Complex Sentences

Complex sentence contains one independent clause and one or more dependent clauses.

An independent clause is a word group that has a subject and a verb and expresses a complete thought. It can stand alone as a sentence. A dependent clause also has a subject and a verb, but it does not express a complete thought. It can't be a sentence on its own.

The complex sentence is formed with one of the three various dependent clauses — noun clause, adjective clause, and adverb clause.

[1] With noun clauses

A noun clause is used as a noun within a sentence. It begins with a subordinator like how, however, if, that, what, whatever, when, where, whether, which, whichever, who, whoever, whom, whomever, whose, why, etc.

• That they won't be late is our hope. [subject]
• He says that he is a teacher. [Direct object]
• He told whoever is interested in investing the news. [Indirect object]
• We judge a man by what he does. [Object of preposition]
• Freedom and justice are what we want. [Subject complement]
• You can call me what you like. [Object complement]
• He reached the conclusion that it was wise to stay out of politics. [Appositive]
• He is happy that he has passed the exam. [Adjective complement /Adverbs]

[2] With adjective clauses

The adjective clause is placed next to the noun or pronoun that it modifies.

• Vutha, who is my brother, is a sleepwalker.
• The man whom you see is a teacher.
• The dog that kept me awake all night lived next door.
• A marriage which is based on trust succeeds.

[3] With adverb clauses

The adverb clause may be placed at the beginning of or the end of the sentence. The difference is that a comma is needed when the dependent clause is placed before the independent clause at the beginning of the sentences.

Therefore, the pattern is either:  
Independent clause + Dependent clause (IC + DC.), or 
Dependent clause + comma + Independent clause (DC, IC.).

• Although they work very hard, they earn very little.
• If you are drunk, don't drive.
• She skipped lunch because she was so busy.
• Since my alarm clock did not ring, I overslept.
• I will call you after I get home.