A dependent clause is a complete thought that is not a complete sentence. It has a subject and a verb and is usually preceded by a subordinating conjunction. A dependent clause differs from an independent clause because an independent clause is a complete sentence on its own, whereas a dependent clause is a sentence fragment on its own. A definition of a dependent clause is: "although she reads." A dependent clause can become part of a simple sentence if it loses the subordinating conjunction. For example, "although she reads" becomes "she reads." Or, it can be connected to an independent clause. For example, "although she reads" becomes "Although she reads, she doesn't like it."
A complex sentence is one independent clause and one dependent clause connected by a subordinating conjunction. The conjunction is often at the beginning of the sentence and a comma separates both clauses. An example of a complex sentence is: "Although she was happy, she didn't want to leave." The subordinating conjunction is "although." The dependent clause is "although she was happy" and the independent clause is "she didn't want to leave."
According to the textbook "Grammar for Writing," subordinating conjunctions can explain time, place, cause, comparison, condition or purpose. Examples include "after, as long as, however, although, even though, in order that, where and because." Often, complex sentences begin with words such as "because" or "since." For example, "Because she failed her test, she could not go to the dance."
A student who does not understand the difference between dependent clauses and independent clauses may often write in sentence fragments, say Ruth Townsend Story and Cathleen F. Greenwood, authors of "Grammar Lessons You'll Love to Teach." School lessons should focus on teaching students how to identify the various clauses, define the terminology and understand how to write these types of sentences. A student who can write a complex sentence will be much more advanced in her writing.