Difference between IF and WHETHER

If or whether?

de English Grammar Today

If and whether: indirect questions

We can use if or whether to report indirect yes-no questions and questions with or. If is more common than whether:

Call the bakeries around town and find out if any of them sell raspberry pies.

I rang Peter from the station and asked if I could drop in to see him before going back or if he’d meet me.

We often prefer whether in more formal contexts:

The teachers will be asked whether they would recommend the book to their classes.

[from a business meeting]

John read a letter that he’d written and the board discussed whether it should be mailed.

We prefer whether with or when there is more than one alternative in the indirect question:

After the election, we asked whether the parties should change their leaders, their policies, or both.

To express an alternative, we can use or not with if and whether. With whether we can use or not immediately after whether or in end position. With if we use or not in end position only:

I called Bill to find out whether or not he really did go to Afghanistan.

I called Bill to find out whether he really did go to Afghanistan or not.

I called Bill to find out if he really did go to Afghanistan or not.

We use whether and not if before a to-infinitive, often when we’re referring to future plans or decisions:

I was wondering whether to go for a swim.

Some financial decisions, such as planning a pension, need to be taken as early as possible. Others, such as whether to move house, can probably only be made much later.

Whether not if

We use whether and not if after prepositions:

Later I argued with the doctor about whether I had hit my head, since I couldn’t remember feeling it.

Not: Later I argued with the doctor about if I had hit my head …

The police seemed mainly interested in whether there were any locks on the windows.

Not: The police seemed mainly interested in if there were any locks …

I doubt if, I don’t know whether

We use if or whether to introduce clauses after verbs of doubting:

I don’t know if I can drive. My foot really hurts.

I didn’t prune the rose bush this year so I doubt if we’re going to have many flowers.(‘prune’ means cut back)

We’ll have plenty of photographs to show you but I’m not sure whether we’ll be able to learn very much from them.

See also:

• If
• If: reporting questions

If, whether: typical errors

• We use whether, not if, before to-infinitives:

I don’t know whether to buy the blue one or the red one.

Not: I don’t know if to buy the blue one …

• We use whether, not if, directly before or not:

Can you tell me whether or not you’re interested in the job.

Not: Can you tell me if or not you’re interested …

• We use whether, not if, after prepositions:

[talking about a trip to Australia for a year]

We’re not interested in whether we get great jobs and that kind of thing, we just want to have a good time.

Not: We’re not interested in if we get great jobs and that kind of thing …

Source: http://dictionary.cambridge.org/es/gramatica/gramatica-britanica/if-or-whether