The comma might be the punctuation mark that many learners find the most challenging. However, after reading this post, you’ll be able to use it with confidence.

Separate items in a list of three or more by commas.

I went shopping to get some milk, bread, cheese, and some soda.

Question: Sometimes, I see the comma before the last item (“some soda” in the example above) is dropped. Why is that?

Answer: The last comma before the words “and” or “or” in a series of items is called the Oxford Comma. Some people think that this comma is unnecessary and therefore drop it. However, the absence of it may sometimes result in confusion.

Example:

I visited my relatives, Lily and James. This means that I visited my relatives whose names were Lily and James.

I visited my relatives, Lily, and James. This means that I visited my relatives. Also, I visited Lily and James.

Note: Both of the examples above are grammatically correct, but they have different meanings. Because of this, it is always recommended to use the Oxford Comma to avoid any confusion.

Use commas to separate coordinate adjectives.

Example:

It was a long, boring, and poorly-scripted show.

Note: If there are three or more modifying adjectives, you can put “and” before the last one.

Question: Sometimes, I don’t see a comma between the modifying adjectives. Why is that?

Answer: Here is the simple and clear rule: when the modifying adjectives before a noun are cumulative, you shouldn’t separate them by commas. When the adjectives are coordinate, you should use commas to separate them.

Examples:

No commas with cumulative adjectives: There are three big old blue cars in the garage.

Commas with coordinate adjectives: Jane has a creative, inquiring mind.

Use a comma when an adjective or adverb is repeated for emphasis.

The movie is very, very long. They should have made it a lot shorter.

Use commas to set off nonessential or nonrestrictive information.

Example:

My first English teacher, Mr. Jones, is a very kind-hearted person.

Explanation: You can have only one first English teacher, so no confusion will occur if you omit the teacher’s name. The listener won’t ask, “Which first English teacher?”

More examples:

Germany, one of the European countries, has a high-quality education system.

My twin brother, who owns six cars, just bought another in an auction.

I think English, the language spoken in many countries, has easier grammar rules than Hungarian.

Explanation: In the above examples, if you omit the parts set off by commas, you would still have complete sentences that do not confuse readers/listeners. These parts are merely further explanations, nothing more. Therefore, they’re not restrictive.

Question: What is restrictive information?

Answer: Restrictive information specify which item, person, etc. you are talking about. Take, for example, the situation below:

Jack has three brothers. Their names are Brian, James, and Jimmy.

Now, If I say that Jack gave his car keys to his brother, you would most probably ask, “Which brother?”

So to be clear, I change my sentence to this: Jack gave his car keys to his brother James.

As you can see, there is no comma setting off “James” because it is essential and restrictive. Without it, the listener becomes confused.

Commas with relative clauses

Commas with interruptions

Example:

We spent our vacation in a very nice coastal city. However, the hotel that we stayed in, to be honest, was awful.

Commas with numbers

It is recommended to place a comma after every three digits of numbers with four or more digits. Count three spaces to the left to put the first comma and then continue placing commas after every three digits. However, this recommendation does not apply to the numbers relating to years, page numbers, and street addresses.

Example:

This company claims to have over 9,540 happy customers. It sold around $10,050,030 worth of goods in the year 2019.

When writing degrees and certificates in front of a person’s name, make sure you set them off by commas.

Examples:

American English: John Smith, Ph.D., will be the next CEO of this company.

British English: John Smith, PhD, will be the next CEO of this company.

American English: Joe Smith, M.D., will be our keynote speaker this evening.
British English: Joe Smith, MD, will be our keynote speaker this evening.

Set off people’s names by commas when they are addressed directly. 

Examples:

I am talking to you, James.

When you have done all your chores, Tom, you can do whatever you want.

Jessica, I read your work last week, and I must say it is brilliant.

Commas with dates

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

Examples:

She was born on Monday, June 15.

She was born on June 15, 2020.

She was born on Monday, June 15, 2020.

Note 1: when the date appears in the middle of the sentence, it should be set off by commas.

Example:

The ceremony on Tuesday, June 16, 2020, was canceled.

Note 2: No comma is needed between the month and the year if they are the only elements in the date.

