WHETHER AND IF
1. INDIRECT QUESTIONS
WHETHER and IF can both introduce indirect questions:
a. He asked IF/WHETHER I knew Paul;
b. The police officer asked IF/WHETHER I had seen the accident.
In a formal style, WHETHER is usually preferred in a two-part question with OR to emphasize a choice:
a. The travel agent asked WHETHER I wanted to go by air OR by sea.
b. The waiter asked WHETHER I wanted chicken OR fish and chip.
Note the use of WHETHER or NOT to emphasize a choice:
a. He asked WHETHER or NOT I wanted to insure my luggage.
2.PREPOSITIONS
After prepositions, only WHETHER is possible:
a. There was a big argument ABOUT WHETHER we should move to a new house (NOT… about IF we should move);
b. I haven’t settled the question OF WHETHER I’ll go back home.
3.INFINITIVES
WHETHER, but not IF, is used before to-infinitives:
a. They can’t decide WHETHER TO GET married now or wait (NOT they can’t decide if to get married);
b. He wondered WHETHER TO WAIT for them or go on;
c. He couldn’t remember WHETHER TO TURN right or left.
4. SUBJECT, COMPLEMENT AND ADVERBIAL CLAUSES
When a question-word clause is a subject or a complement, WHETHER is normally used:
a. WHETHER WE CAN STAY with my mother is another matter (SUBJECT);
b. The question is WHETHER THE MAN CAN BE TRUSTED (COMPLEMENT).
THE QUESTION IS IF …is also possible, but less common:
The question is IF THE MAN CAN BE TRUSTED.
