Difference between 'if' and 'whether'

[Unregistered]

hello
would you please kindly explain what is the difference between 'if' and 'whether'. which one is more/less formal, in which case either of them are used, etc.

thank you in advance

 

[David L.]

'If' and 'whether' are more or less interchangeable in sentences like," I'll see if/whether he left a phone number" .
'whether' is generally regarded as more formal and suitable for written use. But, although 'if' and 'whethe'r are often interchangeable, one distinction is that 'if' is also used in conditional constructions and 'whether' in expressing an alternative or possibility. Thus : "Tell me if you’re going to be in town next week' could be strictly interpreted as 'you need not reply if you are not going to be in town,' whereas : "Tell me whether you’re going to be in town next week" clearly means 'a reply is desired one way or the other.'