Commas are one of the most frustrating grammatical concepts, even for native English speakers.
There are specific rules for when you should and shouldn't use commas whether it’s before an appositive phrase or in the middle of a list of items.
So, when exactly do you need to use a comma?
In this article, we’ll look at the rules of comma usage along with examples of how to use commas in English sentences.
How to Use Commas
A comma is a punctuation mark that indicates a small break in a sentence. You can think of the comma as a pause or a separation.
Commas are often used to separate multiple different elements or ideas. If you use them correctly, they make sentences a lot easier to read—but if you use them incorrectly, you can come across as unprofessional or even convey the wrong meaning to your readers.
Learning the rules of comma usage can help you make your writing clearer, stronger, and more professional.
12 Comma Rules
Here are twelve rules you can use to determine when you need to use a comma.
1. Use a Comma Between Two Independent Clauses
You should always separate independent clauses with a comma. The comma should be followed by a coordinating conjunction, such as “and,” “but,” or “or.”
Sarah likes to swim, and Mary likes to paint.
I want a pet dog, but my mother is allergic.
We can have lasagna for dinner tonight, or we can have it tomorrow for lunch.
I wanted to drive, but my father wouldn’t let me.
2. Use a Comma to Separate Items in a List
Whenever you’re writing a list of three or more words, you should include a comma between each word. The Oxford comma, which is the comma that comes after the penultimate item in your list, is optional.
My favorite ice cream flavors are chocolate, vanilla, and strawberry.
Bob, Bill, and Bryan were at the party together.
Avoid eating red meat, eggs and butter if you want to lower your cholesterol.
Do you prefer reading fantasy, science fiction or romance?
3. Use a Comma After an Introductory Phrase
You should use a comma when you start a sentence with an introductory prepositional phrase. This is a phrase that gives you the time, location, or context for the rest of the sentence.
On my sixteenth birthday, I ran away from home.
When it stops raining, we can go to the park.
I can’t talk right now, but after work, I’ll call you back.
Before Sarah became my sister-in-law, she was my best friend.
4. Use a Comma After an Introductory Adverb
You should use a comma when you modify an entire sentence or independent clause with an adverb. Some common introductory adverbs include “strangely,” “unfortunately,” and “luckily.”
Apparently, my father had already handled the situation.
Luckily, nobody was hurt in the accident.
Frequently, my boyfriend complains about my tardiness.
Weirdly enough, there was another fantasy writer at the party.
5. Use a Comma After a Subordinate Clause
A subordinate clause is a sentence fragment that begins with a subordinating conjunction, such as “after,” “although,” or “as long as.” When you start a sentence with a subordinate clause, you should include a comma.
After I got home from school, my mother told me the news.
Although the teacher was strict, he was always fair.
While we were at the store, we ran into my old friend Kathy.
As long as you keep paying rent, you can live at my house.
6. Use a Comma to Indicate Non-Restrictive Appositives
Appositives are nouns or noun phrases that offer extra information about a different noun or noun phrase. You can think of them as “bonus facts,” and unless they offer essential information, they should always be separated from the rest of the sentence with commas.
My brother John, a recent Harvard graduate, is trying to find a job.
Amanda, the girl I worked with last summer, is also coming to the party.
I loved reading Great Expectations, a novel by Charles Dickens.
We spent the summer in Seville, a city in Spain.
7. Use a Comma With a Participle Phrase
Participle phrases are phrases that modify a noun or a pronoun and give extra context about that noun or pronoun. They include both present participles, which end with -ing, and past participles, which usually end in -ed.
Ben got dressed in a hurry, excited to go to the party.
Trying not to panic, I called my mom for advice.
I went above and beyond yesterday, hoping to impress my boss.
She studied hard, determined to ace the math test.
8. Use a Comma Before or After Direct Quotations
When you include a quotation within a sentence, you should use commas to separate it from the rest of the sentence.
“Hey,” he said, “it’s good to see you again.”
I looked him in the eye and said, “Tell me the truth.”
She turned to me and shouted, “What in the world were you thinking?”
“Look,” she whispered, “there’s a red fox standing behind that tree.”
9. Use a Comma Between Coordinate Adjectives
Coordinate adjectives are two adjectives that apply to the same noun and are equally important. Whenever you have multiple coordinate adjectives, you should include commas between them.
I chose a thick, cream-colored paper for my wedding invitations.
My neighbor has a big, scary dog.
I’m craving a ripe, juicy apple.
Have you read any good, relaxing books lately?
10. Use a Comma Before or After a Vocative
Vocatives are when you address someone by their name or title, such as “Abby” or “madam.” You should always separate a vocative from the rest of the sentence using commas.
What time is your meeting, Dad?
Hey, Alex, knock it off.
Excuse me, ma’am, does this belong to you?
Sir, I’m afraid you’re not allowed to park your car here.
11. Use a Comma in Locations and Addresses
Anytime you use a geographical name that includes multiple elements, you should separate the elements with commas.
Street addresses have their own comma conventions. You should separate certain elements of a street address with a comma. Include a comma between the street and the city, and another one between the city and the state.
I grew up in Seattle, Washington.
She went to medical school in Toledo, Ohio.
You can reach me at 183 Main Street, Denver, CO 80014.
My mom lives on Second Street, San Francisco, CA.
12. Use a Comma in Dates and Numbers
When you write a date, you should always use a comma to separate the year from the rest of the sentence.
You should also use commas in numbers that are more than four digits long to break the numbers up into groups of three, which makes it easier to read them.
It happened on November 9, 2020.
On February 26, 1998, I got my beautiful dog.
The population of my town is about 35,000.
There are almost 8,000,000,000 people in the world.
When to Use Comma Examples
Now that we’ve covered the rules, it’s time to see how they work in action.
Let’s look at some examples of what correct comma usage looks like in sentences.
Correct: I wanted cereal, but we were out of milk.
Correct: Sadly, the package arrived too late.
Correct: By the time I got home, you had already left.
Correct: My four sisters are Mary, Jane, Lily, and Olivia.
Correct: Unfortunately, we’re all out of croissants.
Correct: Matthew, where did you put the markers?
Correct: She said, “Go away, I’m busy.”
Correct: “Hang on a second,” I said.
Correct: Already exhausted, she struggled to complete her chores.
Correct: You’ll need a thick, insulated sleeping bag for this camping trip.
Correct: My favorite sister, Priya, just got into law school.
Correct: Before you go to the party, you have to finish your homework.
Correct: I was born on March 18, 1992.
Correct: That house costs more than $1,000,000 USD.
How ProWritingAid Can Help You With Comma Usage
If you, try running your work through ProWritingAid.
The grammar checker will catch any punctuation errors in your writing, including any missing commas when you’re supposed to be using them or unnecessary commas when you’re not supposed to be using them. If you’re not sure which comma rule you’re forgetting, you can click on the in-app explanation to find out more.
Good luck, and happy writing!