Uses of the Comma

Joining independent clauses

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

• Lenin never answered these charges, but soon afterward he was compelled 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.

Remember that when you do use a comma between independent clauses, it must be accompanied by one of the coordinating conjunctions. If it isn't, you create a run-on sentence.

• 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.

With today's trend towards light punctuation, you may omit the comma if the subordinate clause is short, and if there is no possibility for confusion.

• When she arrived we stopped gossiping.

• After I was sixteen I was allowed to stay out until midnight.

Be sure that omitting a comma will not lead your reader to a momentary misunderstanding. Look at the example below.

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

• When we are cooking, children cannot come into the kitchen.(yes)

Without a comma, your reader may suspect you of cannibalism.

After introductory phrases

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

If an introductory phrase is more than a few words, it's a good idea to follow it with a comma. And always use a comma if there is any possibility of misunderstanding a 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 so many performances of the symphony, this one was spirited and lively.

• Before eating, Jack always runs on the beach.

Note that the introductory phrase in the last example, although short, would lead to a momentary 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 would 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.

• For some unknown reason the car wouldn't start.

The best way to decide whether to use a comma is to read your sentence aloud and see whether you pause distinctly after the introductory phrase. Use a comma if you do.

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

• For example, you shouldn't use the 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 is strong at research, for example, might be assigned to the library.

Know what your intention is. If you want the reader to pause, use the commas. If you don't, omit them. Look at the following two examples.

• The committee, therefore, agreed to hear the students.

• The committee therefore agreed to hear the students.

Both sentences are correct. In the second sentence the expression would be read as part of the flow of the sentence, not as an interrupter.

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

• Friends, I am here to ask for your support.

• I tell you, Mr. Smith, 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.

Dashes and parentheses can also be used to set off some kinds of interrupting elements, but 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. In the simplest terms, 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, however, the information who arrived yesterday is not necessary to the sentence. It does not separate the women from all other women. The clause adds information, but the information isn't essential to our knowing which women are being discussed. It is you, as writer, who must decide which kind of information you intend to give.

Commas make all the difference in meaning here. Restrictive (or essential) elements shouldn't 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 exactly which workers were replaced.

In the following sentence, the phrase who are over fifty is essential in limiting the subject men and therefore should not be enclosed in commas. The second sentence means that all men are over fifty, which is absurd.

• Men who are over fifty have difficulty finding a new job.

• not  Men, who are over fifty, 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 (added information).

• My brother, who is thirteen, watches television more than he reads. (added 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. (added information)

• Cats who are fussy eaters are a trial to their owners. (essential)

• My brother, swimming in the ocean, saw a shark. (added information)

• People swimming in the ocean should watch for sharks. (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.

• Patricia Mack, my old friend from college, became a successful writer.

Sometimes, however, an appositive is essential because it limits the subject. It must not, therefore, 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 suggest that Shakespeare wrote only one play. Obviously, the appositive Hamlet is restrictive; it limits the subject play.

Between items in a series

Use commas to separate items in a series. Although some editors feel that it is acceptable to omit the final comma in a series—journalists and business writers frequently do—it is safer not to.

• He bought a dishwasher, microwave, refrigerator, and washer from the outlet.

• Her play is filled with coincidences, false anticipations, and nonresponsive dialogue.

Omitting a final comma may create ambiguity, and since you should be consistent throughout a piece of writing, why not consistently use the final comma and avoid possible problems?

• Hair, clothing and jewelry all send messages to a prospective employer. (acceptable)

• Hair, clothing, and jewelry all send messages to a prospective employer. (better)

• She told us about the subway, the elevators at Bloomingdale's and the Metropolitan Museum of Art. (ambiguous: the elevators at both Bloomingdale's and the Metropolitan Museum or just at Bloomingdale's?)

• She told us about the subway, the elevators at Bloomingdale's, and the Metropolitan Museum of Art. (better)

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.

In this example, all three modifiers— dark, gloomy, and forbidding—modify house.

Sometimes, however, 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)

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)

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

Commas with quotation marks

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

• He called her “that fiend from Hell,” 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 where you should use commas. For example, commas are used 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 Say Road, Santa Paula, CA 93060

  • December 10, 1902

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

  • Boise, Idaho

• To set off items in dates and addresses within sentences

  • December 10, 1902, is his 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 Judith,

  • Yours truly,

• To enclose a title or degree

  • Jeff Nelson, LL.D., spoke at the dinner.