A complex sentence combines an independent clause and a subordinate clause. An independent clause is a simple sentence that stands all by itself. A subordinate clause cannot stand alone; it must always be joined to an independent clause.
Independent clause: I will do my homework.
Subordinate clause: After we eat dinner.
Notice that the independent clause is a complete sentence. The subordinate clause does not make sense by itself. We wonder, what happens after we eat dinner? When we combine the two clauses, we get a complex sentence: After we eat dinner, I will do my homework. Now the subordinate clause makes sense because we joined it to the independent clause.
Notice the comma after the subordinate clause. Whenever you begin a complex sentence with a subordinate clause, you must put a comma after the subordinate clause.
Here is one more example: While we eat dinner, we can watch a movie.
Use a comma after a subordinate clause in a complex sentence.
It’s your turn. Find the place in this sentence where the subordinate clause ends and the independent clause begins. Put a comma after the subordinate clause. Before you go to school you should feed the dog. Did you figure it out? Good for you!