Reading Writing Center | Microlab 3

Microlab 3 - Comma Usage

Placed correctly, commas help create a clear meaning. Placed incorrectly, commas can distort meaning and confuse readers. Good writers learn when—and when not—to use commas for the sake of clarity in their writing. This microlab will help you:

  • Understand the many uses of a comma
  • Recognize comma errors
  • Repair comma errors

Review of Commas

The comma is the punctuation mark that has the greatest variety of uses in English. This review will help explain and give examples of the many uses of this important punctuation mark. Commas serve two basic functions in a sentence. Some commas separate a word, phrase, or clause from the rest of the sentence. Other commas enclose a word, phrase, or clause that is not essential to the central meaning of a sentence.

Commas that Separate

I. Between independent clauses [two complete sentences]:

Use commas to separate independent clauses joined by a coordinating conjunction (such as “and,” “but,” “or ”etc.), or correlative conjunctions (“either...or,” “neither…nor,” etc.). The comma goes before the conjunction:

Correct:  The clown’s performance was familiar, yet it always brought laughs. 
Incorrect: The clown’s performance was familiar yet it always brought laughs. 

Notice how each of the independent clauses below are separated by a comma:

Correct:  She watched the pendulum swing back and forth, but it failed to hypnotize her.
Correct:  Either Ho Kwong will drive us to town, or we will take the bus.

Sometimes the comma between two independent clauses is essential to prevent misreading:

Correct: The animals quickly got used to the fenced yard, and the goat seemed like a pet. 
Incorrect: The animals quickly got used to the fenced yard and the goat seemed like a pet. 

Without the comma, the reader might read the meaning of the sentence differently. Did the animals get used to the fenced yard and the goat, or did the animals only get used to the fenced yard? You can learn more about using commas with independent clauses in any grammar book: see “independent clauses” and “coordinating conjunctions.”

II. Introductory words/phrases:

Use a comma to separate introductory words or phrases (such as also, however, in addition to, etc.) from the rest of the sentence. Put the comma after anything that comes before the subject of the sentence:

Correct:  Before leaving, Paris Hilton hosted an unforgettable party. 
Incorrect:  Before leaving Paris Hilton hosted an unforgettable party. 

Without the comma, the reader might think that someone named Hilton put on a party before leaving Paris. Notice how the commas separate each of the introductory words in the sentences below:

In addition to homework, students often have to work part-time. 
While the band played, six dancers entertained the crowd. 
Frustrated, the researcher tossed her notes out of the window. 
However, she didn’t seem to fully appreciate what he was doing for her.

III. Lists:

When three or more items occur in a list (called a “series”), commas separate each item. Be sure to place a comma before the “and” that precedes the last item in the series!!!

Correct:  There were many Thai treats behind the glass, including khanom chan, thong ek, 
and krachao sida.  
Correct:  I went to the store to buy flour, eggs, milk, and cookies.
Incorrect:  My dad’s job includes market research, report writing and research and 

With a series of phrases, three or more phrases in a series are separated by commas:

Correct:  The catalog described tools for the shop, furniture for the home, and items for 
the office.

With a series of clauses, three or more clauses in a series are also separated by commas:

Correct:  Fans cheered, flags waved, and fireworks exploded.

IV. Dates, addresses, titles:

Use commas to separate parts of dates, items in addresses, and titles that follow names. Dates: Commas separate the day, the date of the month, and the year:

Correct:  She chose Tuesday, December 19, 2006 as her wedding day.

Addresses: Commas separate the name, street address, city name, and state name:

Correct:  Last year, I worked for ATC Enterprises, 208 Gilmore Street, Baltimore, Maryland 

Titles: Commas separate titles and degrees that follow names:

Correct:  Rita Ortiz, Ph.D., invited the audience to ask questions.

**If the title precedes the name, no comma is used:

Correct:  Vice President Tony Frangillo read the startling report.

V. Quotations:

Use commas to separate expressions like “he said” and “she answered” from a direct quotation. A comma that follows a direct quotation belongs inside the quotation marks:

Correct:  “Leave the rest,” he said, “to the police department.”
Correct:  She asked, “Which door is the exit?”

*Notice that no comma is used when a direct quotation ends with its own punctuation.

Correct:  “Sound the alarm!” he shouted.

VI. Between two adjectives:

When you have two different adjectives modifying the same noun without a conjunction, you need to have a comma between them. This can save a lot of confusion! Which sentence is which? Look at that big hot dog! or Look at that big, hot dog!


VII. Nonrestrictive phrases:

Use commas to enclose groups of words that provide additional information not essential to the basic meaning of the sentence: Basic sentence: The oil painting bore a famous artist’s signature. Additional information: stored in the attic for years Combined (with commas): The oil painting, stored in the attic for years, bore a famous artist’s signature. The portion of this sentence enclosed by commas is called a nonrestrictive phrase. A nonrestrictive phrase gives additional information that does not affect the basic meaning of the sentence. In fact, the nonrestrictive phrase could be removed, and the sentence would still make sense. Nonrestrictive phrases may often times be set off by parentheses or dashes. This may help the clarity if there is a comma within the nonrestrictive phrase (see Microlab 6—Parentheses and Dashes):

Correct:  The plants—which had not been cared for—sat wilting in the corner.
Correct:  The twins (who wore identical shorts, blouses, and even socks) caught many long 
stares as they walked through the store.

Nonrestrictive phrases often begin with “which”:

Correct:  The assignment, which I finished yesterday, was not difficult.

VIII. Restrictive phrases:

A group of words that provides descriptive or identifying information essential to the basic meaning of the sentence should not be enclosed by commas and is called a restrictive phrase:

Correct:  Students who keep up with reading assignments do well on finals.

The underlined portion of this sentence tells us which students do well on finals and is therefore essential to the meaning of the sentence. (Notice how the meaning changes when the underlined words are omitted from the sentence.)

Correct:  The car that I bought last year continues to run well.

The phrase “that I bought last year” tells us which car runs well. These identifying groups of words are called restrictive phrases. They limit or restrict the meaning of the sentence by providing identifying information:

Correct:  The boat that comes in first will win a prize.

IX. Nonessential words:

Use a pair of commas to enclose nonessential words that interrupt the flow of the sentence:

Correct:  None of the trees, however, suffered damage.
Correct:  Her best dancing, in fact, came early in her career. 

X. Names:

Use commas to enclose the names of people addressed directly by the sentence: George is the person being spoken about in this sentence, so his name is set off by commas:

Correct:  My favorite friend, George, loves swimming in non-polluted lakes.

In this sentence, Sally is being addressed directly, so her name is set off by commas:

Correct:  Regular practice, Sally, brings steady improvement.

A Handy Reminder:

When you are unsure if a comma should be used, decide whether the comma will make the meaning of the sentence clearer. If so, include the comma. If not, leave the comma out!

Key Points to Remember:

  1. Commas are used to separate parts of a sentence:
    • Clauses joined by a coordinating conjunction
    • Introductory words or phrases
    • Items, phrases, or clauses in a series
    • Parts of dates, addresses, and titles that follow a name
    • Words like “he said” in direct quotation
    • Two adjectives modifying the same noun
  2. Commas are used to enclose parts of a sentence:
    • Phrases or clauses that supply additional, nonessential information
    • Nonessential words that interrupt the sentence
    • The name of a person addressed directly