A dependent clause also called a subordinate clause is a group of words that forms part of a sentence. It has a subject and a verb, but does not express a complete thought, making it a dependent clause that cannot stand independently as a complete sentence. The dependent/subordinate clause is joined to an independent clause or main clause, to which it adds more information. Together, they form a complete sentence. Each subordinate clause begins with a subordinating conjunction such as because, since, unless, and even though. It is this subordinate conjunction that makes a dependent clause subordinate to the independent clause. Most subordinate clauses are adverbial clauses.
When a subordinate clause is one of two clauses in a sentence, the other clause has to be the main clause as a sentence cannot have only two subordinate clauses. The subordinate clause usually comes after the main clause. However, it can come in front of the main clause to draw attention to its content before the main clause. The third position that a subordinate clause can take in a sentence is in the middle.
It will be noticed that commas are used when the subordinate clause comes at the beginning or in the middle of a sentence. A comma is used after a subordinate clause when the subordinate clause is followed by the main clause, while a comma is used before and after the subordinate clause when the clause is in the middle of the sentence. When the main clause is followed by the subordinate clause, no comma is used.
Each of the following example sentences shows a subordinate clause (boldfaced) that is joined to a main clause. Both clauses together form a complete sentence.