Handbook: Writing Problems and How to Correct Them

12 Commas

Commas

A comma (,) is used to separate parts of a sentence from one another. Commas, when used correctly, make your sentences clear and help readers understand your meaning.

12a Use a comma before a coordinating word (and, but, for, nor, or, so, yet) that joins two independent clauses

12b Use a comma to separate three or more items in a series

A series is a list of three or more items—words, phrases, or clauses.

Some writers omit the comma before the coordinating conjunction (such as and, or) in a brief series when using a casual or journalistic style. Occasionally this omission can create confusion, so it is better to include the final comma.

CONFUSING	She insured her valuable heirlooms, watches and jewelry.
	Do her heirlooms consist entirely of watches and jewelry, or did she insure three kinds of items?
CLEAR	She insured her valuable heirlooms, watches, and jewelry.

A comma is not used after the last item in a series.

(See also 13c on when to use semicolons to separate items in a series.)

12c Use a comma to separate two or more adjectives that modify the same noun when they are not joined by a coordinating word

To be sure a comma is needed, try reversing the two adjectives. If the phrase still sounds correct when the adjectives are reversed, a comma is needed. If the phrase sounds wrong, a comma is not needed.

The phrase open, airy atrium sounds right, so a comma is needed.

The phrase red, bright uniforms sounds wrong because bright modifies red uniforms in the original sentence. A comma is not needed.

12d Use a comma to separate introductory words, phrases, and clauses from the rest of a sentence

INTRODUCTORY WORD	Above, the sky was a mass of clouds.
	Without the comma, this sentence would be confusing.
INTRODUCTORY PHRASE	At the start of the project, the researchers were optimistic.
INTRODUCTORY CLAUSE	When alcohol was outlawed, many solid citizens broke the law.

Exception: A comma is not needed after a single word or short phrase or clause when there is no possibility of confusion.

12e Use a comma to set off a nonrestrictive word group from the rest of the sentence

A nonrestrictive word group describes or modifies a word or phrase in a sentence, but it does not change the meaning of the word or phrase. To decide whether a comma is needed, read the sentence without the word group. If the basic meaning is unchanged, a comma is needed.

The meaning of fruitcake is not changed by the relative clause which is a traditional holiday dessert, so the word group is nonrestrictive and a comma is needed.

The phrase wearing a tutu identifies which child delights in ballet lessons, so the word group is restrictive—necessary to explain what the word it modifies means—and a comma is not needed.

12f Use a comma to set off parenthetical expressions

A parenthetical expression provides extra information. It can also be a transitional word or phrase (however, for example, at the beginning) that is not essential to the meaning of the sentence.

12g Use commas with dates, addresses, titles, and numbers

When you give only a month and year, a comma is not needed.

Place a comma after the date when it appears before the end of the sentence.

When you give an address within a sentence, do not place a comma between the state and the ZIP code.

Separate a name from a title with a comma.

Use commas in numbers that have more than four digits.

In a number with four digits, the comma is optional: 1500 or 1,500.

12h Use a comma to separate a direct quotation from the words that explain it

Place the comma before the closing quotation mark.

(See also 15b and 15e.)

12i Use commas to set off the name of someone directly addressed, to set off an echo question, and with a “not” phrase

DIRECT ADDRESS	“James, answer the question concisely.” “Bail has not been granted, your honor.”
ECHO QUESTION	More development will require a more expensive infrastructure, won’t it?
“NOT” PHRASE	Labor Day, not the autumnal equinox, marks the end of summer for most Americans.