Sentence 1:We discussed if we should close the shop.
Sentence 2:We discussed whether we should close the shop.
Sentence 3: I doubt if they'll make it.
Sentence 4: I doubt whether they'll make it.
Which sentence sound natural to you?
Is there a rule that we should use "whether" rather than "if" after "discuss" in an object clause?
Thank you very much!
Best Answer
It seems that "doubt whether" was far more common for a long time, but the usages have largely converged, and both appear to have currency.
Personally, I prefer "whether" in both of these cases, but I would not see a big distinction between them. Neither usage would mark a speaker as being non-native or particularly regional to me, nor seem out of place. I would find "if" in these sorts of sentences to be somewhat more casual, however.
I am not aware of any rule governing which one to use... if you're in doubt, I would go with "whether" when you are discussing a true-or-false/yes-or-no condition in an object clause like this.
You didn't ask, but note that "I doubt they'll make it" is also acceptable. That's particular to the verb doubt though.