Commas (,)

The comma serves two main purposes: First and most important, it separates elements, such as items in a series.

Second, just as an apostrophe indicates missing letters, so a comma indicates a missing word or words: The bread was fresh; the salad, crisp; the terrine, divine.

“To my parents, Ayn Rand and God.”

That classic example—purportedly from a book’s actual dedication page—shows the confusion that can ensue when a comma is omitted before and. Including the comma before and (called a serial comma) clears up the ambiguity.

Follow these rules when writing a series of items:

• In a series consisting of three or more elements, separate the elements with commas. When a conjunction (like and or or) joins the last two elements in a series, include a comma before the conjunction.

Examples
Confirm your name, birth date, and gender.
You may buy our gizmos online, in a store, or by mail.

• When using an ampersand in place of and in a series (acceptable only in company names and when space is severely limited), do not insert a comma before it. The combination of comma and ampersand creates visual clutter.

Example
Before
He went to Dewey, Cheatem, & Howe for financial advice.
After
He went to Dewey, Cheatem & Howe for financial advice.

• Use a comma to separate a series of adjectives equal in rank. (Here, the comma represents the missing word and.)

Exception
Do not insert a comma after a “superposed” adjective, one that modifies the whole noun phrase following it. (A noun phrase is one or more words functioning as a single noun. A noun phrase can be quite long; for example, aluminum fishing boat and handmade white linen tablecloth can be considered noun phrases.)

Examples
He was a happy, well-adjusted boy.
Other than the cold, hard rolls and the dry, flavorless salmon, Marco enjoyed his meal.
He put brand-new snow tires on the car.
His shiny aluminum fishing boat stood out among the rusty old trawlers.
I bought an expensive handmade white linen tablecloth.
She lives in a red brick, green-gabled Edwardian-era manse.

Use a comma, or a pair of commas if needed, to indicate that a word, phrase, or clause is not essential to the meaning of the noun it modifies.

Example
Beethoven composed only one opera, Fidelio, which he revised several times.

A modifying word or series of words set off by commas signals the reader that it can be removed without changing the sentence’s meaning. If commas are incorrectly inserted, they can lead to a wrong or improbable conclusion.

Examples
Before
I went with my friend, Sally, to see the latest Coen brothers film. (Sadly, I have only one friend; her name is Sally.)
After
I went with my friend Sally to see the latest Coen brothers film. (I have many friends; the one I’m talking about is Sally.)

Before
Editors, who earn six figures, are well-respected. (All editors earn six figures and are well-respected to boot.)
After
Editors who earn six figures are well-respected. (Those editors who earn six figures are well-respected; the others might not be.)

A comma customarily sets off introductory words, phrases, and clauses. Of course, some exceptions apply.

In general, use a comma after an introductory phrase that is four or more words long.

Examples
In 1492 Columbus sailed the ocean blue.
At the library you can find a book about him.
After paying the rent, she has just enough money to buy food.
To express her true nature, the chicken crossed the road.
After great pain and months of physical therapy, Joe could walk again.

Exceptions:

• A comma is generally advisable when a sentence starts with a transitional word or phrase (an adverbial conjunction) such as however (but not but), nevertheless, well, yes, no, meanwhile, furthermore, still, also, hence, consequently, therefore, moreover, fortunately, unfortunately, finally, what’s more, in fact, and after all.

Examples
Well, this is a fine kettle of fish!
No, I don’t want to eat any more pie.
Furthermore, I’ve decided to give up sweets entirely.
However, I’ll take that piece of cheese off your hands.
But don’t give me any crackers!

• Use a comma with a shorter introductory phrase if the lack of a comma could lead to a temporary misreading.

Example
Before
After eating the baby started to burp noisily.
After
After eating, the baby started to burp noisily.

• Use a comma to set off an introductory dependent clause. This is a clause that cannot stand alone because it begins with a subordinating conjunction such as after, before, because, even if, given, how, if, then, unless, or while. (Remember that a clause has both a subject and a verb.)

Examples
If it bleeds, it leads.
Because I could not stop for Seth, he kindly stopped for me.

