Words at work

– 6 min read

How to use commas: rules and examples

Jessica Malnik

Jessica Malnik

OK, we might be exaggerating a little bit, but a misplaced comma can lead to confusion and hilarious misunderstandings. For example, “Let’s eat Grandpa!” has a completely different meaning from “Let’s eat, Grandpa!” 

A well-placed comma adds clarity to your sentences. A comma is a versatile punctuation mark, which is why it often gets misused. The comma helps you separate words, phrases, and ideas within a sentence. It represents a small pause or break. 

With such varied uses, it’s easy for even the most grammar-savvy person to get confused sometimes. In this post, we explain the different types of commas, some critical grammar rules, and how to use commas in your writing to prevent you from misusing this common punctuation mark.

4 types of commas

When trying to decide if your sentence needs a comma, it can help to think about four types, or common uses, of commas. 

1. Interrupter or bracketing commas

Sometimes sentences have interruptions, or little thoughts, in the middle of the sentence. These interruptions should be bracketed by commas, with a comma before and after the interruption. 

Correct: Her apartment, however, didn’t have a balcony.   Incorrect: Her apartment however didn’t have a balcony.

Correct: Tom, who owned a truck, was able to drive on the dirt road. Incorrect: Tom who owned a truck was able to drive on the dirt road.

Interrupter commas help the flow of the sentence and add clarity. You can often find where interrupter or bracketing commas are needed by reading the sentence aloud. Some common interrupter words and phrases include: however, unfortunately, in fact, needless to say, therefore, and sadly.

2. Conjunction commas

Place a comma before the conjunction when combining two independent clauses with a conjunction. Conjunctions include and, but, and or

Correct: We found the secret location, but the treasure wasn’t there. Incorrect: We found the secret location but the treasure wasn’t there. 

Correct: I like dogs, and I like snakes. Incorrect: I like dogs and I like snakes.

Does this mean you always put a comma after a conjunction? No! Remember, this rule applies when you’re joining together two independent or main clauses. 

3. Introductory commas

You use an introductory comma after a clause, phrase, or word at the start of a sentence. This phrase is a dependent clause that doesn’t act as a whole sentence.

Correct: If you’re feeling sick, you should stay home from work. Incorrect: If you’re feeling sick you should stay home from work.

Correct: When it stops raining, we’ll walk the dog.  Incorrect: When it stops raining we’ll walk the dog. 

4. Serial commas

When you’re writing a list or series of elements containing three or more items, you use a serial comma (aka. Oxford Comma) after each entry to make it easy to read and understand.  

Correct: Maya ate eggs, bacon, toast, and fruit for breakfast. Incorrect: Maya ate eggs bacon toast and fruit for breakfast.

In the incorrect example, there are no commas, which makes it hard to read the list. There always should be a comma after eggs and bacon

However, there is a debate on whether you need a comma after toast. If you’re using a serial comma, you add a comma before the last conjunction in your list, as in the example above. 

Using the serial comma is generally a matter of choice unless you must follow a set style guide. Style guides that require the serial comma include the Oxford Style Manual, Chicago Manual of Style, and the MLA Style Manual. The AP Style Guide doesn’t require the serial comma. You should also use it in situations where there is ambiguity, as in the above example. 

The 8 rules for commas

Commas have many uses. It can be helpful to keep these eight rules in mind so you can use them correctly.

1. Use a comma when addressing a person 

When the speaker in the sentence addresses the audience by name, it’s called a direct address

Correct: Mom, I need to borrow the car. Incorrect: I think Jamal you’re wrong. 

2. Use a comma with a question tag

Question tags are often used in sentences when the author is trying to get readers to agree with the statement. In this case, place the comma before the question tag.

Correct: You like the book, don’t you? Incorrect: This movie is boring right?

3. Use a comma with nonessential appositives

An appositive is a noun, pronoun, or phrase beside another noun or pronoun in the sentence that helps explain or identify it. A nonessential appositive can be removed without it changing the meaning of the sentence. In this case, the nonessential appositive word or phrase should be set off with commas.

Correct: My dog, Shadow, is a labradoodle.  Incorrect: Jane Austen my favorite author completed six novels. 

4. Use a comma with direct quotations 

Use a comma to introduce dialogue. When you have a phrase like “she said” that identifies the speaker of the dialogue or quote, you use a comma to separate the phrase from the quote. The phrase, called an attributive tag, can come after, before, or in the middle of the quote.

Correct: She said, “You shouldn’t put foil in the microwave.” Incorrect: “If you put foil in the microwave.” Jade said. “the microwave could catch on fire!”

5. Use a comma inside quotation marks

In American English, use a comma before closing a quotation mark.

Correct: “Put the book on the table,” said his mom. Incorrect: “Let’s call for pizza during the commercial break”, requested his roommate.

6. Use commas with nonrestrictive clauses

Nonrestrictive clauses are clauses that aren’t essential to the meaning of the sentence. 

Correct: Rubies, which are expensive, are often used in jewelry. Incorrect: Matthew who went to a local university plays guitar.

7. Use a comma to separate coordinate adjectives

Coordinate adjectives are two or more adjectives working together to modify the same noun. Coordinate adjectives still make sense if you place the word and between them or change the order. The adjectives are roughly equal in importance. 

 Correct: The loud, shrill alarm woke everyone up. Incorrect: The teacher needed a long restful vacation.

8. Using a comma with dates

Use a comma to separate the month and day from the year.

Correct: Joey was born on May 27, 2001.

Use a comma when you reference a day of the week and a date.

Correct: The high school graduation will take place on Saturday, June 15, 2021.

You don’t need a comma if you use the day-month-year format or refer only to a month and year.

Correct: The state had a record-breaking heatwave in August 2019. Incorrect: The state had a record-breaking heatwave in August, 2019.

How to use commas in your writing

When you’re writing, it can help to keep in mind situations when you don’t need a comma. Here are some ways commas are often misused. 

Look out for a comma splice

A comma splice occurs when you have a comma between two independent clauses without a conjunction. You can fix this mistake by either adding a conjunction, making each independent clause its own sentence, or replacing the comma with a semicolon.

Correct: I’m not happy with my grade, so I’m going to do the extra credit assignment. Incorrect: I’m not happy with my grade, I’m going to do the extra credit assignment.

Don’t automatically put a comma before “but”

You only need a comma before but when you’re connecting two independent clauses.

Correct: I would like to join the band, but I broke my guitar. Incorrect: The squirrel started to cross the street but it jumped back when the car drove by.

You don’t need a comma before but when you have one independent clause and one dependent clause.

Correct: The boy started to eat the kale but stopped at the smell. Incorrect: The boy started to eat the kale, but stopped at the smell.

Avoid putting a comma before that in a restrictive clause

The word that is often used to introduce a restrictive clause. In those situations, you don’t need a comma.

Correct: The ball that broke the window was pink. Incorrect: The turtle, that has a dent on its shell was rescued.

Don’t use a comma if the sentence’s dependent clause follows the independent clause

While you should use a comma when the dependent clause comes at the start of the sentence, you shouldn’t use a comma when it comes after the independent clause.

Correct: Jane was late for school because she had a flat tire. Incorrect: I bought popcorn after, seeing someone eating it. 

In sum, commas help add clarity to your writing. While they add a short pause or break, you don’t need one every time you naturally pause in a sentence. Using that strategy can result in too many commas. Yet, there are specific rules and guidelines to help you know when a comma is needed.

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