Uses of the Comma

Commas are used after introductory clauses and phrases, to set off interruptions within the sentence, with nonrestrictive phrases and clauses, and between items or modifiers in a series. Commas can also join independent clauses as long as the comma is followed by a coordinating conjunction ( for, and, nor, but, or, yet, so).

There are special situations in which commas should also be used. For example, use commas with quotations, dates, addresses, locations, and numbers with four or more digits. Commas should never be used around restrictive clauses, to separate a subject and verb, or to separate a verb and its direct object.

As you learn about commas, first, recognize that they signal a pause; second, know which rules can be bent without misleading your reader. Commas are the most frequently used internal punctuation in sentences, and people have more questions about them than about any other punctuation mark. One reason is that different editors have different opinions about when a comma is needed. You're likely to read one book in which commas abound, while in another text, they are scarce. The trend has been toward fewer commas.

Sometimes a comma is absolutely necessary to ensure the meaning of a sentence, as in the following examples.

Because I wanted to help, Dr. Hodges, I pulled the car over to the side of the road.
Because I wanted to help Dr. Hodges, I pulled the car over to the side of the road.

In the first sentence, the pair of commas indicates that Dr. Hodges is being addressed. In the second sentence, Dr. Hodges is the one receiving the help. Most situations, however, aren't this clear.

Joining independent clauses

Generally, when you join independent clauses with a coordinating conjunction, insert a comma before the conjunction.

Ryan never answered these charges, but he was later forced to give up part of the money.
The novel lacks fully developed characters, and the plot is filled with unlikely coincidences.

If the two independent clauses are short and closely related, you may use a comma or omit it, depending on whether or not you want to indicate a pause.

It was an admirable scheme and it would work.
OR It was an admirable scheme, and it would work.
The night was cold and the sky was clear.
NOT The night was cold, and the sky was clear.

When you insert a comma between independent clauses, it must be accompanied by one of the coordinating conjunctions. If it isn't, you create a comma splice.

It had been a tumultuous year that had taken everybody by surprise, and it left the revolutionaries worse off than they had been before.
NOT It had been a tumultuous year that had taken everybody by surprise, it left the revolutionaries worse off than they had been before.

After introductory clauses

It is customary to use a comma after an introductory adverbial clause. With a lengthy clause, the comma is essential.

After she walked into the room, we stopped gossiping.
If you receive inappropriate material, acknowledge it by explaining to the correspondent why the material won't see print.

You may omit the comma if the subordinate clause is short and if there is no possibility for miscommunication.

When she arrived we stopped gossiping.
After I turned sixteen I was allowed to stay out until midnight.

Sometimes omitting a comma will cause confusion or amusement, as in the following example.

When we are cooking the children cannot come into the kitchen. (no)
When we are cooking, the children cannot come into the kitchen. (yes)

Remember that, unlike a clause, a phrase is a group of words without a subject and a verb.

If an introductory phrase is more than a few words, it's a good idea to follow it with a comma. Always use a comma if there is any possibility of misunderstanding the sentence without one.

By taking the initiative to seek out story leads, a reporter will make a good impression on the editor.
At the beginning of the visiting professor's lecture, most of the students were wide awake.
Unlike many performances of the symphony, this one was spirited and lively.
Before eating, Cameron always runs two miles on the beach.

Note that the introductory phrase in the last example, although short, would lead to a misunderstanding if the comma were omitted.

A participial phrase at the beginning of a sentence is always followed by a comma.

Smiling and shaking hands, the senator worked her way through the crowd.

Do not confuse a participial phrase with a gerund phrase, however. A gerund phrase that begins a sentence should not be followed by a comma. Compare the following two sentences.

Thinking of the consequences, she agreed not to release the memo to the press. (introductory participial phrase, modifying she: use a comma)
Thinking of the consequences gave her a tremendous headache. (gerund phrase, functioning as the subject of the sentence: do not use a comma)

Use of a comma after most short introductory phrases is optional.

