Commas | When & how to use commas in English writing

by Alex

Commas are an important part of English writing. They create short imagined pauses in a sentence, and they separate words and ideas to help us clearly understand a writer’s intended meaning. When commas are used well, sentences and paragraphs are easier and more enjoyable to read, as commas add emphasis to specific words and clauses. If you want to improve your English punctuation skills, make your writing more dynamic, and reduce confusion in your sentences, knowing how to use commas is essential.

Rule 1

Use a comma after a conjunctive adverb at the beginning of a new sentence.

The mayor wants to build a new park. Unfortunately, there isn’t enough money for the project. House prices have gone up. Consequently, fewer houses have been sold this year. My friend put a box on the table. Suddenly, a cat jumped out of it.

Conjunctive adverbs are words such as “however,” “additionally,” “meanwhile,” and “conversely.” They are words that combine two independent clauses. An independent clause is a complete idea that has a subject and a verb. Short phrases such as “in conclusion,” “all in all,” “in addition,” and “for example” also follow this rule when they come at the beginning of a sentence.

Rule 2A

Use a comma before a coordinating conjunction that joins two independent clauses.

We wanted to take the car to the mechanic on Monday, but all of us were too busy. Dana really wants to be engineer, so she studies almost every single day. I’ve been waiting here for over two hours, and the bus still hasn’t arrived.

If you join two complete ideas with a coordinating conjunction (for, and, nor, but, or, yet, so), you should place a comma before the coordinating conjunction. For shorter sentences, this comma is often omitted. For example: “She screamed and I jumped.” But if you want to be safe, especially if you are writing for professional or academic purposes, use a comma.

Rule 2B

A comma is NOT necessary if the subject isn’t repeated in the second part of the sentence.

She had called her mom for advice and still didn’t know what to do. We rushed to the movie theatre but were too late to buy tickets. They would have to wait patiently inside the restaurant or not get a seat at all.

In the examples above, “still didn’t know what to do,” “were too late to buy tickets,” and “not get a seat at all” are not independent clauses. They do not express complete thoughts. Remember that rule 2A says you only use a comma before a coordinating conjunction if it separates two independent clauses. Independent clauses need a subject. However, when the subject is already implied and understood in the second part of the sentence, a comma is unnecessary.

Rule 3A

Use a comma after an introductory dependent clause or phrase. These include adverb clauses, adverb phrases, and participle phrases:

Adverb Clauses:

Before we go any further, I’d like to address a couple of things. If you would like more details, please speak to my manager. Even though it will be challenging, you should go for it.

A clause has a subject and a verb. There are independent clauses, which are clauses that express a complete idea and can stand on their own, and dependent clauses, which are clauses that need another clause to feel complete. If you start a sentence with a dependent clause that begins with words such as “if,” “although,” “whenever,” or “as soon as,” use a comma at the end of the dependent clause.

Adverb Phrases:

After the concert, we decided to go to a café. In the final minutes of the game, I received a shocking text message from my cousin. With the strength of an ox, he managed to lift the car.

Adverb phrases serve the same functions as adverbs, meaning they answer the questions how, where, when, or why. If you start a sentence with an adverb phrase, such as “at the end of the day,” “because of the weather,” “in a flash,” or “at the edge of the cliff,” you must use a comma. However, this rule isn’t followed consistently by all writers. If the phrase is short, some may choose to omit the comma. For example: “In 2005 he was only 7 years old.” While it is often better to be safe and use the comma in this case, do not be surprised if you see people omitting it. This usage is often accepted.

Participle Phrases:

Tired of waiting for the bus, Roberta decided to take her car instead. Excited to learn more about the boss’s plans, I attended her speech. Planning to study engineering, Kenzo spent a lot of time in the library.

A participle phrase starts with a participle adjective, which is an adjective that ends in -ed or -ing. Some other examples include “energized,” “internalizing,” “considering,” and “amazed”. If you start a sentence with a participle phrase, use a comma after the phrase.

You can extend this rule to all phrases that begin with an adjective. For example: “Sick of the noise in the next room, Brad finally shut the door”, or “Curious to learn more, I signed up for their email newsletter”.

Rule 3B

A comma is usually NOT necessary when a dependent clause or adverb phrase is in the second part of a sentence.

You can always call me if you have any questions. I can’t discuss this with you before the election results are released to the public. Construction workers were paving the streets all day long.

While commas are usually necessary after introductory clauses and phrases, they are not necessary if those same clauses and phrases come in the second part of a sentence. Look at the difference between these two examples:

When Tina’s mother arrived at the cottage, we all felt relieved. We all felt relieved when Tina’s mother arrived at the cottage.

Rule 4

Use a comma to introduce a non-defining relative clause.

The best candidate for this job is Mandy, who has over six years of experience in the industry. Tony arrived late, which really annoyed my mom. My sister, whom I love very much, really disappointed me last week.

A relative clause, also called an adjective clause, gives us more information about a subject. Relative clauses can be defining or non-defining. “She’s the one who asked for more juice” is an example of a defining relative clause. It gives us essential information about the subject by defining which subject we are talking about. Without the relative clause here, the sentence would simply be “She’s the one,” which doesn’t tell us enough.

Non-defining relative clauses give us extra information about a subject. The information is not necessary, but it can help clarify things or make things clearer in a sentence. Non-defining relative clauses can start with which, who, or whom. If you use a non-defining relative clause in a sentence, you must precede it with a comma. Here is one more example: “Yesterday, I spoke to Roberta, who really wasn’t happy to see me.”

Rule 5

Use a comma to introduce and end an appositive.

