Short answer: Use commas to separate items in a list, to join two full sentences with a conjunction, after introductory words, and around extra information. Do not use a comma alone to join two full sentences (a comma splice).
1. Items in a series (and the Oxford comma)
Put commas between three or more items: We bought apples, oranges, and pears. The comma before and is the serial or Oxford comma. Many American style guides, including Chicago, recommend it. Newspapers that follow AP style usually leave it out unless the sentence would be unclear.
2. Two full sentences joined by a conjunction
Use a comma before for, and, nor, but, or, yet, so (FANBOYS) when they join two complete sentences: I like tea, but she likes coffee.
3. After an introductory word or phrase
After the meeting, we went to lunch. However, we left early. In 2024, the company moved to Texas.
4. Around extra (nonessential) information
My brother, who is a pilot, lives in Ohio. If you can remove the phrase and the sentence still makes sense, set it off with commas. (See our guide to that vs. which.)
5. Between coordinate adjectives
Use a comma when you could put and between the adjectives or reverse them: It was a long, hard day. No comma is needed in a small wooden box, because the order cannot change.
6. Dates, addresses and direct address
- On October 5, 2026, we moved. (Chicago style also puts a comma after the year.)
- She lives in Austin, Texas, now.
- Thank you, Maria.
7. Do not put a comma between a subject and its verb
Wrong: The students in my class, passed the exam. Right: The students in my class passed the exam. Also avoid a comma before because in the middle of a sentence: We were late because of traffic.
8. The comma splice
A comma splice joins two full sentences with only a comma: I was tired, I went home. Fix it in one of three ways:
- Use a period: I was tired. I went home.
- Use a semicolon: I was tired; I went home.
- Add a conjunction: I was tired, so I went home.
Take the comma rules quiz
1.Which sentence uses a serial (Oxford) comma?
2.Which sentence is a comma splice?
3.Choose the correct sentence.
4.Which sentence punctuates the extra information correctly?
5.Which sentence has the correct comma?
6.Which sentence is correct?
7.Which sentence is correct?
8.Which is correct in formal American style?
9.Which sentence joins two full sentences correctly?
10.Which sentence is punctuated correctly?
Frequently asked questions
Do I need the Oxford comma?
It is optional, but many American style guides recommend it because it prevents confusion in lists.
What is a comma splice?
It is two full sentences joined by only a comma. Fix it with a period, a semicolon or a comma plus a conjunction.
When should I use a comma after an introductory phrase?
Use one after most introductory words and phrases, such as However, After dinner, and In 2024.
