Basic Rules for Using Commas

The following eight rules will be useful for the type of essays typically required in college English classes, but are useful for any type of writing. Following each rule are example sentences.

1. Commas are used before coordinating conjunctions that link independent clauses.

Check to see that each independent clause has both a subjectand a verb.

1.1  The sky was dark, and the air was still

1.2  Robert entered the race, but he did not win.

1.4  My sister went home and fell asleep. (No comma needed; one subjectperforms two actions.)

2. Commas are used after a dependent clause or introductory phrase that precedes an independent clause.

2.1  For example, fructose is fruit sugar that is metabolized as a blood sugar.

2.2  If the man is good, he will be rewarded.

2.3  After he heard the concert, he realized the entire class should have heard it. 

3. Commas are used to set off phrases and clauses that merely add additional information.

The words on each side of the commas must make a complete clause or sentence.

3.1  Robert Frost, who wrote "The Road Not Taken" was an American poet.

3.2  That boy is, I believe, a dependable fellow.

3.3  Flashlight fish, equipped with glowing spots that blink, use these lights to attract prey.

4. Commas are used to separate each item in a series.

Each item in a series can be a single word, or an entire phrase. Usually the word "and" is used before the last item in the series, but that depends on the sentence (see 4.3).

4.1  The farmer sold corn, hay, oats, potatoes, and wheat.

4.2  They came from the east, from the west, from the north, and from the south.

4.3  The inadequacies of our relationship, the forced affection, the things never said, the weak and unmade gestures, were all no doubt responsible for the desire to find out what went wrong between us.

4.4  It is geometry of the pitted, pocked, and broken up, the twisted, tangled, and intertwined. (--James Gleick)

5. Commas are used between adjectives that modify the same noun.

Usually this rule works if the word "and" can be placed between the adjectives without changing the meaning of the sentence. Do not place a comma between the final adjective and the word it modifies.

5.1  I arrived at my school on a sunlit, windy day.

5.2  The show included the work of a small, innovative group of artists.

5.3  What I want is a big coconut creampie and a glass of milk. (Placing "and" between the adjectives makes the sentence sound awkward.)

6. Commas are used to separate the speaker from the quote.

Note that the comma is inside the quotation mark when the quote is split, as in sentence 6.2.

6.1  The woman said, "Wait for me."

6.2  "People are started to use cable anyway," he said, "so why not move our product there too?"

7. Commas are used to prevent misreading the sentence.

7.1  Ever since, Frank has been a better boy. (Without the comma: "Ever since Frank has been…")

7.2  She slipped her shoes on quickly, deciding to go out. (Without the comma: "…quickly deciding to go out.")

7.3  If he enjoys driving, a car would make a good gift. (Without the comma: "If he enjoys driving a car…")

8. Commas are used to separate dates, addresses, and numbers to make them easier to read.

8.1  They were married on Saturday, June 26, 1995.

8.2  The town has a population of 172, 500.

8.3  The party was held at 429 Mickmaw Street, San Diego, California.