4.2 Commas


This section of Ch. 4 will cover the following topics:

  • basic comma rules
  • run-on sentences/comma splices

Commas are the most frequently used punctuation mark and also the most common punctuation error.

Like other punctuation, the job of a comma is to help the reader understand how something is said. The message commas send is this: pause here, just for a second.

Try to read the following sentence:

I have three pigs four cats with six toes a gerbil named Hammy an old spotted cow who still gives milk and an Irish wolfhound named Vanessa.

You don’t know where to pause; you struggle to break the information into understandable chunks. Now read this:

I have three pigs, four cats with six toes, a gerbil named Hammy, an old spotted cow who still gives milk, and an Irish wolfhound named Vanessa.

Commas help us translate words on the page into meaning.

Commas used incorrectly can make the reader’s job harder. It’s the writer’s responsibility to use commas correctly, not the reader’s responsibility to figure out what the writer means.

Basic Comma Rules

  • Commas have two jobs: they either separate or they enclose. Remember that, and you are halfway there.
  • There are seven main rules for comma use. Understanding these seven rules will eliminate nearly all of the comma errors in your writing.

Commas That Separate

Rule 1: Use a comma to separate joined by the known as “fanboys”: for, and, nor, but, or, yet, so.

For example:

  • We brought chips to the party, and our neighbors were appreciative. (“We brought chips to the party” is an independent clause–it has a subject, a verb, and a complete thought. “our neighbors were appreciative” is also an independent clause. The two independent clauses are joined by the conjunction “and,” so we put a comma in front of “and.”)
  • My geology textbook is expensive, so I’ll find a used copy. (“My geology textbook is expensive” is an independent clause. “I’ll find a used copy” is also an independent clause. The two independent clauses are joined by the conjunction “so.” Put a comma in front of “so.”)

Caution: Be sure the conjunction connects two independent clauses, not just two words or two phrases or even two dependent clauses. For example:

My dog curled up on the sofa and waited for dinner. (“and” joins the verbs “curled” and “waited.” The phrase “waited for dinner” is not an independent clause.  No comma before “and.”)

This rule clarifies a term you may have heard: comma splice. If we put a comma between independent clauses that are NOT joined by “fanboys,” that is called a comma splice. The comma is splicing, or cutting, the sentence into two parts. A comma splice is a comma error.


This is the most complicated comma rule, so keep working with it.

This is a :

Dogs are people’s best friends, people are a cat’s best friend.

To fix the error, add one of the “fanboys”:

Dogs are people’s best friends, but people are a cat’s best friend.

Understanding how a comma splice works has the added benefit of explaining what a run-on sentence is. A run-on is two or more independent clauses connected improperly.  For example:

I love to eat ice cream I would eat it every day if I could.

That can be fixed by adding a comma and the conjunction “and” after “ice cream,” or by putting a period after “ice cream” and making it into two sentences.

Exercise 1

In your notebook, join the pairs below by adding a comma and a “fanboys” conjunction. You may need to play with the wording a bit to make the sentence read smoothly.

  1. John wanted a snack before bedtime. He ate some fruit.
  2. We could go camping for vacation. We could go to the beach for vacation.
  3. I want to get a better job. I want to finish college.
  4. I cannot move forward on this project. I cannot afford to stop on this project.
  5. The weather was clear yesterday. We decided to go on a picnic.

Rule 2: Use commas to separate items in a series, date, or address. This comma allows the reader to pause after each item and identify which words are included in a group.

For example:

  • We need to get flour, tomatoes, and cheese at the store. (Separate items in the list with commas. Note: Writers sometimes leave out the comma before “and” in a simple series when the meaning is clear, but including it is always correct. That kind of comma is called an “Oxford comma,” by the way.)
  • Mr. Schaeffer could see a wild, overgrown jungle in his neighbor’s yard.  (Use commas between a series of adjectives that modify a noun.)
  • My grandfather was born on August 13, 1897, in Alameda County. (In a date, put a comma between the day and the year. If the sentence continues on, put a comma after the year. When only the month and year are used, no comma is needed: He was born in August 1897.)
  • My best friend’s address is 2600 Trillium Avenue, Mill Creek, Washington 97202, and she visits me often. (Put a comma after the street and after the city, but not between the state and the zip code. If you continue the sentence after the address, add a comma after the address.)

