A complex sentence is formed by joining an independent clause and a subordinate clause.
A subordinate clause always begins with a subordinating conjunction.
Common subordinating conjunctions are after, although, as, because, before, if, since, until, when, while
When you begin a sentence with a subordinating conjunction, you are beginning the sentence with a subordinate clause. Always put a comma after a subordinate clause. Look at these examples:
Before we eat dinner, you should set the table.
After you pour the drinks, you can wash out the pitcher.
If the dog is hungry, you should feed him.
Since today is Wednesday, we will play softball.
When we sing a song, the dog tries to sing with us.
Use a comma after a subordinate clause when writing a complex sentence.
▶It’s your turn. Place a comma after the subordinate clause in this sentence. Because it is raining we need to take an umbrella. Did you figure out where the subordinate clause ends? Good for you!