A complex sentence is made up of two clauses: an independent clause and a subordinate clause.
An independent clause is the main idea of the sentence and is strong enough to stand alone.
The dog can stay in the yard.
This independent clause makes sense all by itself.
Here is a subordinate clause: while I wash the kitchen floor.
This clause begins with a subordinate clause word and cannot stand alone. This clause makes no sense by itself because the reader wonders what will happen while I wash the kitchen floor.
When we put these two clauses together, we make a complex sentence.
The dog can stay in the yard while I wash the kitchen floor.
The independent clause – The dog can stay in the yard – is the idea being emphasized in the sentence.
Washing the kitchen floor is less important so we made that the subordinate clause – while I wash the floor.
If we want to emphasize that we are washing the floor, we can make that the independent clause, like this:
I will wash the floor while the dog stays in the yard.
Now the dog in the yard is less important because that clause begins with the subordinate clause word while.
Here is another complex sentence. Can you tell which idea in the sentence is more important?
Look for the independent clause. That will be the more important idea.
After the snow stops, I can clear the driveway.
Did you notice that the more important idea is I can clear the driveway?
If we want to emphasize the stopping of the snow, we can write the sentence like this:
The snow must stop before I can clear the driveway.
The clause about the snow is now the more important independent clause.
We can switch the order of the clauses in a complex sentence, but switching the order of the clauses changes the meaning of the sentence. The independent clause is always the more important clause in a complex sentence.