Writing Resources: Commas

Use a comma to set apart an introductory word or phrase.

When a sentence doesn't begin with the subject but has instead an introductory word or phrase, a comma must separate the introduction from the rest of the sentence.

Despite his best efforts, the hero failed.

The comma goes between the introduction and the subject and must not separate the subject from the verb. Introductory elements often consist of prepositional phrases, subordinating conjunctions, participial phrases, or conjunctive adverbs. Phrases that begin with the following words often require a comma if they begin a sentence (this list is not exhaustive):

according to

besides

instead of

until

after

between

when

although

despite

once

whenever

due to

rather than

where

even though

since

wherever

because

except for

though

while

because of

toward

with

before

in order to

unless

without

The following words usually have a comma immediately after them when they begin a sentence. Many adverbs that end in -ly and transitions at the beginning of a sentence need to be followed by a comma, too. Finally, a comma must follow an introductory participial phrase. A participle is a verb ending in -ing that acts as an adjective.

additionally	first (second, etc.)	likewise	otherwise
after all	furthermore	meanwhile	presently
afterward	however	namely	regardless
again	in other words	naturally	similarly
also	in the end	nevertheless	still
anyway	indeed	next	therefore
consequently	instead	of course	thus
finally	last	on the contrary	undoubtedly

Participles are often used with the above introductory words, but they can also stand alone.

Sitting across the table from me, he asked a question.

When a verb immediately follows an introductory element, however, don't use a comma. Such a case occurs if the introduction is serving as the subject of the sentence or if the sentence uses inverted word order. A comma is sometimes optional after certain prepositional phrases, too. You can tell if you need a comma by whether you pause while reading the introductory element aloud. However, if you're in doubt, use a comma.

Running the race is the fulfillment of his dream.

After the race came the victory lap.

At night the stars come out.

Use a comma to join a dependent clause to an independent clause when the dependent clause is first.

A dependent clause is a clause with a subject and verb that can't stand alone because of its first word (often one of the words from the first list above). If you were to say a dependent clause out loud, people would expect you to say more:

Because we jumped in the pool.

When a dependent clause begins a sentence, a comma must follow it:

Because we jumped in the pool, we were soaked.

Use a comma wiith a conjunction to join two independent clauses.

When you have two complete sentences--with two subjects and two verbs--you can't use only a comma to separate them. (When you do, it's called a comma splice.) You have to use a semicolon or a comma with a conjunction to join them, or you can make them two sentences. When the two sentences are short and closely related, however, you can use only a comma between them. When in doubt, use a semicolon or a comma and conjunction.

He's very quiet, no one pays much attention to him.

He's very quiet, so no one pays much attention to him.

He's very quiet; no one pays much attention to him.

Use a comma to set apart nonrestrictive material.

Restrictive material restricts the meaning of the preceding noun:

Children who play with matches should be punished.

Here the statement refers only to children who play with matches. Compare:

Children, who play with matches, should be punished.

This statement refers to all children as children who play with matches, so it isn't restrictive. The sentence would not change in meaning if you omitted the material enclosed by the commas, which is the test as to whether something is nonrestrictive. If it would mean the same thing without a certain phrase, then you must enclose the phrase in commas. If the material is necessary for proper understanding, as in the first sentence, then you shouldn't use commas. Often students use commas to set apart material that should be restrictive, which leads to confusion. Be aware of this. Finally, that is better for restrictive material and which is better for nonrestrictive material.

The plant that thrives is fortunate.

This project, which took her weeks to complete, is the best in the class.

Use a comma to set apart an appositive or an interrupting word or phrase.

An appositive is a word or phrase that repeats the preceding noun in different words, generally to amplify meaning. Anything that interrupts the flow of the sentence and that the sentence could do without should have a comma on both sides.

The cheetah, the fastest land animal, can reach speeds of seventy miles per hour.

I mean, wow, who would have guessed?

Use a comma to separate items in a sequence.

When you list three or more items, it's best to put a comma after every item except the last, including the one that precedes the and or the or. This way you can avoid possible confusion.

Use a comma to separate adjectives or adverbs that modify the same word.

Modifiers that modify the same word need commas separating them if there are two or more and if you could sensibly put the word and between them.

It's a tall, impressive building.

The unusual cardboard box was strangely shaped.

Use a comma to introduce some quotations.

When there is a direct speaker, use a comma to introduce direct quotations. A colon is used for other quotations and citations. However, a quotation can also be its own sentence or lie unpunctuated within a sentence.

The angry girl shouted to her younger brother, "Stay out of my room!"

"Man does not live on bread alone, but on every word that comes from the mouth of God." This simple statement helps put things in perspective.

Crevecoeur's idea of a "pleasing uniformity of decent competence" is key to understanding how he views America.

Use a comma in dates, addresses, titles, academic degrees, and long numbers.

After the day and, in a sentence, the year:

On November 27, 1975, my big brother was born.

After each part of an address:

She's at 698 Norfolk Street, Holliston, Massachusetts, where she works.

To indicate a person's title or degree:

Julius Lombard, Ph.D., is my professor.

After every three digits in a number:

5,980,672