Noun (or nominal) clauses are clauses whose function within the sentence is equivalent to that of a noun or noun phrase. For example, the noun clauses in the following sentences have the same functions as the corresponding noun phrase:
Whether he comes or not/The question is important (subject)
I don't know whether he will come or not/the answer (direct object)
The problem is whether John's father will come or not/John's father (subject complement)
It all depends on whether or not he comes/him (prepositional complement)
The various kinds of structures that can occur as noun clauses are as follows:
that clauses
I knew that he would come.
interrogative clauses
I don't know what made him do it.
nominal relative clauses
Whoever breaks the law must be punished.
infinitive clauses
He likes to be admired.
-ing participle clauses
He enjoys teasing me.
Finite and non-finite clauses functioning as verb complements are discussed in 3.1-15.