Although introductory elements often require commas, the same elements may not need to be set off by commas at the end of a sentence. However, listen to the rhythm of the sentence. If you pause at the beginning of the element, then set it off with a comma. If you do not pause, do not insert a comma.

Examples
It leads if it bleeds.
The chicken crossed the road to express her true nature.
Joe could walk again, after great pain and months of physical therapy.
Joe could walk again only after great pain and months of physical therapy.

To set off a parenthetical element—whether a word, a phrase, or a clause—use a pair of commas when you intend only a slight interruption. Otherwise use a pair of em dashes or parentheses.

Examples
The chicken, regrettably, crossed the road.
The rooster was, to say the least, quite saddened.
The pig, I heard, was also unhappy.
The cat—which hated the chicken’s slow-witted squawking—looked forward to sampling the truck-spatchcocked bird.

Use a comma to set off a name, a title, or another word or phrase when addressing someone.

Examples
Dear customer,
Friends, Romans, countrymen, lend me your ears.
Madam President, I move to adjourn.

The coordinating conjunctions for, and, nor, but, or, yet, and so can link two independent clauses (clauses that can stand alone as sentences).

Follow these rules when punctuating sentences with these conjunctions:

• Use a comma before the conjunction.

Examples
Roscoe dropped the saliva-covered ball at her feet, but he was then distracted by a squirrel.
Hidden zones appear at level 12, and a brightly lit fountain then sprays the screen with gems.

• Don’t use a comma to separate independent clauses if they are not joined by a conjunction—that’s called a comma splice. Instead, use a semicolon, add a conjunction, or if necessary, rewrite the sentence.

Example
Before
Most of us are just out of college, we can’t afford a whole corporate wardrobe. (Comma splice)
After
Most of us are just out of college; we can’t afford a whole corporate wardrobe. (Semicolon)
Most of us are just out of college, so we can’t afford a whole corporate wardrobe. (Conjunction)

• Don’t use a comma before every conjunction in a sentence. Often a conjunction joins two verb phrases that share a subject. In such a case, either delete the comma or insert a second subject.

Example
Before
The chicken crossed the road, but soon regretted her decision. (One subject: “chicken.” Two verbs: “crossed” and “regretted.” The verb phrase “soon regretted her decision” does not have its own subject.)
After
The chicken crossed the road but soon regretted her decision. (Comma deleted.)
The chicken crossed the road, but she soon regretted her decision. (“She” inserted so that the verb phrase “soon regretted her decision” now has its own subject.)

• Sometimes, however, a comma helps the reader understand a complex sentence.

Example
The chicken strutted across the road thinking that she cut quite a fashionable figure, and considered herself the most favored creature of the barnyard.

Follow these guidelines for punctuating a quotation with commas:

• Use a comma to introduce a complete one-sentence quote.

Example
The young man said, “I’m here to watch the next Triple Crown winner.”

• Don’t use a comma before an indirect or partial quote.

Example
The young man said he was there “to watch the next Triple Crown winner.”

• Use a comma at the end of a quote that is followed by an attribution such as “he said.”

Example
“I’m here to watch the next Triple Crown winner,” the young man said.

• Don’t use a comma at the end of a quote that is followed by an attribution if the quoted statement ends with a question mark or an exclamation point.

Example
“Why are you here?” the reporter asked the young man.

In running text, use a comma to set off parts of an address or a place name.

Examples
The spy met her controller in the basement of 100 Lexington Ave., Columbus, Ohio, on the first Monday of each month.
The company opened a branch in Edmonton, Alberta.
I would like to visit my uncle in Kolkata, India, one day.

Set off the year with commas when it follows the month and date. Set off the month and date when they follow the day of the week.

Examples
Both Thomas Jefferson and John Adams died on July 4, 1826, the 50th anniversary of the signing of the Declaration of Independence.
He was born on Monday, December 31, just in time to give his parents a tax break.

Do not insert a comma between the month and the year if no date is included.

Example
He was born in December 2009.

Use commas for numbers greater than 999 expressed in numerals: 30,000 pounds. For more examples and some exceptions to this rule, see “The Basics.”