This is another area that I frequently see some serious comma whoring going on. People are tossing commas before—and occasionally after, but that is another problem altogether—every conjunction they write.
This behavior is not okay. Please stop doing it.
Overuse of commas depletes the ozone, and you don’t want to be responsible for polar bears losing their habitat do you?
First, a conjunction is a little word that connects two clauses. These little words can be remembered as FANBOYS.
For, And, Nor, But, Or, Yet, So
You only put a comma before the conjunction when the both halves are COMPLETE sentences, meaning they contain a subject, verb, and express a complete thought.In other words, they can be read separate of each other and still make sense.
When one side is incomplete, there is NO comma.
When one side depends on the other, there is NO comma.
Here are some examples:
He got up and walked to the fridge. <- see, no comma. The right side is missing a subject, so it is not a complete clause. If you read the clauses separately, you would get: He got up. Walked to the fridge. See it now?
He got up, and he walked to the fridge <-see, there is a comma. Both sides have a subject. Read them separately now: He got up. He walked to the fridge. See how they both make sense on their own.
I went to the store, and I bought milk and cookies.<-comma
The cookies were good, so I went back and got more. <-comma
I stood and dropped my pants. <-no comma
Pissed, I flipped him off and ran him over with my car. <-no comma
Now there are a few exceptions to the rules. If you are trying to show a contrast, then you may use a comma despite both clauses not being complete.
Example: I love red, but hate blue. <-see the contrast?
And if the two halves of the sentence are balanced you may leave out the comma.
Example: I love white horses and I wish I was a sloth. <- See? It’s balanced so no comma.
There is a whole rule set for the wonderful wannabe conjunction ‘then,’ but I will tackle that in another post.