A noun clause serves the same purpose as a noun. It can be the subject or object of a verb. It can also be the object of a preposition. Noun clauses are usually introduced by the subordinating conjunctions that, if and whether. Question words like what, how, when etc., can also be used to introduce noun clauses.
Read the examples given below.
That he is a diligent boy is known to everybody.
Can you identify the subject?
What is known to everybody?
The answer to this question is the subject of the sentence
– that he is a diligent boy.
Since this clause serves as the subject of the verb ‘is known’, it is considered as a noun clause.
Note that when the subject is a noun clause we are more likely to write the sentence with a preparatory it.
That he is a diligent boy is known to everybody. à It is known to everybody that he is a diligent boy.
Another example is given below.
Picasso was a great artist. Nobody can challenge this fact.
What cannot be challenged? The fact that Picasso was a great artist
Replace the question word with the that-clause and we will get the following complex sentence:
The fact that Picasso was a great artist cannot be challenged.
More examples of noun clauses are given below.
He is an honest boy. Everybody knows it.
Everybody knows that he is an honest boy.
Here the noun clause ‘that he is an honest boy’ is the object of the verb knows.
Why he is late? Ask him.
Ask him why he is late.
Here the noun clause ‘why he is late’ is the direct object of the verb ask.
Noun clauses are important devices because they help us to combine two or more simple sentences into a single complex sentence.