Nothing strikes fear and terror into the hearts of writers quite like the comma. Proper punctuation is important in writing as it makes our sentences clear and easier to read. Of all of the punctuation marks we use, the comma is especially versatile and has many different possible uses, sometimes within one sentence. This widespread usage comes at a significant price. There are many rules regarding commas, and this single punctuation mark is often the cause of many grammatical mistakes. If the comma causes you confusion, you are not the only one. Let’s see if we can make commas a little bit more manageable by learning more about them.

What is a comma (,)?

A comma is a punctuation mark that represents a short pause and is used to divide parts of a sentence. A comma usually resembles a dot with a tail (,) and is placed at the bottom of a line of text or writing. The comma has many, many different uses and is often the punctuation mark that people have the most difficulty with.

When do you use a comma?

There are a lot of different reasons why we use commas. We are going to very briefly look at a variety of instances when we commas.

Lists

When writing a list or series, we separate each member of the group with a comma. Typically, we use a conjunction such as and or or before the last member. For example,

• She can speak English, Spanish, French, and Japanese.

The final comma in a series is known as the Oxford comma. Depending on which style guide you use, the Oxford comma might be considered optional.

Joining independent clauses

A comma can be used to join two or more independent clauses together. If we use a comma this way, we follow it with a coordinating conjunction (for, as, nor, but, or, yet, so) before introducing the next independent clause. For example,

• I love dogs, and dogs love me.
• He wanted to be a sailor, but he couldn’t swim.

Following an introductory word or phrase

If we use a word, phrase, or dependent clause to introduce a sentence, we follow the introduction with a comma:

• Luckily, it didn’t rain on our parade.
• Thinking quickly, Osmodeus cast an invisibility spell.
• When the going gets tough, the tough get going.

Coordinate adjectives

If we use multiple adjectives before the same noun, we separate them with commas if they are coordinate adjectives. In short, coordinate adjectives can have their order switched around without changing the meaning of the sentence. You can learn more about identifying and using coordinate adjectives in our explanation of adjective order.

• The lazy, clumsy, hairy dog took a nap by the fireplace.

Nonrestrictive words, phrases, and clauses

When we use a modifying word or phrase to refer back to a noun, we separate it out with commas if it is nonrestrictive. In general, a nonrestrictive modifier is one that can be removed without changing the meaning or clarity of a sentence. For example,

• Nonrestrictive modifier: The current president of the actor’s fan club, Papa Razzi, is really popular. (The club only has one current president so their name is not needed to identify them)
• Restrictive modifier: The legendary detective Sherlock Holmes could solve any mystery. (We don’t know who the legendary detective is without naming them)

This same general rule applies to nonrestrictive clauses:

• The baseball card, which was badly damaged, was worth millions of dollars. (We would still know the identity of the particular card even without the nonrestrictive clause.)

Quotes

A comma is used to introduce a quote:

• She asked, “Where is the post office?”

If a quote is not at the end of a sentence and doesn’t end in a question mark or exclamation point, we typically follow the last word with a comma:

• “I was here yesterday,” the customer said.

Interrupting phrases

We use commas to separate out interrupting words or phrases from a main sentence:

• I would ask, if I may be so bold, that you please move your car.
• That guy over there is, trust me on this, someone you should avoid.

Direct address

When directly addressing a person or group, we separate them out using commas:

• Steve, I found your striped sweater.
• It seems, my friends, that we need a new plan.

Numbers, dates, and addresses

When writing large numbers, we use commas to divide the thousands, millions, billions, trillions, etc.

• The city is home to 1,234,567 people.

When writing dates in the Month-Day-Year format, we use a comma before the year.

• Napoleon Bonaparte was born on August 15, 1769.

When writing addresses, we separate each part of the address with commas:

• My friend Bart Simpson lives at 742 Evergreen Terrace, Springfield, West Dakota.

What about greeting cards? Learn about the right way to start and sign off that birthday card to grandma!

How to use a comma

There are a few common mistakes to watch out for when using commas.

Avoid the comma splice

A comma splice or comma fault occurs when a writer uses a comma without a conjunction to connect independent clauses. Most grammar resources consider this to be an error; a comma needs a conjunction in order to connect two independent clauses.

• Comma splice: The director wanted to film in Italy, it was too expensive.
• Fixing comma splice: The director wanted to film in Italy, but it was too expensive.

Instead of a comma, you can use a colon or semicolon to connect two independent clauses without using a conjunction. Alternatively, you could simply use a period and make them two separate sentences.

Be careful of compound subjects and predicates

Compound subjects and predicates are often connected by conjunctions such as and or or. However, the pieces of compound subjects and predicates are not separated from each other by commas.

❌ Incorrect: Jenny, and Benny, went to the store. ✅ Correct: Jenny and Benny went to the store.

❌ Incorrect: I bought a new computer, and used it to write my novel. ✅ Correct: I bought a new computer and used it to write my novel.

If a compound subject or predicate involves more than two elements, it will often be written as a series, which means it will then need commas:

✅ Correct: Jenny, Benny, and Lenny went to the store. ✅ Correct: I bought a new computer, set it up in my office, and used it to write my novel.

Subordinate clauses

Subordinate clauses are a type of dependent clause that modify another independent clause. Subordinate clauses typically begin with subordinating conjunctions such as because, since, and as. It is considered a grammatical error to use a comma before a subordinating conjunction. For example,

❌ Incorrect: I stayed home from school, because I was sick. ✅ Correct: I stayed home because I was sick.

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