A complex sentence combines a subordinate clause with an independent clause.
The words after and before are subordinate clause words. We can use those words to begin a subordinate clause.
Here is a complex sentence that begins with the subordinate clause word after:
After I eat dinner, I will wash the dishes.
After I eat dinner makes no sense all by itself. That’s why we call it a subordinate clause.
The second half of the sentence is the independent clause: I will wash the dishes.
Any sentence with a subordinate clause must also have an independent clause to make it a complete sentence.
If we start with a subordinate clause, we use a comma between the two clauses.
After I eat dinner, I will wash the dishes.
Now look at this sentence: I will wash the dishes after I eat dinner.
This time, we started with the independent clause – I will wash the dishes.
The subordinate clause – after I eat dinner– is at the end of the sentence.
If you look closely, you can see that we did not use a comma this time.
Here are more examples of complex sentences using after and before.
Notice that each of these sentences has no comma because the independent clause comes before the subordinate clause.
Mom will go shopping after she finishes writing a grocery list.
Dad has to put gas in the car before he can drive us to practice.
I saw a rainbow in the sky after the storm stopped.
You need to pump up your bike tires before you go for a ride.
If you begin a complex sentence with the independent clause, do NOT put a comma between the clauses. Only use a comma in a complex sentence when the sentence begins with a subordinate clause word.