Whether / if

If and whether, of course, always imply uncertainty. You can generally use if or whether when you are reporting yes/no questions. It doesn't matter which you choose:

"Can you take care of Tommy for me?
~ I don't know yet whether / if I shall be able to look after Tommy during the Easter holidays or not."

"Is James still around?
I wondered whether / if James had left the country as I hadn't seen him for some time."


However, after prepositions, before to-infintives, in 'whether…or…' constructions and whenever we start a sentence with the conjuntion, we HAVE to use whether:

"Whether I'll get there in time for Sarah's lecture, I don't know."

"I can't make up my mind whether to buy some new clothes now or wait until the sales.. "

"There was a lot of discussion about whether Ian should have his tongue pierced or not."

"Whether we go by bus or by train doesn't really matter. It's bound to be a slow journey."

"I'm going to spend all of granny's money on a new kitchen whether you like it or not!"


TO SUMMARISE:

1. When both choices are given, we generally use whether rather than if:

I don't know whether she's coming or not.
(It would be possible to use if here, but less common.)

2. Before an infinitive with 'to' we use whether:

I don't know whether to accept their offer or not.
(If would not be used here.)

3. We use whether after a preposition:

It's a question of whether we can agree on everything.
(If would not be used here.)

4. Both whether and if can be used in indirect speech to introduce a yes\no question:

Did they say whether\if they were going to be late?

5. After some verbs, we use whether:

I doubt whether they'll make it.
We discussed whether it was the correct decision.

Hello Candy

Richard summarized the differences between "if" and "whether" in an excellent way.
I'd like to add three things more to his summaries.
[1] "Whether" clauses can follow "a question" as an appositive clause
EX-1 Candy raised a question whether there is any difference between if and whether.
[2] "Whether" clauses can be used as an indirect question for asking listener's choice beside an Yes/No answer.
EX-2 She asked him whether it was his turn or hers.
[3] We can use "whether" in a indirect question that directly leads "or not".
EX-3 I wonder whether or not my ex-wife is still alive.
Beside these special characteristics (including what Richard already explained about), "if" clauses and "whether" clauses are almost inter-exchangeable though the latter is high in the degree of formality.

The verbs that people use more often with "whether" than "if" are "inspect", "discuss", "ponder", "argue" and "inquire". Please refer the Google survey results below given.

verbs more often combine with
suspect if/whether 105,000/5,090 ; think if/whether 2,410,000/74,600 ; see if/whether 36,300,000/3,650,000 ;
hear if/whether 292,000/84,000 ; know if/whether 24,600,000/6,170,000 ; wonder if/whether 8,720,000/1,510,000;
ask if/whether 3,690,000/1,600,000 ; query if/whether 147,000/45,200 ; study if/whether 555,400/216,000 ;
doubt if/whether 886,000/697,000

verbs more often combine with
investigate if/whether 208,000/1,050,000 ; discuss if/whether 85,500/544,000 ; ponder if/whether 22,000/40,100
argue if/whether 43,500/64,700; inquire if/whether 141,000/177,000

paco

Hello Candy

Yes, I am from Japan. I have learned English for decades but still am very poor at English. I believe you will get much more proficient in English in a few years as long as you continute the study as you are doing now.

paco