Use a Comma to Separate Complete Sentences
Rule 1. Use a comma between 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.)
For example, in the following pairs of sentences, each sentence has a subject and a verb, so you need a comma to separate them:
John is cooking dinner, and Mary is reading a book.
Sandra is tired, so she is going to bed.
Would you like to read a book, or do you prefer to watch TV?
Rule 2. Do not use a comma before an incomplete sentence
Sometimes both sentences use the same subject, so you can make it shorter by deleting the subject in the second sentence when you use a coordinating conjunction.
In the following example, there are two complete sentences, so you use a comma before the coordinating conjunction “and:”
John cooks dinner, and Mary does the dishes every night.
You do not need a comma before “and" in this example because the second part does not have the subject (John).
John cooks dinner and does the dishes every night.
Example sentences without commas
I wake up early and go to the park every Sunday.
The children go to school and learn their lessons every day.
Janice stays home and reads a book on Sundays.
Compare sentences with and without commas
We can read Spanish , but we can’t speak it. (with a comma)
We can read Spanish but can’t speak it. (without a comma)
Mary goes to Japan every year, and she stays with her friend there.
Mary goes to Japan and stays with her friends there every year.
Do you want to stay home, or do you want to go out? (with a comma)
Do you want to stay home or go out? (without a comma)
Assess Your Learning
Practice 1. Complete this exercise to practice using coordinating conjunctions.
Practice 2. Combine sentences using coordinating conjunctions.
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