A period and a comma with FANBOYS are both stop punctuation. However, you cannot use a comma as stop punctuation. When you join two complete thoughts with a comma, you are creating a comma splice, which is an error.
Incorrect: Today is Wednesday, we have art class.
Correct: Today is Wednesday. We have art class. We used a period after each complete thought.
Correct: Today is Wednesday, and we have art class. We used a comma and one of the FANBOYS to join the complete thoughts.
Never join two complete thoughts with a comma. Do not make the mistake of using a comma splice.
It’s your turn. Rewrite this incorrect sentence to eliminate the comma splice: Mary has a dog, Bob has a cat. Did you figure it out? Good for you!