When to use a comma in your writing

When do you use a comma for English language writing? The answer is: It depends. Even professional writers trip over the many wonderful rules around comma usage. But don't worry — below, you'll find guidance for some of trickier questions concerning commas.

So, when do you use a comma? Let's take a closer look at comma rules, comma choices, and all manner of comma mistakes.

We’ll cover how to use a comma to:

• To connect two independent clauses
• To set off a non-essential clause or phrase
• Before the last item in a series of three or more items
• After an introductory phrase
• With parenthetical elements
• To distinguish coordinate adjectives that refer to the same noun
• In direct quotations or speech
• For emphasise at the end of a sentence

We'll finish by covering some frequently asked questions about commas.

Now, let's dive in!

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A comma can be used to connect two independent clauses when there is a pause in the sentence. Remember that an independent clause is a group of words that can stand alone as a sentence.

Let's see this in action. Take the two clauses:

I went for a walk.

and

I felt better.

You can use a comma and a coordinating conjunction ("and") to join these two sentences. The result is:

I went for a walk, and I felt better.

Note that if you didn't use the coordinating conjunction, this sentence would be an example of the dreaded comma splice. In this instance, you could also separate the independent clauses using a semi-colon.

Commas can be used to set off non-essential (also known as nonrestrictive clauses and phrases. Non-essential clauses and phrases provide additional information about a subject but are not essential to the meaning of the sentence.

For example, take this sentence:

The cat which is black sleeps on the porch.

The fact that the cat is black is not essential to the point of the sentence, which is to tell the reader that the cat is sleeping on the porch. It could be rewritten without that information as:

The cat sleeps on the porch.

If you want to keep the non-essential information, when you would set off that clause using a pair of commas, like so:

The cat, which is black, sleeps on the porch.

What about restrictive clauses?

It's important to remember that you shouldn't use commas to separate essential information — also known as restrictive clauses — from the rest of the sentence. You can usually tell if it's essential information because it will use the word 'that' instead of 'which'

The child that bumped her head is crying.

The cat that makes a racket is hungry.

Note that there can be essential parts of the sentence that do no have 'that', but still don't require comma.

The politician who took money from mobsters is corrupt.

The horse with a horn on its forehead is actually a unicorn.

The basic rule for using commas in a list is to insert them before the last item in a series of three or more items. This ensures you can separate items in a list, and prevent them from being confused.

Using this comma — also known as the Oxford comma or serial comma — can save you from misunderstandings and embarrassment. The final comma is sometimes debated, so check your style guide before you take this advice to heart.

For example, consider the following real-world sentence:

Rachael Ray finds inspiration in cooking her family and her dog.

Without commas, the logic of this sentence is that television personality Rachel Ray loves to cook her family and her dog. Though celebrities can indeed live strange lives, this seems unlikely to be true.

To fix this mistake, simply pop some commas between the items in the series:

Rachael Ray finds inspiration in cooking, her family, and her dog.

Okay, that's a bit more relatable! Phew. Note that if there were only two items in the series, you wouldn't need a comma, and the coordinating conjunction "and" would do the trick.

Commas can also be used after an introductory phrase before the main clause, though this rule is not strict and much informal writing does not follow it. Generally, most guides will tell you to use a comma if the introductory phrase is longer than 3-5 words. The variance here should tell you that this is not a strict rule.

What is an introductory phrase? This phrase is used to literally introduce a main clause, and can't stand on its own as a sentence.

Here are two examples of introductory phrases:

When I was walking to work, I saw a delightful pigeon.

While practising my spells, I turned my mother into an elephant.

These phrases are long enough to require a comma in most cases.

Here are two shorter examples of introductory phrases:

During the night, I went to the refrigerator and ate all the chocolate cake.

In December, we went to the beach and ate ice cream.

For these sentences, the comma after the introductory phrase is completely optional.

What about introductory clauses and words?

Commas can also be used after introductory dependent clauses and words. Remember, a dependent clause can’t stand alone as an complete sentence, unlike an independent clause.

