Befriending commas and semi-colons

Perhaps no punctuation is misused more in writing than commas.  Semi-colons run a close second.  In the writing classes I’ve taught, many students struggle with when to use commas and semi-colons.  Some use commas way too often while others seldom use them.  Everyone can use a refresher on commas and semi-colons from time to time.  I know I do.

Let’s take a look at an example sentence punctuated three different ways.  Two of the three are correct.  Which ones?

• The man walked briskly down the sidewalk, he was running late for work.
• The man walked briskly down the sidewalk; he was running late for work.
• The man walked briskly down the sidewalk, because he was running late for work.

The last two are correct.  The first one is incorrect because it’s a run-on sentence.  You cannot separate two sentences with only a comma.  The second one is correct because a semi-colon serves to separate two sentences (or independent clauses), yet still ties similar ideas together.  The third one is also correct.  When you use a conjunction (because, and, or, etc.) to separate two complete sentences, then you must use a comma before the conjunction.

Remember that commas are used to separate two sentences tied together with a conjunction that can stand alone.  They are NOT used to separate a dependent and independent clause.  Which of the following is correct?

• The dog barked loudly, and wagged his tail.
• The dog barked loudly and wagged his tail.

The second one is correct.  “Wagged his tail” is a dependent clause (it doesn’t have a subject and verb and cannot stand on its own), so a comma would not be used.  If we changed the sentence to read: “The dog barked loudly, and he wagged his tail,” then we would use a comma.  The second half of the sentence is now independent because it has a subject.

I know grammar and punctuation aren’t the funniest of topics, but they really do help improve writing and communication.  Whether you’re a writer by trade or not having good written communication is important.

What punctuation problems do you encounter most?