whether
Whether is used in reported clauses and conditional clauses.
used in reported clauses
You can use a clause beginning with whether after a reporting verb such as know, ask, or wonder. You use whether when you are mentioning two or more alternatives. You put whether in front of the first alternative, and or in front of the second one.
I don't know whether he's in or out.
I was asked whether I wanted to stay at a hotel or at his home.
When the two alternatives are opposites, you don't need to mention both of them. For example, instead of saying ‘I don’t know whether he's in or out', you can simply say ‘I don’t know whether he's in'.
Lucy wondered whether Rita had been happy.
I asked Professor Gupta whether he agreed.
‘whether...or not’
You can also mention the second alternative using or not. You put or not either at the end of the sentence or immediately after whether.
I didn't know whether to believe him or not.
She didn't ask whether or not we wanted to come.
‘if’
If can be used instead of ‘whether’, especially when the second alternative is not mentioned.
I asked her if I could help her
I rang up to see if I could get seats.
reporting uncertainty
If someone is uncertain about doing a particular thing, or uncertain how to respond to a situation, you can report this using a clause consisting of whether and a to-infinitive.
I've been wondering whether to look for another job.
He didn't know whether to feel glad or sorry that she was leaving.
used in conditional clauses
You can add a clause containing whether and or not to a sentence to indicate that something is true in any of the circumstances you mention.
He's going to buy a house whether he gets married or not.
‘weather’
Do not confuse whether with weather, which is pronounced the same way. If you say that it is raining, windy, hot, or cold, you are talking about the weather.
The wet weather lasted all weekend.
➜ See weather - whether