Exercise 2

In your notebook, copy these sentences and add commas where necessary. If the sentence is correct, write “Correct.”

  1. The letter was postmarked May 4 2001 but I didn’t receive it until June.
  2. He visited Italy in July 2009.
  3. We looked at the dark dangerous sky and wondered if we would make it home safely.
  4. I recently moved to 4542 Larkspur Lane Hope Missouri 70832.
  5. Eric lives in Boston Massachusetts and uses public transportation.

Rule 3: Use a comma to separate an introductory word or from the main sentence.

For example:

  • Finally, he received an Oscar for his work in film. (introductory word)
  • During last season, our team won nearly every game. (introductory phrase)

Rule 4: Use a comma to separate a tag question, contrast, comment, or description from the end of the main sentence. (A “tag” is an afterthought.)

For example:

  • The age restriction goes into effect in March, doesn’t it? (tag question)
  • Students who earn high grades are those who study, not those who cheat. (tag contrast)
  • She said she would “consider my application,” whatever that means. (tag comment)
  • We spent a month in Italy, visiting family. (tag description)

Most prepositional phrases and dependent clauses at the end of sentences are not tags and do not require commas. For example:

The word “ruminate” means to think about something. (“about something” is a prepositional phrase, not a tag. No comma.)

Exercise 3

In your notebook, copy these sentences and add commas where necessary.

  1. In the blink of an eye the kids were ready to go to the movies.
  2. Confused he tried opening the box from the other end.
  3. I prefer ice cream to vegetables don’t you?
  4. Without a doubt green is my favorite color.
  5. The best dogs are loyal and sweet not just beautiful.

Commas That Enclose

Rule 5: Commas are used to enclose (placed before and after) the name of a person being spoken to in a sentence.

For example:

Did you know, Sophia, that you left your book in class?


When people start studying commas, they tend to insert them everywhere. Don’t put a comma in a sentence unless you can explain the rule for doing so.

Rule 6: Commas are used to enclose transitions or expressions that interrupt the flow of the sentence (such as “however,” “by the way,” “on the other hand,” and “I think”).

For example:

I know, by the way, that my paper is late.

I will try, therefore, to be on time in the future.

Sometimes interrupters flow smoothly so they don’t need commas:

Of course you made the right choice.

I think he checked to see if he had his books.

If you are unsure whether an expression is interrupting, say it aloud. You can hear the pause before and after “by the way” in the first sentence. But you can’t hear a pause after “I think” in the last sentence.  Remember that punctuation is just pointing out how we would say the words if they were spoken.

Rule 7: Use commas to enclose extra or unnecessary information in the middle of a sentence.

For example:

Max O’Keefe, who organized the event, will introduce the speakers. (“who organized the event” is extra information that could be removed but we would still understand who organized the event.)

But be sure the information is unnecessary:

The person who organized the event will introduce the speakers. (We don’t know which person without the phrase “who organized the event,” so that phrase is necessary. No commas.)

Exercise 4

In your notebook, copy these short paragraphs, inserting commas where necessary. At the end of each sentence, write the number of the rule you used.

  1. Our meeting is scheduled for Thursday March 20. Before that time we need to gather all our documents. To prepare for this meeting please print any e-mails faxes or documents referred to in your report.
  2. The leader of the group Garth kept checking their GPS location. Isabelle Raoul and Maggie carried the equipment. As a result no one noticed the darkening sky until the first drops of rain.
  3. Please have your application submitted by April 15 2020. In your cover letter include contact information the position you are applying for and two references. We will not be available for consultation after April 10 but you may contact the office before then.


  • Commas separate or enclose units in a sentence.
  • Never use a comma unless you are sure which rule you are following.


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