Noun Clauses: Tutorial

A noun clause is a dependent clause that begins with a question word and is used as a subject or an object of a sentence.
  
Form
Wh-question words       if (yes/ no questions)
what       that
when       whether
where
why
who
whom
which
whose
how
  
Usage Wh-question Words + S + V +.....  (subject position)
  
What I discovered was exciting.
  
........+ Wh-question Words + S + V+  (object position)
  
I realized who he was.
  
If/whether is used in response to yes/no questions.
  
Is he home?
I don't know whether/if he is home.
  
That can be omitted if it is used as the object pronoun in a noun clause.
  
That he is late worries me.  (subject position)
  
I think (that) he is lost. (object position)
I think he is lost .
  
A noun clause does not have a question word order even though it starts with a question word. The verbs do, does, and did are not used in noun clauses.
  
In a sentence, the subject of a noun clause always takes a singular verb.
  
S V
Why  they refused to pay the bill is a mystery.
 
Noun Clauses - Subjectives in Noun Clauses - Examples