When To Use a Comma: With Examples

This article explains how and when to use a comma in your writing, including examples of what to do and avoid.

The comma is a punctuation mark that is small in form but mighty in function. Comma use can either befuddle a reader or make all the difference in how well the reader understands what you are writing.

What Is The Purpose Of a Comma?

Simply put, a comma helps a sentence make sense. Similar to how a person’s voice might pause or change in pitch when talking, a comma signals readers to a quick pause or shift in tone. You might also be wondering when to use so and neither.

When to use a Comma: the Rules

Many so-called English “rules” apply to comma usage, but rather than letting those rules overwhelm you, try to remember the simple thought that commas help clarify the meaning of your sentences. If you know what a complete sentence is, you are well on your way to understanding comma usage.

Use a Comma When Combining Two Independent Clauses With a Coordinating Conjunction

Essentially, you’re writing a compound sentence, or two sentences made into one sentence, joined by a coordinating conjunction.

Think of a coordinating conjunction as a word that joins two complete thoughts into one with equal emphasis on both parts of the sentence.

Coordinating conjunctions are these words:

• for
• and
• nor
• but
• or
• yet
• so

Notice the beginning letter of each word. Put together, the letters spell “fanboys,” a good way of remembering coordinating conjunctions.

Here are two examples of this rule:

      Emma walked to the store, and Brad walked the dog.

      Emma walked to the store, but Brad walked the dog.

Where would you place the comma in the following sentence?

      Charlie struggled with building a snowman so his friend Danny helped him.

Use a Comma When Joining Two Independent Clauses With a Conjunctive Adverb

This rule is similar to the rule above, except you’re using conjunctive adverbs to join the independent clauses.

A conjunctive adverb is defined as an adverb that joins two sentences together and usually appears near the middle of a sentence. Examples of conjunctive adverbs include:

• however
• nevertheless
• therefore
• consequently
• besides
• finally
• similarly
• meanwhile

Be sure to place a semicolon (;) before the conjunctive adverb and a comma after it. Here are a few examples:

Emma walked to the store; however, Brad walked the dog.

Emma walked to the store; meanwhile, Brad walked the dog.

Where would you place the semicolon and comma in the following sentence?

      Brad did not walk the dog consequently he did not get to go to the movies with his friends.

Use a Comma To Join a Dependent Clause With an Independent Clause

A dependent clause is part of a sentence that “depends” on the independent clause to make sense. In other words, a dependent clause is not a complete sentence. It must be connected to the main clause to bring clarity to the sentence.

Certain words make part of a sentence dependent on the rest of the sentence. Think about the following words as comma clues. Whenever you see one of these words, stop and consider the need for a comma.

• after
• although
• as
• as if
• because
• before
• even if
• even though
• if
• in order to
• since
• though
• unless
• until
• whatever
• when
• whenever
• whether
• while

Here are some examples of sentences composed of a dependent clause, comma, and independent clause. Note that the dependent clause appears at the beginning of the sentence, in front of the independent clause.

      When Brad walked the dog, his feet became entangled in the leash.

      Since Emma walked to the store, she did not have to walk the dog.

      While Emma walked to the store, Brad walked the dog.

      Unless Emma chooses to walk to the store, she must walk the dog.

Where would you place the comma in the following sentence?

      Whenever Brad completes his chore of walking the dog he gets to go to the movies with his friends.

Use Commas In a Series Or List

Use a comma to separate items in a series of words or phrases in a sentence to make the meaning of the sentence clear.

      I’m ready to sit down and write after I have exercised, showered, and enjoyed two cups of coffee.

      I need my computer, note cards, and a pencil when I study.

A Note On the Oxford, Or Serial, Comma

An Oxford comma, or serial comma, is the final comma in a list. In the examples above, the serial or Oxford comma appears after the words “showered” and “cards.”

Some style guides, such as the AP Stylebook, don’t require the Oxford comma, but for the most part, using the Oxford comma is a good rule to follow to avoid misreading the sentence.

Consider this example:

While visiting the United States, Eduardo spent the most time with Nicholas, a college professor and a writer.

Without the serial comma, the reader isn’t sure if A) Nicholas is a college professor and writer or B) Eduardo spent time with three different people—Nicholas and a college professor and a writer. In instances like these, the comma should be used to clarify the meaning.

While visiting the United States, Eduardo spent the most time with Nicholas, a college professor, and a writer.

With the serial comma, the reader understands Eduardo spent the most time with three different people.

Bottom Line: Unless you’re using AP Style, or an editor or instructor tells you otherwise, consider using the Oxford comma (serial comma) to separate a list of things in a sentence.

Use a Comma With an Appositive

An appositive is a word that means “to place near.” In writing, an appositive’s grammatical function involves placing a noun or noun phrase near another noun to provide more information about that noun. Using an appositive is a simple way of adding extra information about the noun.

Use commas when the appositive is nonessential information. (Some stylebooks call these nonrestrictive appositives or nonrestrictive clauses.) In other words, when the information you provide enlightens the reader but isn’t necessary for understanding what you mean, set the appositive off with commas.

If, on the other hand, the appositive is essential to the sentence, meaning the sentence wouldn’t make sense without it, a comma is unnecessary. Some stylebooks call these restrictive appositives because the sentence is unclear without the added information. 

