See The Sentence for definitions of sentence, clause, and dependent clause.
A sentence which contains just one clause is called a simple sentence.
A sentence which contains one independent clause and one or more dependent clauses is called a complex sentence. (Dependent clauses are also called subordinate clauses.)
There are three basic types of dependent clauses: adjective clauses, adverb clauses, and noun clauses. (Adjective clauses are also called relative clauses.)
A. Adverb clauses show relationships such as time, cause and effect, contrast, and condition. (See Conditional Sentences for more information on this type of adverb clause.)
B. A sentence which contains one adverb clause and one independent clause is the result of combining two clauses which have one of the relationships above. You can combine two independent clauses to make one sentence which contains an adverb clause by following these steps:
1. You must have two clauses which have one of the relationships in A above:
Billy couldn�t swim.
He jumped off the pier. (contrast)
2. Add a subordinating conjunction to the beginning of the clause you want to make dependent:
Although Billy couldn�t swim
He jumped off the pier.
3. Place the two clauses next to each other. Usually, the order of the clauses is not important. When the adverb clause precedes the independent clause, the two clauses are usually separated by a comma:
Although Billy couldn�t swim, he jumped off the pier.
When the independent clause precedes the adverb clause, there is usually no comma:
Billy jumped off the pier although he couldn�t swim.
C. The subordinators in adverb clauses are called subordinating conjunctions. They cannot be omitted. They cannot be subjects. Here are some of the subordinating conjunctions:
Time: after, before, when, while, as, by the time, whenever, since, until, as soon as, once, as long as
Cause and effect: because, since, now that, as, as long as, inasmuch as, so (that), in order that
Contrast: although, even though, though, whereas, while
Condition: if, unless, only if, whether or not, even if, providing (that), provided (that), in case, in the event (that). See Conditional Sentences.
D. Here are some examples of sentences which contain one adverb clause (underlined) and one independent clause. The two sentences in each pair have the same meaning:
After he took lessons, George could swim well.
George could swim well after he took lessons.
Because he couldn�t swim, Billy drowned.
Billy drowned because he couldn�t swim.
Although he isn�t interested in food, Fred works as a cook.
Fred works as a cook although he isn�t interested in food.
If you want to write well, you must practice.
You must practice if you want to write well.