Whether VS If

The examples here are showing "whether" and "if" as part of noun clauses.
There are many more variations such as:

I don't know whether or not she is coming.
I don't know whether she is coming or not.
I don't know if she is coming.
I don't know if she is coming or not.

English is an expressive language, and the difference comes down to formality and emphasis.

The word "if" is much more common and therefore lends itself to the spoken language. The word "whether" is more formal and less used, and therefore is used in more formal spoken and written situations.

To add "or not" adds emphasis to the uncertainty of the speaker.

Of course, "if" is also used in those conditional clauses too. e.g.
"If you don't have an umbrella, you'll get wet". And in a written piece that has a mixture of conditional clauses and noun clauses, a writer may choose to prevent confusion by using "whether" to begin the noun clauses instead of "if".

If you knew if Bill was coming, why didn't you see if Sally wanted to come too?
If you knew whether Bill was coming, why didn't you see whether Sally wanted to come too?

I would personally choose one and stick with it for personal use. If you want to sound more formal, then "whether" will work for you. If you want to sound more casual and laid-back, use "if".

So in a nutshell, sentence 1 is formal and sentence 2 is more casual. The same goes for A and B. Hope that helps.

Jon Petruch
Linguist and English Teacher

The words if and whether are sometimes interchangeable, but not always.

Use if or whether:

When reporting yes/no questions:

I am unsure whether I will be going to work tomorrow
I am unsure if I will be going to work tomorrow.
(In this example, the yes/no question is "Will I be going to work tomorrow?")

John wondered whether he had locked the door.
John wondered if he had locked the door.
(In this example, the yes/no question is "Did John lock the door?"

In whether/if...or...constructions:

I would like to know whether it is a true story or fabricated.
I would like to know if it is a true story or fabricated.

Use whether:

To present two alternatives (neither of which is a condition):

Tell me whether John needs a seat.
(In this example, the two alternatives are John needs a seat and John does not need a seat. I am to be informed in either case.)

"Tell me if John needs a seat" is not grammatically wrong, but it does not mean the same as the first example. In this example, I am only to be informed if John needs a seat, which is a condition.

Let me know whether my mother is going to London. The two alternatives are going and not going. I need to know the answer regardless of which is chosen.

When whether starts a clause that is the sentence subject or complement:

Whether you sink or swim is not my concern.
(Whether you sink or swim is the subject of this sentence.)

I don't care whether you sink or swim.
(Whether you sink or swim is the complement of the verb to care.)

In formal writing.

(When if and whether are interchangeable, choose whether in formal writing.)

I doubt whether the team will succeed.

Please establish a committee to determine whether the proposed funding lines are appropriate.

Thank you so much your the elaborate explanation.
It's been quite tough to distinguish them, and honestly though I'm still unable to completely comprehend the difference, I feel I like I can understand the problem in any minute just by reading your illustrations. I got it printed and I am reading it over and over again. Thank you.

Thank you Contrex.
I've always appreicated your help and I still do.
Thank you so much.