Later that day Jack and Linda drove to the ocean.
After the main course I was too full for dessert.

The best way to decide whether to use a comma is to read the sentence aloud and see if you pause after the introductory phrase. If you pause, use a comma.

To set off interrupting elements

Some phrases, clauses, and terms interrupt the flow of a sentence and should be enclosed in commas. Examples of these interrupters are conjunctive adverbs, transitional phrases, and names in direct address.

Conjunctive adverbs and transitional phrases— consequently, as a matter of fact, of course, therefore, on the other hand, for example, however, to tell the truth—are usually followed by commas when they begin sentences.

For example, you shouldn't use an acid solution on soft surfaces.
Therefore, he refused to go with us.

When they interrupt a sentence, they are usually enclosed in commas.

As the project moves along, of course, you will be given greater independence.
One who excels at research, for example, might be assigned to the library.

A name or expression used in direct address is always followed by a comma, or enclosed in commas when it interrupts the sentence.

Fellow citizens, I am here to ask for your support.
I tell you, Jason, I will not be forced into this by you or anyone.
Yes, readers, I am telling you the truth.

Other interrupters may also require commas. Check your sentence for elements outside the main flow of the sentence and enclose them in commas.

It is too early, I believe, to call in the police.
The historical tour, we were led to believe, was organized by experts.

Although dashes and parentheses can also be used to set off some kinds of interrupting elements, commas are better when you want to draw less attention to an interruption.

With restrictive and nonrestrictive elements

Look at the following two sentences. In the first sentence, who arrived yesterday is a restrictive clause—that is, one that restricts, limits, or defines the subject of the sentence. In the second sentence, the same clause is nonrestrictive—that is, it doesn't restrict or narrow the meaning but instead adds information. A restrictive element is essential to the reader's understanding; a nonrestrictive element is not.

The women who arrived yesterday toured the island this afternoon.
The women, who arrived yesterday, toured the island this afternoon.

In the first sentence, who arrived yesterday defines exactly which women are the subject of the sentence, separating them from all other women. In the second sentence, the information who arrived yesterday is additional information but is not essential to the meaning of the sentence. It does not separate the women from all other women. As the writer, you must decide which kind of information you intend.

Commas make all the difference in meaning here. Restrictive (or essential) elements should not be enclosed in commas, while nonrestrictive (or nonessential) elements should be. Review the following sentences.

The workers who went on strike were replaced. (restrictive)
The workers, who went on strike, were replaced. (nonrestrictive)

In the first sentence, only some workers were replaced. The absence of commas restricts the subject to only those workers who went on strike. In the second sentence, all the workers were replaced. The information that they went on strike is not essential; it doesn't define which workers were replaced.

In the following sentence, the phrase who are over age sixty is essential in limiting the subject workers and therefore should not be enclosed in commas. The second sentence means that all workers are over age sixty, which isn't logical.

Workers who are over age sixty have difficulty finding a new job.
NOT Workers, who are over age sixty, have difficulty finding a new job.

Whether to use commas around modifying elements is based entirely on whether the element is restrictive (essential or limiting) or nonrestrictive (additional information).

My brother, who is thirteen, watches television more than he reads. (additional information)
The man who took the pictures is being sued for invasion of privacy. (essential)
Cats, more independent than dogs, are good pets for people who work all day. (additional information)
Cats who are fussy eaters are a trial to their owners. (essential)
My brother, while swimming in the ocean, saw a jellyfish. (additional information)
People swimming in the ocean should watch for jellyfish. (essential)

With appositives

Appositives are words that restate or identify a noun or pronoun. When appositives are nonrestrictive, they are enclosed in commas.

Kublai Khan, grandson of Genghis, was the first Mongol emperor of all China.
Jack Kerouac, one of the most famous of the Beat Generation writers, came to symbolize the era he wrote about.

