One of the most intimidating grammar concepts for writers is correct comma usage. Saying “I thought there should be one” or “There seemed to be a pause” is not a good reason for using a comma. Properly used commas are important because they help the reader; without them, a reader would often have to backtrack and reread a sentence to find the writer’s meaning.
There are essentially six comma rules. Master these rules, and your writing will be easier to read.
Rule 1: Put a comma before for, and, nor, but, or, yet, so when they connect two independent clauses. An independent clause stands alone as a sentence.
- We lost our oars, and that was the end of our boating. (two sentences)
- We may leave Friday, or we may wait until Monday. (two sentences)
- I wanted to go but could not get my car started. (one sentence)
The last example does not have two independent clauses (it has just one subject and two verbs); therefore, no comma is necessary.
Rule 2: Put a comma between items in a series.
- We ordered eggs, bacon, hash browns, toast, and tomato juice for breakfast.
- She ended the conference call, picked up her briefcase, and left.
Adjectives in a series fall into two categories: coordinate and cumulative.
Coordinate adjectives modify the noun with equal weight and need commas:
- The red, white, and blue flag fluttered in the breeze.
- The fluffy, brown, angry cat hissed at me.
If the position of the adjectives could be moved and if the word and would fit naturally between them, you should probably use a comma.
Cumulative adjectives modify the noun so that the meaning builds and don’t need commas between them—even though they do make up a series.
- The mayor wore a dark blue wool jacket.
- The city demolished the dilapidated office building.
If an address or date is used in a sentence, treat it as a series, putting a comma after every item, including the last.
- They lived in Las Cruces, New Mexico, for two years.
- She was born on May 17, 1959, in Dobbs Ferry, New York, and grew up there.
When only the month and year are used in a date, the comma is usually omitted:
- He moved to Michigan in May 1980.
Rule 3: Put a comma after an introductory expression that does not flow smoothly into the sentence. It may be a word, a group of words, or a dependent clause.
- Yes, I'll go.
- Well, that was the end of that.
- Running down the hill, they slipped and fell.
- When everyone had left, the auditorium was locked.
A dependent clause at the beginning of a sentence usually needs a comma after it. In the last example, you can see that a comma is necessary. Otherwise, the reader would read “When everyone had left the auditorium . . .” before realizing that was not the writer’s meaning. A comma makes the reading easier.
Rule 4: Put commas around the name of a person spoken to.
- I think, Ky, that you are absolutely right.
- Lejla, how about a game of tennis?
- Happy anniversary, Mom and Dad!
Rule 5: Put commas around an expression that interrupts the flow of the sentence (however, moreover, finally, therefore, of course, by the way, on the other hand, I am sure, I think).
- He thought, however, that I should wait.
- I hope, of course, that they'll come.
- We grabbed our plates, therefore, and got in the buffet line.
- This should, I think, take only an hour.
Remember that some of the above words or phrases can be transitions (however, moreover, therefore, etc.), which often come between two independent clauses and require a semicolon in front of them.
- She was busy; however, she took time to help.
- It's an important meeting; therefore, I'm going.
Rule 6: Put commas around nonessential (extra or unnecessary) material.
Commas around nonessential phrases or clauses act like parentheses to bracket material that is not critical to the meaning of the sentence. The material may be interesting, but the main idea of the sentence would be clear without it.
- Dakota Simpson, who is heading the United Fund Drive, broke their ankle.
The clause who is heading the United Fund Drive is not essential to the main idea of the sentence. Without it, we still know exactly who the sentence is about and what exactly they did: Dakota Simpson broke their ankle. Therefore, the nonessential material is set off from the rest of the sentence by commas to show that it could be left out.
- The person who is heading the United Fund Drive broke their ankle.
The clause who is heading the United Fund Drive is essential to the main idea of the sentence. Without it, the sentence would read: The person broke their ankle. We would have no idea which person. The clause who is heading the United Fund Drive is essential because it tells us which person. It could not be left out of the sentence. Therefore, commas are not used around it.
- Like Water for Chocolate, a novel by Laura Esquivel, was translated into over 30 languages.
The words a novel by Laura Esquivel could be left out, and we would still know the main meaning of the sentence: Like Water for Chocolate was translated into over 30 languages. Therefore, the nonessential material is set off by commas to show that it could be left out.
- Laura Esquivel's novel Like Water for Chocolate was translated into over 30 languages.
The title of the novel is essential. Without it, the sentence would read: Laura Esquivel's novel was translated into over 30 languages. We would have no idea which of Laura Esquivel's novels was translated into over 30 languages. Therefore, the title could not be left out, and commas are not used around it.
Note: Comma rules change, and some commas that were once required can be omitted in certain circumstances. If you have doubts, consult a current grammar book or ask your instructor.
Learn more about "Commas: Three Simple Rules" by reviewing this handout.