Toni Morrison, the renowned American novelist, has won numerous prestigious awards. Derek, full of passion and purpose, stomped to his boss’s office. My favourite classical composer is Chopin, the famous Polish pianist.

Appositives are short phrases that describe the noun that comes before them. Like relative clauses described in rule 4, appositives give us more detail about a subject. They sound like quick asides in conversation, and they have the same function in writing. If you want to add a quick bit of extra description about a noun, make sure you use a comma beforehand.

Rule 6

Use a comma to separate a list of three or more words or short phrases.

The colour options for this car are blue, red, and black. I’m going to invite my mom, my dad, and my older brother to dinner tomorrow. I’m tired of her whining, moaning, and complaining.

The final comma is sometimes omitted by writers for the purpose of flow. However, this final comma, called the Oxford comma or serial comma, is sometimes necessary to avoid confusion. For instance: “He was congratulated by his friend, wife and sister.” Is his sister also his wife and his friend in this case? It is clearer to write “He was congratulated by his friend, wife, and sister.” There are no cases where leaving out the serial comma is clearer, so you should always use it.

Rule 7

Use a comma to separate two adjectives from the same descriptive category.

She was a kind, gentle woman. She was a gentle, kind woman.

This is most often the case when the adjectives are opinions about a person or thing, such as the words “kind” and “gentle” above. Commas are not necessary for combinations of words such as “He owns a big old truck.” In this case, “big” and “old” are from two different descriptive categories—size and age—so you can leave out the comma.

Rule 8

Do NOT use a comma to separate two independent clauses.

He ran down the stairs, I chased after him. He ran down the stairs, and I chased after him. He ran down the stairs. I chased after him. He ran down the stairs; I chased after him.

The incorrect sentence above is an example of a type of error called a comma splice. This means two independent clauses, which are two complete ideas, have been separated by a comma instead of a period, semi-colon, or a comma and a coordinating conjunction such as and, so, or but. High school teachers and university professors will catch this mistake every time, so make sure to avoid it.

Rule 9

Use a comma after short words, phrases, and names that start a sentence, such as “Yes,” “No,” “Oh,” and “My, my.”

Why yes, I did see him at the festival. Oh my, what do we have here? No, you may not have another free drink. David, please call me when you get a chance.

If you start a sentence with a single word or short combination of words as shown above, you should typically use a comma. This is also true when names come at the beginning of a sentence.

Rule 10

Use a comma before and after phrases and sentences that interrupt the flow of a sentence, such as “by the way,” “however,” and “too.”

Your father went. Your mother, however, did not. Your father went. Your mother did not, however. You like jazz? I, too, like jazz. The cause of my lateness, by the way, was traffic.

In cases where you want to add a small word or phrase to focus your sentence or to add an important clarification in the middle of your thoughts, use a comma.

Rule 11

Use a comma after a greeting or term of endearment.

Good morning, everyone. Hello to you as well, Bridget. My dear, you should know better.

In some cases, this rule is ignored in email writing. For example, instead of writing “Hello, Tom”, many people will start an email with “Hello Tom”. Both are accepted, though the standard rule states there should be a comma after a greeting, particularly when it is followed by a person’s or group’s name. When words such as “Dear” and “My darling” precede a person’s name, the comma comes at the end (Dear Edward, My darling Agatha, etc.).

Rule 12

Use a comma to separate days from dates, and dates from years.

It happened on April 6th, 2015. The parade is on Saturday, October 20th. Today’s date is Wednesday, November 10th, 2022.

No commas are necessary if you just mention the month and year (March 2018), or the month and day (November 7th). Note this more formal structure and the lack of commas: It happened on the 17th of January 2021. While some might argue that a comma is necessary after January, when months are followed by years, commas are unnecessary.

Rule 13

Use a comma to separate cities from states and provinces, and states and provinces from countries.

She’s from Boise, Idaho. He was born in Calgary, Alberta. I grew up in Queensland, Australia.

You will sometimes see examples of no commas before the name of a country when it is preceded by a state or province. This is accepted by most people, but it is less common to ignore the comma rule when separating the name of a town, city, or village from its state or province.

Rule 14

Use a comma to introduce or interrupt direct quotations.

“I don’t want to be here,” he said. “Of course,” Daniel said, “You can always come back tomorrow.” “I’ve never been here before,” she admitted.

If you use a dialogue attribution such as he said or she asked after a direct quotation, place the comma inside and at the end of the quotation, even if it is the end of a complete thought. This is commonly used in fiction and in news report writing. This rule is only broken by question marks and exclamation marks. Note the examples:

“Is this where the accident happened?” she asked. “I don’t like it!” he said.

Also note that the she and he used in these examples still begin with lowercase letters.

Rule 15

Use a comma to introduce a tag question.

I’m here, aren’t I? This won’t take long, will it? Mark’s not here today, is he?

Tag questions clarify or confirm information. When you use one, make sure you use a comma beforehand.

Rule 16

Use a comma to separate brief contrasting pieces of information.

She’s not rich, but poor. This is Dominque’s, not yours. I feel tired, yet happy.

“Not” and “but” are commonly used in this way. Short phrases that state a contrast, as in the examples above, require a comma beforehand.

Rule 17

Use a comma before the word etc.

You’ll need books, pencils, pens, etc. Her mom, dad, etc., all attended her graduation. He needs to learn more about the sun, the planets, etc.

Etc. means “and other similar things” or “and so forth.” This is not a case of the Oxford comma where it’s sometimes optional. This is a case where a comma must be present. Also, note the second example above, where etc. comes in the middle of a sentence and retains the period at the end. In this case, it is still followed by a comma.