Hello, fellas. How is life today? In this session we are going to learn noun clauses beginning with if or whether. According to Betty Schrampfer Azar, a noun clause is a clause used as a subject or an object of a sentence.
When a noun clause begins with if or whether, it means that the clause is changed from a yes/no question. There is no difference in meaning between noun clauses using if and whether. However, whether is more formal and if is more common in speaking.
1. Yes/No Question: Will he go?
a) They know whether he will go.
b) They know if he will go.
2. Yes/No Question: Does she understand the lesson?
a) We wonder whether she understands the lesson.
b) We wonder if she understands the lesson.
The expression or not may be added in noun clauses.
1. We wonder whether or not she understands the lesson.
2. We wonder whether she understands the lesson or not.
3. We wonder if she understands the lesson or not.
4. Whether she understands the lesson or not is unimportant to us.
Betty Schrampfer Azar, Understanding and Using English Grammar: Third Edition