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When to Use Commas with Coordinating Conjunctions | (B-Level, Intermediate)

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Whether or not to use a comma when combining ideas using coordinating conjunctions has to do with what exactly you are combining.

Simply put, when combining two complete sentences, you need a comma before the coordinating conjunction to separate the two clauses.

Let’s go into details in this lesson.


Rule 1. Use a comma to separate complete sentences

When the sentences before and after the coordinating conjunction are complete sentences, use a comma between them.

A complete sentence has a subject and a verb.

In the following examples, each sentence has a subject and a verb, so you need a comma to separate them:

Would like to watch a movie, or would you like to go for a walk.

John is cooking dinner, and Mary is watching TV.

Sandra is tired, so she is going to bed.

Rule 2. Do not use a comma before an incomplete sentence or part of a sentence

Sometimes two sentences have the same subject, so you omit the subject in the second sentence when you combine them. When you do that, you must omit the comma before the coordinating conjunction because you no longer have two complete sentences. Compare the following sentences:

John cooked dinner, and he did the dishes.

John cooked dinner and did the dishes. (no comma)

More examples

Comma before the coordinating conjunction

I want to study computer science, and my friend wants to study sociology.

I can speak Spanish well, but I can’t read it.

The governor was popular, yet he lost the elections.

No comma needed before the coordinating conjunction

Compare examples with and without commas

I arrived home, and I went to sleep right away.
(comma between complete sentences)

I arrived home and went to sleep right away.
(no comma needed))

Jack didn’t study, but he passed the test.

Jack didn’t study but passed the test.
(no comma)

Would you rather go to the beach, or would you rather stay home?
(comma; this is a repetitive sentence)

Would you rather go to the beach or stay home?
(no comma; better sentence)

Assess Your Learning

This unit has a number of exercises. See List of Exercises on Coordinating Conjunctions on the first page of the unit.

Related Lessons

This lesson is part of a complete unit on coordinating conjunctions.

To cover the whole unit, use the “Unit Navigation” button below.

Congratulations on completing this unit!

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