So far you have studied how to put two sentences together by coordinating them, that is keeping them equal. Chapter Four explores subordination which is putting sentences together by turning one of them into a dependent clause. A dependent clause is still a clause; it has a subject and a verb, but does NOT make sense by itself. A dependent clause depends on another independent clause in order to make sense.
Dependent clauses are created by using subordinating conjunctions to join the two sentences. The subordinating conjunction can be added at either the beginning of the first sentence or between the two sentences you are joining. This sentence pattern of one independent clause and one or more dependent clauses is called a complex sentence. Punctuating complex sentences is fairly simple. If the dependent clause begins the sentence then a comma is used at the end of the dependent clause. If the independent clause begins the sentence, then no comma is necessary. Using subordination and coordination helps your writing by giving it variety and interest in the sentence structures.