: Johnny went left but didn't bother to say goodbye.
Check out the following site for a list of coordinating conjunctions and their uses: http://bit.ly/MTurN
3. Use a comma after an introductory/subordinating word or phrase, otherwise known as a dependent clause, at the beginning of a sentence. The only exception to this rule is if the phrase is an adverbial phrase immediately followed by the verb it modifies.
Example A: After a long walk in the park, Walter was able to calm down.
Example B: Yes, I told him we would meet later. Example C: Before him stood a grand entrance. (The adverbial phrase "before him" modifies "stood.")
Check out this site for a list of subordinating conjunctions: http://bit.ly/53JG2x
Definitive Words and Titles
4. Use commas to set off names and titles that directly address someone, as well as degrees following names.
Example A: My wife, Tina, makes delicious chocolate chip cookies.
Example B: Miss, would you like a hand?
Example C: Doctor Colby Smith, M.D., has received many awards for his medical expertise.
5. Use a comma around interrupter words and phrases (considered a type of non-restrictive appositive) that appear in the middle of a sentence. Prepositional phrases can also sometimes be interrupters.
Example A: This afternoon, in fact, we had gorgeous weather.
Example B: Alex, however, did not want to participate.
Example C: I found out, to my horror, that I was failing English.
However, when interrupter words and phrases are placed in the middle of two independent clauses, a conjunction, period, or semicolon should be used.
Example A: We were running low on food, but the store was nearby.
Example B: We were running low on food. However, the store was nearby.
Example C: We were running low on food; however, the store was nearby.
In these examples, using a comma alone would result in a common error called a comma splice. A comma splice occurs when two independent thoughts are joined together by a comma alone, rather than using a conjunction, period, or semicolon. This can occur with or without an interrupter word. Note that when an interrupter word is used in this kind of a situation, a comma must follow it.
6. Use a comma between coordinate adjectives. To decide if the adjectives are coordinate, ask yourself the following two questions:
- Does the word "and" make sense between them?
- Does the sentence make sense if the two adjectives are written in reverse order?
If the answer is yes to both of these questions, the adjectives are coordinate, and a comma should be used. If not, the adjectives are considered non-coordinate, and the comma is omitted.
Example A: Before her stood a tall, white fence.
Example B: Tom found fresh green grass on the other side of the hill.
7. Use a comma to separate words or short phrases that are part of a list. Use a semicolon to separate longer phrases used as list items.
Example A: I went to the store and bought milk, eggs, bread, and butter.
Example B: I still need to brush my teeth, comb my hair, and get dressed.
Example C: To learn how to use punctuation effectively, one must study it frequently and take note of any changes to the rules; practice it in both daily writing and in professional settings; and be willing to change their habits if they are using punctuation incorrectly.
With simple lists, bear in mind that U.K. rules and U.S. rules differ. In the U.K., there is no comma before the "and" (known as the Oxford comma); in the U.S., there is. You may see the comma omitted in the U.S. for news articles and other such areas of journalism, but in fiction writing and most of nonfiction writing, the comma still stands.
Times, Places, and Ideas
8. Use a comma between the day of the month and the year. If either the day of the month or the year is omitted, do not use a comma.
Example A: I was born on January 12, 1927.
Example B: I was born in January 1927.
Example C: I was born on January 12.
9. Use a comma to separate city and state.
Example: She was born in Lexington, Kentucky.
10. Use a comma to set off a direct quote. When splitting a sentence that contains a direct quote, place a comma before both halves of the quote.
Example A: John said, "It's your turn to wash the dishes."
Example B: "How is it my turn," Mary complained, "when I did them last night?"
11. Use a comma to separate a statement from a question when they are both part of the same sentence.
Example: I can go with my friends, can't I?
12. Use a comma to separate contrasting parts of a sentence.
Example: I prefer to have my beverages shaken, not stirred.
Though seldom needed, commas can sometimes be used for clarification. If you are a native speaker of English, recognizing the need for such a comma will come a bit more easily. Even so, developing the necessary intuition to recognize these situations can be difficult. The following is an example of how to deal with such a sentence.
Unclear: The room was full of crying babies and mothers. (Were the mothers crying too?)
Better: The room was full of crying babies, and mothers. (Clearer, but let's make it even better.)
Best: The room was full of mothers and crying babies.
As you can see from the examples above, the best option is to reword the sentence entirely.
Quick Overview of Commas
- Commas are used to set off nonessential information.
- Use commas to separate two independent clauses joined by a coordinating conjunction.
- Use commas after introductory clauses, except in the case of adverbial phrases immediately followed by the verb they modify.
- Use commas to set off names, titles, and degrees.
- Use a comma between coordinate adjectives.
- Use a comma to separate day of the month and year.
- Use a comma to separate city and state.
- Use commas to set off direct quotes.
- Use a comma to separate a statement from a question and between contrasting parts of a sentence.
- Use commas sparingly for clarification.