Commas With Independent Clauses Joined By a Conjunction

1. A conjunction is a word used to join sentences: and, but, or, for, nor, so or yet.
2. If a conjunction joins two or more independent clauses to form a compound sentence, place a comma after the first clause.
• I went to bed late last night, so I feel so sleepy right now.
• The country’s economy has shown signs of improvement, but many people are still jobless.
• Sam forgot his house keys this morning, and now he can’t enter the house.

Note:

If an independent clause is joined without a conjunction, they are separated by a semicolon instead of a comma.

• I went to bed late last night; I feel so sleepy right now.
• The country’s economy has shown signs of improvement; however, many people are still jobless.
• Sam forgot his house keys this morning; now he can’t enter the house.