Writing Center

The Seven Deadly Sins of Writing

The Second Deadly Sin: Incorrect Punctuation of Two Independent Clauses

(An independent clause has a subject and a verb and can stand alone as a sentence.)

Good writers know that correct punctuation is important to writing clear sentences.  If you misuse a mark of punctuation, you risk confusing your reader and appearing careless.  Notice how the placement of commas significantly affects the meaning of these sentences:

Mr. Jones, says Ms. Moore, is a boring old fool.
Mr. Jones says Ms. Moore is a boring old fool.

Writers often combine independent clauses in a single compound sentence to emphasize the relationship between ideas.  The punctuation of compound sentences varies depending upon how you connect the clauses. 

The Rules

(a) Separate independent clauses with a comma when using a coordinating
      conjunction (and, but, or, for, nor, so, yet).

(b) Separate independent clauses with a semi-colon when no coordinating
     conjunction is used.

(c) Separate independent clauses with a semi-colon when using a conjunctive adverb
     (e.g., however, therefore, thus, consequently, finally, nevertheless).

Examples of Correct Punctuation, Rule a:

1. We all looked worse than usual, for we had stayed up studying for the exam.
2. This room is unbelievably hot, and I think that I am going to pass out.
3. Monday is a difficult day for me, so I try to prepare as much as possible on Sunday.

Examples of Correct Punctuation, Rule b:

1. We all looked worse than usual; we had stayed up all night studying for the exam.
2. This room is unbelievably hot; I think I am going to pass out.
3. Monday is a difficult day for me; I have three classes and two other commitments.

Examples of Correct Punctuation, Rule c:

1. We all looked worse than usual; however, we were relieved we had studied.
2. The discussion is really interesting; nevertheless, I think I am going to pass out.
3. Monday is a difficult day for me; however, I have figured out how to prepare for it.