Here are some examples:

Brad walked the dog, a lively Jack Russell Terrier. (“A lively Jack Russell Terrier” helps describe the dog, but the information clarifies. It is not necessary, or essential, for understanding what Brad did. It is nonrestrictive.)

      Emma, hungry for a snack, walked to the store. (“Hungry for a snack” explains why Emma walked to the store, but is not essential information in understanding the sentence. It is nonrestrictive.)

Emma’s friend Samantha walked to the store. (The name Samantha is restrictive, meaning it is essential to understanding which of Emma’s friends walked to the store. A comma is not necessary when the noun is essential to understanding.)

Where would you place the commas in the following sentence that contains an appositive?

      John’s next-door-neighbor both a soccer player and technology whiz is also his best friend.

Use a Comma With a Parenthetical Element

Think of a parenthetical element as a quick little interrupter within a sentence. It provides additional information but isn’t necessary for the sentence to make sense.

Parenthetical elements are set apart from the main part of the sentence with commas.

Here are some examples:

      Brad was livid, as one might imagine, when the dog escaped from its leash and ran away for the third day in a row. (“As you can imagine” is the parenthetical element.)

      Emma, unlike Brad, enjoyed walking to the store. (“Unlike Brad” is the parenthetical element.)

Set off the parenthetical element with commas in the sentence below.

      That example as I have already shared doesn’t fully explain your behavior.

Use a Comma Between Coordinate Adjectives

Adjectives describe nouns.

When two or more adjectives are used to describe the same noun in equal ways, separate those adjectives with commas.

Brad walked the dog through the large, deep mud puddles. (Large and deep are adjectives that describe the noun, mud puddles.)

The scary, long-bearded man knocked on the window of my car. (Scary and long-bearded are adjectives that describe the noun, man.)

If you’re unsure if you need a comma, apply this test:

1. Reverse the order of the adjectives. If the meaning of the sentence doesn’t change, apply the commas.

2. Place the word “and” between the two adjectives. If the meaning of the sentence doesn’t change, apply the commas.

Are the commas necessary in the sentence below? Apply the two rules to see if the sentence contains coordinate adjectives. If it does, place the commas in their necessary places.

      The once-exhausted mother arrived back home from her long restful getaway.

Use a Comma After an Introductory Phrase

When a phrase is placed at the beginning of the sentence, separate the phrase from the main clause.

      Attaching the long leash to the dog’s collar, Brad walked the lively Jack Russell Terrier.

      Her stomach growling from hunger, Emma walked to the store.

Where does the comma go in the following sentence?

      Spotting his girlfriend in the restaurant Dan waved and quickly walked toward her.

Use Commas With Direct Quotations

Whenever you write dialogue and use quotation marks, use a comma to separate the quote from the rest of the sentence.

Here are two examples:

      Emma asked her mother, “May I please walk to the store and get a snack?”

      “I must walk the dog before I can play video games,” Brad explained to his friend Nick.

Where does the additional comma go in the sentence?

      “Brad walked the dog, and I went to the store for milk” Emma told her mother over the phone.

Use Commas In Geographical Names, Addresses, Dates, and Name Titles

Use a comma

• toTo separate a city or town’s name from the state.
  • Buffalo, New York
• Use a comma tTo separate a city or town’s name from the state when writing out an address on one line.
  •  Buffalo, NY, 14222
• Use a comma tTo separate a month’s day and year.
  • May 20, 1963
• Use a comma tTo separate the day of the week from the date.
  • Monday, May 20
• Use a comma iIn name titles that follow a name.
  • Dr. Mark Smith, M.D. 
  • Dr. Connie Miller, Ph.D.

Use a Comma In Longer Numbers

Separate long numbers into groups of three, going from right to left.

3,000

400,267

1,752,500

When NOT To Use Commas

Sometimes writers overthink their use of commas and end up confusing the reader. This next part highlights some of those times.

Avoid Creating a Comma Splice

A comma splice occurs when you join two complete sentences with a comma. If each part of the sentence could stand alone and make sense, you should use a semicolon or period in place of the comma. The period is preferred unless the second sentence is integral to the first.

      Brad walked the dog, the dog is a lively Jack Russell Terrier. (This sentence is a comma splice because two complete sentences are joined by a comma.)

Correct:

      Brad walked the dog. The dog is a lively Jack Russell Terrier.

Sometimes you can correct a comma splice by making one of the independent clauses into a phrase.

      Brad walked the dog, a lively Jack Russell Terrier.

“That” Does Not Require a Comma

When the word “that” is part of a clause that follows a noun, do not use a comma.

      The oranges that came from Florida are sweeter than the oranges from California.

Compound Subjects Don’t Use a Comma

 The subject in a sentence is the noun that the sentence is about. A compound subject is when the sentence has two or more subjects. Don’t separate the subjects with a comma.

      Emma, and Brad are siblings. (“Emma and Brad” is a compound subject. Remove the comma after “Emma.”)

Correct:

      Emma and Brad are siblings.

The Final Word on when to use a Comma

Commas are intended to make your writing clearer by separating words, phrases, and clauses. All the “rules” are not intended to generate anxiety as you write. The best way to overcome your worry is to strengthen your understanding. Take concentrated time to look at each sentence during the editing and proofreading stages of your writing. In doing so, you soon will find the application becomes second nature.