IF / WHETHER

If puede indicar hipótesis, suposición If you come, bring me the money.
If I had money I would buy the house.
I would go if he invited me.
Tell me if your mother marries Robert.
If she comes show her my room.
If this is true, then I will not go.
Act as if you were intelligent.

Cuando tenemos alternativas entre varias cosas, o podemos elegir, empleamos whether: I didn’t know whether to go by car or by train.
I don’t know whether I should marry Peter or Paul.
Si existe duda, empleamos whether: He didn’t say whether he would come.
I am not sure whether she will come.
You will have to do it whether you like it or not.
Los nativos incultos se arman un lío y acaban empleando if siempre, con lo cual enseñan el plumero de su baja cultura.

En ambos casos, en castellano es “si”.

Y para rematar la faena, si decimos: Tell me if this is correct (si no lo es no me digas nada). Tell me whether this is correct (avísame si hay algún error).