A subordinate clause must be attached to an independent clause to make a complete sentence. If the sentence begins with the subordinate clause, you must place a comma after the subordinate clause before writing the independent clause.
Look at these examples of a complex sentence. Each sentence begins with a subordinate clause followed by a comma and then an independent clause.
If it rains tomorrow, our baseball game will be postponed.
While I was taking a nap, my friend rang the doorbell.
After I do my homework, I will go to the mall.
A complex sentence combines a subordinate clause and an independent clause. You can change the order of the clauses. Begin with the independent clause and put the subordinate clause after. When you order the clauses in this way, you do not put a comma between the clauses. Look at these examples:
Our baseball game will be postponed if if rains tomorrow.
My friend rang the doorbell while I was taking a nap.
I will go to the mall after I do my homework.
A complex sentence is made by joining a subordinate clause and an independent clause. If you begin a complex sentence with the subordinate clause, put a comma between the two clauses. No comma is needed if you begin a complex sentence with the independent clause.
It’s your turn. Look at this sentence. Decide if it needs a comma between the clauses. Unless the temperature gets warmer our garden will freeze. Did you figure out that the sentence begins with a subordinate clause? Do you know what to do? Good for you!