Comma Use

At first glance, commas can be intimidating.  They are common, have many rules for use, and play an essential role in writing.  Commas clarify parts of phrases and sentences that might otherwise be difficult to understand. By explaining how the separate parts of the sentence are related, commas fulfill a crucial function for the reader. Their uses, while many, can be learned fairly quickly. Commas are generally used in the following situations:

1. Introductory Phrases—Use a comma following an introductory phrase that has four or more words. These phrases can be located preceding the main subject and verb in a sentence. In the examples below, the introductory phrases are underlined.

Once upon a time, there was a little boy named Hansel who had a sister named Gretel.

In her latest book, Linda Flower writes about reading and writing in everyday life.


2. Subordinate Clauses at the Start of a Sentence—A subordinate clause at the beginning of a sentence should be followed by a comma to distinguish it from the main/independent clause. In the examples below, the subordinate clauses are underlined.

When I was a little girl, I liked to play with blocks.

Because I am tall, people often ask if I play basketball.

Some commonly used subordinating conjunctions are: Although, As, Because, If, Since, Though, While, When.


3. Items in a Series—When listing three or more items in a series, use commas to distinguish among items. For example:

For breakfast I had toast with jam, scrambled eggs, and a cup of coffee.

With my pencil, scrap paper, and calculator in hand, I entered the classroom with confidence in my ability to ace the math exam.


4. Coordinating Conjunctions—To combine two independent clauses (full sentences), use coordinating conjunctions preceded by a comma. In the example below, the coordinating conjunction is underlined.

She was my best friend, and she was my sister.

There are only seven coordinating conjunctions, and they can be remembered using the mneumonic device FANBOYS:

For And Nor But Or Yet So

5. Conjunctive Adverbs—To join two independent clauses (full sentences), one can also use conjunctive adverbs preceded by a semi-colon and followed by a comma. In the example below, the conjunctive adverb is underlined. Other commonly used conjunctive adverbs are moreover, for instance, therefore, nevertheless.

I love horses; however, I was very frightened the first time I rode one.

6. Appositives and Embedded Clauses—When a clause that is not necessary to the meaning of the sentence is interjected into a sentence, set off the phrase with commas. Extra information needs extra punctuation. In the examples below, the appositives/embedded clauses are underlined.

          Samantha, my younger cousin, worked as a lifeguard last summer.

I often visit Indianapolis, where my grandmother recently moved, to visit family and friends.


7. Dates and Addresses—Dates and addresses are offset by commas when they occur in prose as a convention of standard, edited American English. For example:

            Abraham Lincoln was born on February 12, 1809, in Hodgenville, Kentucky.

            My parents were married on June 18, 1983.

8. To Indicate Clarity—Following the aforementioned comma rules is important to keeping the meaning of your sentences and ideas clear for readers. Compare the following:

            “Let’s eat, Grandma!” vs. “Let’s eat Grandma!”

9. In Dialogue—when writing dialogue, you can separate what is being said from the description of the action. For example:

            “Hi, Joe,” I said as I walked into the room where my friend sat reading a book.

Note:  If any other punctuation is used in dialogue quotations, that punctuation takes the place of the comma. For example:

“Use the fire extinguisher to put that out!” I yelled at Joe.


Common Comma Errors

  • Subordinating conjunctions don’t need to be set off by commas when the subordinate/dependent clause follows the independent clause (compare with section 2 above). For example:

            Incorrect: I liked to play with blocks, when I was a little girl.

            Correct: I liked to play with blocks when I was a little girl.

  • A comma cannot be used to join two (or more) independent clauses together in a single sentence. This situation is called a comma splice. For example:

            Incorrect: I ran a marathon, I finished with my best time ever!

            Correct: I ran a marathon, and I finished with my best time ever!

Note: You have multiple options for fixing a comma splice:

  1. Replace the comma with a semi-colon.
  2. Divide the comma-spliced sentence into two smaller sentences.
  3. Insert a coordinating conjunction after the comma (see section 4 above).