Sometimes an appositive is essential because it limits the subject. It must not be enclosed in commas. Look at the following examples.

Shakespeare's play Hamlet was probably written about 1600.
NOT Shakespeare's play, Hamlet, was probably written about 1600.

In this example, if you enclose Hamlet in commas, you limit the meaning and communicate that Shakespeare wrote only one play.

Between items in a series (serial comma)

It is considered standard practice to use commas to separate items in a series, called a serial comma (example: red, white, and blue). Although some editors feel that it is acceptable to omit the final comma in a series, it's clearer and easier to consistently insert the comma before the final element.

He bought a dishwasher, microwave, refrigerator, and washer from the outlet store.
Her play is filled with coincidences, false anticipations, and nonresponsive dialogue.

Omitting a final comma may create ambiguity. Since you should be consistent throughout a piece of writing, you might want to get in the habit of always using the serial comma.

The following examples show the serial comma separating a series of items.

The millionaire's estate was to be divided among his housekeeper, the gardener, his sons, and the grandchildren.
The recipe said to mix the flour, sugar, eggs, and milk together.
She warned us about the subway, the elevators at Bloomingdale's, and the Metropolitan Museum of Art.

The following examples do not have the serial comma and can be ambiguous in meaning.

The millionaire's estate was to be divided among his housekeeper, the gardener, his sons and the grandchildren.
The recipe said to mix the flour, sugar, eggs and milk together.
She warned us about the subway, the elevators at Bloomingdale's and the Metropolitan Museum of Art.

Don't use commas if all items in a series are joined by and or or.

He asked to see Martha and Helen and Eileen.
NOT He asked to see Martha, and Helen, and Eileen.

Between modifiers in a series

Modifiers in a series are usually separated with commas. But don't put a comma between the final modifier and the word it modifies.

It was a dark, gloomy, forbidding house.
not It was a dark, gloomy, forbidding, house.

All three modifiers— dark, gloomy, and forbidding—modify house.

Sometimes, what seems to be a modifier is actually part of the element being modified. Look at the following examples.

He is a tall, good‐looking, intelligent young man.

Young man, not just man, is the element being modified. Therefore, don't use a comma after intelligent.

They bought a beautiful, spacious summer home.

Summer home, not just home, is being modified. Don't use a comma after spacious.

To test whether you should use a comma before the last adjective in a series, see if it makes sense to reverse the order of the adjectives. If you can reverse them without changing the meaning or eliminating sense, then use commas between them. If you can't, don't.

It was a dark, gloomy, forbidding house.
It was a forbidding, dark, gloomy house. (no change in meaning)

In the previous example the order of the adjectives can change; therefore, use commas between them.

They bought a beautiful, spacious summer home.
They bought a summer, beautiful, spacious home. (does not make sense)

In the second sentence, changing the order of the adjectives makes the sentence nonsensical. Therefore, you would not use a comma between spacious and summer.

Commas with quotation marks

Commas always go inside quotation marks, whether or not they are part of the quotation.

He called her “ the worst boss in the world,” and he sent a series of threatening letters.
“I can't believe you ate the entire watermelon,” she said.

Miscellaneous uses of the comma

There are some special situations in which commas are necessary. Use commas in the following instances:

  • To present quotations, with he said, she muttered, etc.

He said, “Let's go.”

“Wait a while,” she said, “and I will.”

  • Between items in dates and addresses (except between state and zip code)

1328 Sailor Road, Santa Paula, CA 93060

December 10, 1962

  • Between cities and counties, cities and states, and states and countries

Boise, Idaho

  • To set off items in dates and addresses within sentences

December 10, 1962, was her birthday.

He lived at 23 Park Street, Boise, Idaho, until he left for Chiapas, Mexico.

  • In numbers of more than four digits

50,000

293,456,678

  • After salutations and closings in letters

Dear Rachel,

Sincerely,

  • To enclose a title or degree

Jeff Nelson, D.D.S., spoke at the dinner.