Hello,

Let's talk about the difference between "if" and "whether."

First of all, "whether" is not the same as "weather"! :-)
 
When we say "weather" we mean "the conditions around you, such as temperature,
wind, rain, snow, sun, etc.
 
For example, you could ask someone "how is the weather?"
 
So "whether" has a completely different meaning than "weather."

Whether

We use the word "whether" to show there is doubt about something, or that there are two different options.
 
For example, the sentence "Marry asked whether we needed her help" means that Marry was not sure if we needed her help or not, so she wanted to find out.


 
Some more examples:

• Did you ask whether Julie is coming back?
  (Meaning: Is Julie coming back or not?)
   
•  I don't know whether we should tell them.
  (Meaning: I am not sure. Should we tell them or shouldn't we?)
   
• Kelly doesn't know whether to thank you or kill you.
  (Meaning: Kelly may thank you, or she may kill you.)
   
• They asked us whether we took the money.
   
• I was not sure whether I should stay or leave.
   
• We do not know whether this theory is corrector not.

 
"Whether" is also used to show that something will happen no matter what.
 
Examples:

• I will sell the house whether you like it or not!
  (Meaning: you may like it, and you may not like it, but I am going to sell the house!)
   
• You will get the salary raise whether you accept the new position or not.
   
• Someone has to do something, whether it's us or them.
   
• He drives his toy car whether his parents allow it or not.

 
Until now we discussed "whether." Now let's explain what "if" means.

If

We use the word "if" to show a condition. 
Meaning, that something depends on something else.
 
Examples:

• If you help me, I will give you the money.
   
• If she wins the contest, she will get a new car.
   
• If you don't tell the truth, they will not forgive you.
   
• He will arrive on time if he rides fast enough.

 



The word "if" is also used to ask whether something is true.
 
Examples:

• Do you know if they are selling the house?
  (Meaning: Is it true or not that they are selling the house?)
   
• Did John tell you if he passed the exam?
   
• I wonder if I should tell her the truth.

 
Now, this sounds VERY similar to "whether." 
 
So what's the difference between "if" and "whether"?
 
When we want to know if something is TRUE or NOT TRUE, 
we can use both "if" and "whether."
 
For example:

• Charlie, do you know if they are selling the house?
  or
  Charlie, do you know whether they are selling the house?
• I wonder if I should tell her the truth.
  or
  I wonder whether I should tell her the truth.

Now, when there are several alternatives, "whether" should be used.
 
Examples:

• We are not sure whether it will be sunny or rainy.
   
• They haven't decided whether they should call the police or handle the situation themselves.

 
Finally, here is a good example to show you the exact difference between the use of "if" and "whether":
 
Both of these sentences have the same meaning:

I am not sure whether I should tell Monica.

or

I am not sure if I should tell Monica.

Option 1: I will tell Monica.
Option 2: I won't tell Monica.


However, these two sentences have two completely different meanings:
 
I am not sure whether I should tell Monica or Rachel.
 
Option 1: I will tell Monica.
Option 2: I will tell Rachel.
 

"I am not sure if I should tell Monica or Rachel."
 
Option 1: I will tell Monica or Rachel.
Option 2: I will not tell neither of them.