Here are Rules 12 through 16.
Rule 12. Use a comma to separate two strong clauses joined by a coordinating conjunction--and, or, but, for, nor. You can omit the comma if the clauses are both short.
I have painted the entire house, but he is still working on sanding the doors.
I paint and he writes.
Rule 13. Use the comma to separate two sentences if it will help avoid confusion.
I chose the colors red and green, and blue was his first choice.
Rule 14. A comma splice is an error caused by joining two strong clauses with only a comma instead of separating the clauses with a conjunction, a semicolon, or a period. A run-on sentence, which is incorrect, is created by joining two strong clauses without any punctuation.
Time flies when we are having fun, we are always having fun. (Comma splice)
Time flies when we are having fun we are always having fun. (Run-on sentence)
Time flies when we are having fun; we are always having fun.OR
Time flies when we are having fun, and we are always having fun. (Comma is optional because both strong clauses are short.)
Time flies when we are having fun. We are always having fun.
Rule 15. If the subject does not appear in front of the second verb, do not use a comma.
He thought quickly but still did not answer correctly.
Rule 16. Use commas to introduce or interrupt direct quotations shorter than three lines.
He actually said, "I do not care."
"Why," I asked, "do you always forget to do it?"
See previous rules as follows:
Part III is here.
Part II is here.
Part I is here.
Colleen Degnan Johnson
Fantasy Face Painting