For example:

Yes, this is a correct use of a comma for an introductory word.

When the sun stops shining, we'll go to bed.

Here, the dependent clause "when the sun stops shining" is introducing the independent clause "we will go to bed."

A parenthetical element is any information that is not essential to the meaning of the sentence, but which provides additional context or clarification. You usually see these in the middle of a sentence.

You might use a parenthetical element to explain why you are doing something or to give an example. Parenthetical elements are usually set off from the rest of the sentence by commas

For example, let's say I was pleased to eat a chicken for breakfast. I might write:

I ate a chicken happily for breakfast.

While I was very happy to eat chicken, this sentence is incorrect. To correct this sentence, I need to add commas around the parenthetical addition ("happily").

I ate a chicken, happily, for breakfast.

Commas are used to separate coordinate adjectives. What are they? Coordinate adjectives describe the same thing about a noun and are often of equal weight or importance. In the sentence “a tall, dark-haired man,” both adjectives are equally important in describing the man. If you removed either one, the sentence would still make sense.

Let's take a look at a few examples:

A plump, green turtle

A shaggy, loud dog

A hungry, unimaginative writer.

An appositive is a word or phrase that renames the noun or pronoun that comes before it. In order to set off an appositive, you need to use commas. For example:

My little sister, Lila, just celebrated her birthday.

Here, "my little sister" is the noun being renamed by the appositive "Lila."

Commas are also used to set off nonrestrictive appositives, which provide additional information about the noun but are not essential to its identity. For example:

George Washington, the first president of the United States, was born in 1732.

Here, "the first president of the United States" is nonessential information about George Washington and is set off by commas.

Commas should be placed before the quotation marks at the start of direct address, after any introductory phrases, and after each speaker's dialogue. For example:

"I'm going to the store," said John.

"I'm sorry," he said. "I didn't mean to hurt your feelings."

According to renowned linguist Noam Chomsky, "It's as if we're higher apes with a language faculty inserted."

Only use a comma to separate a dependent clause at the end of a sentence for added emphasis, usually when negation occurs. Some examples:

I went to New Zealand, not Australia.

He was a tall child, though not unusually so.

The writer was unimaginative, even lazy.

What's the difference between a comma and a semi-colon?

A comma is a punctuation mark that indicates a pause in a sentence, typically before introducing a coordinating conjunction or after an interjection. A semi-colon, on the other hand, is used to join two independent clauses. The semi-colon can also be used before conjunctive adverbs and transitional phrases.

A semi-colon indicates a stronger break than a comma, but not as strong as a period. For example, consider the following sentence: "I'm going to the store; do you need anything?" In this case, the semi-colon is used to connect the two clauses "I'm going to the store" and "do you need anything." Without the semi-colon, this would be two separate sentences.

What's the difference between a comma and a dash?

The most common type of dash is the em dash, which is used to create a dramatic break in a sentence. For example, an em dash can be used to emphasise a particular word or phrase: "I'm not going to do it—you can't make me!"

Like a comma, an em dash can be also be used to set off an appositive or a series of words: "The suspect—a tall man with dark hair—was last seen running from the scene." As you can see, the dash is a versatile tool that can add flair and emphasis to your writing. So next time you reach for a comma, consider whether a dash might be more appropriate.

Should I really use an Oxford comma?

Perhaps the most controversial part of this guide is the casual way in which we’ve suggested using the Oxford comma (or serial comma). As mentioned above, the Oxford comma is a comma that is used before the coordinating conjunction in a series of three or more items. For example, the sentence "I love apples, oranges and bananas" would be written with a serial comma as "I love apples, oranges, and bananas."

The use of the serial comma is often debated among writers. Some people argue that it is unnecessary and can lead to confusion, while others maintain that it helps to clarify the meaning of a sentence. At Shorthand, we personally prefer to use the serial comma, but we (reluctantly) understand that there are valid arguments on both sides of the debate. What do you think?