We use a comma ( , ) in writing to show a place for a pause or a separation. This week we are talking about commas used within certain sentence structures.
First of all, it is important to remember that a clause is a group of words with a subject and a verb. A clause can be independent or subordinate (dependent).
In post 146, we talked about a compound sentence where two complete thoughts are joined by a comma and one of the FANBOYS (the coordinating conjunctions).
Today we will talk about a complex sentence. In a complex sentence, one part of the sentence is a complete thought (an independent clause) and the other part of the sentence is an incomplete thought (a subordinate clause.) The subordinate clause is of less importance in the sentence. The subordinate clause begins with a subordinating conjunction (also called a subordinate clause word.)
Here are some subordinating conjunctions: if, when, since, because, while, after, before. You use one of these words to start a subordinate clause. A subordinate clause cannot stand alone; it must be attached to an independent clause.
When you begin a sentence with a subordinate clause, you must put a comma after the clause before you add the independent clause. Look at these examples. Each complex sentence begins with a subordinate clause word:
If you have time, please help me wash my car.
When we get done with the car, we can go to the park.
Since it is a hot day, we should go swimming.
Because I left my towel at home, I need to borrow one of yours.
While we swim, we can keep cool.
After we swim, we should get ice cream.
Before we go home, I need to buy gas.
Look closely at these sentences.
Each sentence begins with a subordinate clause word, which means we started the sentence with a subordinate clause. You must put a comma after the subordinate clause before adding the independent clause.
You can also begin a sentence with an independent clause and tack the subordinate clause onto the end of the sentence, like this: I need to buy gas before we go home.
The subordinate clause before we go home begins with the subordinate clause word before. We don’t use a comma here.
If the independent clause goes first, do not use a comma to separate the two clauses.
Use a comma after a subordinate clause but not after an independent clause. Never put a comma before a subordinate clause word.