'WHETHER' and 'IF' can be used to introduce alternatives, to express uncertainty and to report questions.
Only ‘whether’ can be used in some cases.
Only ‘if’ can be used in conditional sentences.

• To express alternatives, choices or uncertainty :
  Whether and if they are interchangeable when referring to uncertainty.
  • Alice doesn't know whether/if she'll go to the party on Saturday (or not).
  • Lily wondered if/whether she had unplugged the iron (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.
    • Whether or not we go to the party won't matter to them.
    • I will go for a walk whether or not it rains.
    • 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.

Try an exercise

back to grammar