Example:

The ceremony in June 2020 was canceled.

Note 3: If you reverse the month and day, which is common in the British style, you won’t need to use commas.

Example:

The ceremony on 16 June 2020 was canceled.

When writing a location in a sentence, use commas to separate different types of locations (city, region, country, etc.).

 Examples:

She lives in Manhattan, New York, the U.S.A.

Our headquarters in Manhattan, New York, the U.S.A., is closed for the time being.

Use a comma to show contrast

Example:

They called my name, not yours.

Separate tag questions with a comma

Examples:

• This house looks magnificent, doesn’t it?
• Sadly, Pandas are going to become extinct, aren’t they?

When you join two sentences using coordinating conjunctions (for, and, nor, but, or, yet, and so), put a comma at the end of the first sentence.

Examples:

• Jim wanted to buy the new game console, but he didn’t have enough money.
• Ashley worked day and night to win the contest, and she succeeded in the end.
• We ran out of milk, so I went to the shopping mall to buy some.

Note 1: No comma is needed if the second sentence doesn’t have a subject.

Example:

She opened the door and went outside.

Note 2: Use a comma when you join two imperative sentences with a coordinating conjunction.

Example:

Complete this project as soon as you can, and send me a message once you’re done.

Note 3: We sometimes ignore this rule and use a comma to avoid confusion.

Example:

• I realized that the manager didn’t have the time to talk and left the office.

In the sentence above, the reader might get confused and think that the manager left the office.

• I realized that the manager didn’t have the time to talk, and left the office.

The comma in this sentence makes it clear that I left the office, not the manager.

Question: Why do I sometimes see no commas before “so”?

Answer: The word “so” can sometimes connect an independent clause to a dependent clause in the sense of “so that”. In this case, we don’t use a comma to separate the clauses.

Example:

I am saving money so I can buy a new phone = I am saving money to buy a new phone = I am saving money so that I can buy a new phone.

Question: Can I use a comma to join two independent clauses without using coordinating conjunctions?

Answer: No, you can’t. When you join two independent clauses using a comma and without a coordinating conjunction, you’ll create an error called comma splice.

Example:

Incorrect because of a comma splice: She completed her essay, she started watching TV.

Correct: She completed her essay, and she started watching TV.

Better: She completed her essay and then started watching TV.

If a sentence starts with a dependent clause, you should separate it with a comma from the following independent clause.

Examples:

• After you are done fixing the car, come and take a look at the TV. It’s not working.
• If you aren’t sure about the answer, leave the question unanswered.

Note: When the independent clause starts the sentence, no comma is needed.

Example:

Come and fix the TV after you are done fixing the car.

Note: Some compound-complex sentences (refer to this link for more information on the types of sentences) start with a dependent clause followed by two independent clauses. In such cases, a comma should be used between the two independent clauses.

Example:

After a long night at work, Sara went home to take a shower, and I took a taxi to the hotel.

Dependent clause 1: After a long night at work

Independent clause 1: Sara went home to take a shower

Independent clause 2: I took a taxi to the hotel

Note: If a dependent clause comes between two independent clauses and applies only to the second, the dependent clause should be set off with commas.

• I really loved the show, and if I have free time next week, I will go and watch it again.
• Sara went home to take a shower after a long night at work, and I took a taxi to the hotel.

Use a comma after an introductory word or phrase.

Examples:

• In my opinion, a better education system can solve many social problems.
• Yes, I am very busy right now.
• He was mean to everybody throughout the year. As a result, nobody showed up at his birthday party.
• Hello, I’m John.

Use a comma to introduce direct speech in quotations.

Example:

She said, “Tomorrow is going to be a great day.“

Note: When the quoted speech comes before she said, he reported, etc., the comma goes inside the quotations in the American style. In the British style, it comes after the closing quotation mark.

Example:

American Style: “Tomorrow is going to be a great day,“ she said.

British Style: “Tomorrow is going to be a great day“, she said.

Note: In cases that the quotation is considered a subject or object in a sentence, you may not need a comma.

Example:

What does “water under the bridge” mean in English?

Note: In quoted questions, the question mark replaces the comma.

Example:

“What time is it?” she asked.

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