Comma Rules — When to Use a Comma

Commas are used to separate items in a list, after introductory phrases, before coordinating conjunctions in compound sentences, and around non-defining relative clauses. Knowing when to use commas makes writing clearer.

When to Use a Comma

1. Lists

Separate three or more items with commas:

I need to buy apples*,** bananas**,** and oranges.* She is funny*,** kind**,** and clever.*

Note

The comma before the final 'and' is called the Oxford comma. It is optional in British English but recommended for clarity.

2. After an Introductory Phrase or Clause

When a sentence starts with an adverb or phrase, add a comma before the main clause:

In the morning*,** I always eat breakfast.* After the rain had stopped*,** we went outside.* However*,** I didn't agree with him.*

3. Before Coordinating Conjunctions (joining two main clauses)

Use a comma + FANBOYS (for, and, nor, but, or, yet, so):

I wanted to go out*,** but it was raining.* She studied hard*,** so she passed the exam.*

4. Around Non-Defining Relative Clauses

(Extra, non-essential information — see Relative Pronouns lesson):

My dog*,** which loves water**,** jumped into the lake.*

5. Between Adjectives (if they both describe the noun equally)

It was a hot*,** sunny day.* ✓ (both describe the day equally) She wore a little red dress. ✗ (no comma — size + colour, not equal)

Common Comma Mistakes

Mistake	Correct
I like cats, I have three. (comma splice)	I like cats. I have three. or ..., and I have three.
She is, a good student.	She is a good student.

Real world: shopping list and recipe

Buy apples, bananas, and oranges for the fruit salad. After mixing the flour, eggs, and milk, pour the batter into the tin. However, if you prefer a thicker batter, add less milk.

Real world: news report

After the storm had passed, residents returned to their homes. The fire destroyed three buildings**,** but no one was injured. The mayor**,** who visited the area this morning**,** promised immediate support.

Tip Commas appear everywhere in English writing: recipe instructions ("Mix the flour, sugar, and butter"), news reports ("After the event, the minister spoke to reporters"), and essays ("She worked hard, so she achieved her goal"). Getting comma placement right makes your writing clearer and more professional.

Practice Problems

Add commas: 'After dinner we watched a film ate popcorn and went to bed.'

Show answer

'After dinner, we watched a film, ate popcorn, and went to bed.' (introductory phrase + list)

Is a comma needed? 'I was tired but I kept studying.'

Show answer

Yes: 'I was tired, but I kept studying.' (comma before coordinating conjunction joining two main clauses)

Add commas if needed: 'My sister Maria is a doctor.'

Show answer

If you have only one sister: 'My sister, Maria, is a doctor.' (non-defining). If you have multiple sisters, no commas (defining — which sister: the one called Maria).