Nominal clauses include subject clauses, object clauses, predicative clauses and appositive clauses, which are mostly guided by conjunctions that, wh- interrogative words or relative pronouns such as what and what.
1. Subject clause
1) The subject clause acts as the subject in the sentence, and the predicate verb of the sentence is singular in the third person. For example:
What happened outside has nothing to do with us. What happened outside has nothing to do with us.
2) Before the subject clause can not be omitted, it only plays a connecting role. Sometimes in order to keep the sentence balanced, that clause is put at the back, which is the formal subject. For example:
It is estimated that it takes more than 1000 miles to and from Mars.
It is estimated that it will take more than a year to fly to Mars and return.
2. The object clause acts as the object in the sentence. For example:
I don't know where the sound came from. I don't know where the sound came from.
Don't be satisfied with what you have achieved. Don't be satisfied with what you have achieved.
When the clause is placed in the copula verbs be, look, remain, seem, etc. It constitutes an predicative clause. For example:
The trouble is that I have lost his address. The trouble is that I lost his address.
It seems to be snowing. It looks like snow.
4. appositive clauses
1) appositive clause is a further explanation of appositive noun head. Common nouns that can be used with appositive clauses are: idea, fact, news, believe, hope,
Evidence, opinion, question, truth, answer, suggestion, theory, decision,
Discovery, problem, thought, certainty, possibility, provided that, in
Reasons, exceptions, spices of facts, preventive measures, etc.
The news that he passed the exam is exciting. The news that he passed the exam is exciting.
I lent her the book on condition that she return it before.
Sunday. I lent her the book on condition that she would return it to me before Sunday.
2) The difference between appositive clauses and attributive clauses is that attributive clauses modify and restrict antecedents, and appositive clauses explain the specific content of the head word; That acts as a relative pronoun in the attributive clause, but does not act as a conjunction in the appositive clause, such as:
The facts we talked about are very important. The situation we are discussing is very important.
The fact that he succeeded in the experiment is gratifying.
Everyone. The fact that he succeeded in the experiment made everyone happy.
5. The difference between what and if in noun clauses.
If is generally only used to guide the object clause, while when can guide whether the nominal clause includes the object clause.
1) The subject clause and predicative clause guided by the conjunction "whether" cannot be replaced by "if".
Whether he will attend the meeting is uncertain.
2) In the object clause, when often collocated with or not, you can say whether, instead of if or not.
I don't care whether she will attend the meeting or not. I don't care whether she comes to the meeting or not.
3) When can be used after prepositions or before infinitives, but if is not.
She doesn't know whether to get married now or wait. She doesn't know whether to get married now or wait.
4) After some verbs (such as discuss), you can only use what instead of if.
We discussed where we should continue to climb the mountain. We discussed whether to continue climbing.