Preparing for the 'oposiciones': if/whether in indirect questions

Shall we use whether or if in indirect questions?

Both mean 'si' and, in most cases, you can use one or the other, with no difference in meaning, though it can be said that if is more colloquial than whether:

I asked her if/whether she loved me - le pregunté si me quería
I'm not sure if/whether I can go to your birthday party next Friday - no estoy segura si puedo ir a tu fiesta de cumpleaños el próximo viernes 
I wonder if/whether I should tell the boss - me pregunto si debería decírselo al jefe.

When the alternative with or/or not is explicitly expressed, whether is generally preferred, though if is often acceptable too:

She didn't know whether/if she was pregnant or not - no sabía si estaba o no embarazada
We haven't decided yet whether/if we're going to the beach or to the country - no hemos decidido todavía si vamos a ir a la playa o al campo.

However, only whether should be used in the following cases:

a)  before an infinitive:

I don't know whether to go to Rome or to Venice - no sé si ir a Roma o a Venecia

b) after a preposition:

It depends on whether we can get the money to buy it - depende de si podemos conseguir el dinero para hacerlo

c) when it is followed  directly by or not:

I don't care whether or not he plays the guitar - no me importa si toca o no la guitarra (more usually I don't care whether/if he plays the guitar or not)

d) when the indirect interrogative clause is in the subject position:

Whether you marry her or not is none of my business - que te cases o no con ella no es asunto mío.

e) in the expression, fixed by use, whether you like it or not:

You must go to school whether you like it or not -

Note

In conditional sentences, of course, you always use if, never whether.

EXERCISE

Fill in the gaps with if or whether as appropriate; if both are acceptable, put the one which is more usual first:

1.- I can't decide ...........to buy a car or a bike.
2.- I'd like to know...........your mother is finally coming for the weekend or not.
3.- I don't know yet .......she will come or not.
4.- It depends on ....... she can find a cheap flight.
5.- You have to pay taxes..........you like it or not.
6.- I don't care ......... he's rich or poor. I love him and I will marry him.
7.- There was a big argument about .......the Prime Minister should resign.
8.- ..........they will pay  me or not I am not so sure.
9.- Norman asked Elsie .........she'd like to go to the cinema.
10.- In our next meeting, it will be discussed ...... it would be better to stop investing in land property.
11.- I'm not sure ..........I'll have time to go to the hairdresser's.
12.- Let me know as soon as possible...........you will be able to attend the conference.
13.- I doubt............she will recognize me after such a long time.
14.- Nobody knew  .....  or not the technique was going to work.

KEY

1.- whether; 2.- whether/if; 3.- whether/if; 4.- whether; 5.- whether; 6.- whether/if; 7.- whether; 8.- Whether; 9.- if/whether; 10.- whether; 11.- if/whether; 12.- whether/if; 13.- if/whether; 14.- whether.