A complex sentence contains an independent clause and a dependent clause. Independent clauses can function as a complete sentence, while dependent clauses cannot. A dependent clause in a complex sentence must contain a subordinating conjunction. There are two ways to structure a complex sentence: beginning with the independent clause and beginning with the dependent clause.
A complex sentence that begins with its independent clause requires a subordinating conjunction but not a comma.
In the above example, the dependent clause contains the subordinating conjunction after.
A complex sentence that begins with its dependent clause requires both a subordinating conjunction and a comma. The subordinating conjunction will appear at the beginning of the dependent clause, and the comma will separate the two clauses.
In the above example, the comma separates the dependent clause After he did his homework from the independent clause Nick watched cartoons.
There are many subordinating conjunctions. Here is a list of some common ones:
The subordinating conjunction determines what the relationship is between the independent clause and the dependent clause.
Notice how in the examples above, the subordinating conjunction changes the meaning of the sentence.