Commas and Clauses

David Powers King's blog post about commas had me thanking the universe another writer was as crazy about commas as I am. (Crazy in a good way, David.) So I felt inspired to share the number one comma mistake I see in writing and how to correct it.

This mistake I see involves separating a "two part" sentence--the two parts involving either independent or dependent clauses.

What's the difference between the two? On its own, an independent clause can be a complete sentence, whereas a dependent clause cannot.

So let's dissect the following sentence:

•  Mary had a little lamb and ate him for dinner. (Yes, I had a stroke of genius with this one.)

"Mary had a little lamb" is an independent clause because it has a subject and a verb, therefore making it a complete sentence in its own right.

"ate him for dinner" is a dependent clause because it can't stand alone as its own sentence.

When you have a sentence in "independent clause, dependent clause order," you DON'T NEED A COMMA to separate the clauses. So the example I have above is punctuated correctly. (EDIT: The exception to this rule is in cases where you have extreme contrast between the clauses, like when the dependent clause is preceded by "but," "although," or "except"--then you'd use a comma to separate the clauses.)

However, when you have TWO independent clauses in a sentence, they need separation by a comma.

For example:

• Mary had a little lamb, and she ate him for dinner.

The addition of "she" gave the second half of the sentence its subject, therefore making it an independent clause and justifying the dividing comma.

HOWEVER, exceptions to "two independent clause comma" rule may be granted for sentences short enough that a comma would muddle their appearance. If I had the above example sentence in my novel (please let that never happen!), I probably wouldn't use the comma because that sentence is so brief.

So now let's flop things around. What if we started a sentence with a dependent clause followed by an independent clause? In all cases, you'd need a comma to separate the clauses. Remember, dependent clauses depend upon the other part of the sentence for complete meaning and can't stand alone. Here are some examples:

• Eating him for dinner, Mary had a little lamb.
• If Mary had a little lamb, she would eat him for dinner.
• When Mary had a little lamb, she ate him for dinner.
• As Mary had a little lamb, she ate him for dinner. 
• Because Mary had a little lamb, she ate him for dinner.

There is no exception to this rule. No matter how brief the sentence, you must use a comma.

Hopefully this helps in your quest to conquer the confusing comma. May the grammar gods be with you!