WHETHER - IF

• To express alternatives :
  • Alice doesn't know whether/if she'll go to the party on Saturday (or not).
  • She hasn't decided whether/if she'll accept the invitation (or not).
    
    
• To report a question :
  • Are you going to the party?
    - She asked me whether/if I was going to the party (or not).
    - He said he didn't know whether/if he was going to accept the offer (or not).
    
    
• Only WHETHER can be used in the following cases:
  
  
  • When followed by an infinitive :
    • I don't know whether to go to the party or not. (NOT: if to go)
    • I don't know whether to accept the offer or not.
      
      
  • After prepositions :
    • I'm not sure I can join you. It depends on whether I get home early or not.
    • We need to talk about whether to move house.
      
      
  • When whether begins a clause which is the subject of a sentence.
    • Whether we go to the party or to the cinema makes no difference to me.
    • Whether we take the car or go by taxi is all the same to me.
      
      
  • When followed directly by 'or not'
    • I'll be happy whether or not we go to the party.
    • I don't know whether or not Alex received an invitation.
      
      
    With whether we can use 'or not'  immediately after whether, or at the end of the sentence.
    With if we use 'or not' in end position only.
    
    
    • I called Angela to find out whether or not she was going to the party.
    • I called Angela to find out whether she was going to the party or not.
    • I called Angela to find out if she was going to the party or not.
      
      
• Only IF can be used in conditional sentences:
  • What would Max do if he lost his job?
  • I'll come to your party if you invite me.
  • If I had missed the train, I wouldn't have arrived on time.
    
    
• GENERAL RULE:
  • Use IF to introduce a condition.
  • Use WHETHER for choices and alternatives.

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