As you progress in the study of grammar you are gradually taught to combine two or more simple sentences into a single complex sentence. The main purpose of doing so is to make the sentence crisp. But unless you know the proper rules you are not in a position to combine two or more simple sentences into a complex one.
The rules which are given below should always be followed by you as you try to combine two or more complex sentences. In the first place it is recommended that you convert one simple sentence into a principal clause and the other simple sentences into sub-ordinate clauses.
When you are using a noun clause in a complex sentence it does the job of a noun in the sentence. In fact the noun clause in a sentence can act as a subject or an object of the verb which is present in the principal clause.
Some of the examples are as follows:
Simple Sentences: A good environment is essential for happiness in life. He believes this.
Complex Sentence: He believes that a good environment is essential for happiness in life.
Simple Sentences: Could he depend on the guide? The traveler did not know.
Complex Sentence: The traveler did not know whether he could depend on the guide.
Simple Sentences: He is bent on mischief. It is known to everybody.
Complex Sentence: That he is bent on mischief is known to everybody.
All these are basically examples of using noun clauses in a complex sentence; in these sentences the noun clause does the job of a noun. Moreover if you notice carefully you will see that in a complex sentence you cannot get an independent part of the sentence. Every part of the sentence is dependent on each other unlike the simple sentences.
In case of complex sentences you can also use the adjective clause which does the work of an adjective that is it modifies or qualifies either a noun or a pronoun in the main clause or in the principal clause.
The examples are as follows:
Simple Sentences: The slave had to fight with a hungry lion. The lion was kept in a cage.
Complex Sentence: The slave had to fight with a hungry lion which was kept in a cage.
Simple Sentences: He is a prince. Trouble had driven him from home.
Complex Sentence: He is a prince whom trouble had driven from home.
Even in these sentences if you look carefully you will see that the adjective clause which is part of the subordinate clause qualifies the noun or the pronoun which is present in the principal clause of the sentence. In the first sentence the noun “lion” is described and in the second sentence more is told about the pronoun “he”.
You can also use adverb clauses while you are joining two or more simple sentences into a complex sentence. The function of an adverb clause is qualifying a verb, an adjective or sometimes which is present in the main clause. For example:
Simple Sentences: He got the first prize. He was happy.
Complex Sentence: He was happy when he got the first prize.