Learn English – “If” and “Whether” – Is interrogative IF always replacable by WHETHER

questionssubordinate-clausessubordinatorssyntactic-analysis

I am asking here specifically about if and whether when they introduce embedded questions (or to be more technically accurate, subordinate interrogative clauses):

  • I don't know if Bob's here.
  • I don't know whether Bob's here.

In the sentence above we can freely replace if with whether. There are some situations in which the reverse does not apply. We cannot always replace whether with if. For example in standard English, we cannot normally use if after a preposition:

  • The question of whether he is actually eligible didn't arise.
  • *The question of if he is actually eligible didn't arise.

We cannot usually use interrogative-if directly followed by or not:

  • It's unclear whether or not he's a real elephant.
  • *It's unclear if or not he's a real elephant.

There are several more examples. However, what I want to know is:

  • Are there any examples where we can use interrogative-if but we can't use whether?

Edit note: There is an if that we find in conditionals that can't be replaced by whether. However, this is conditional, not interrogative, if.

Best Answer

  • There are a few verbs where I think "<verb> <interrogative clause>" in general is colloquial-but-acceptable, but where I think *"<verb> whether […]" in particular is ungrammatical; for example, consider "went to look if […]" vs. *"went to look whether […]", or "I can't think if I've […]" vs. *"I can't think whether I've […]".

    • In part this might be because whether is a bit more formal than if, so it doesn't work in these colloquialisms because the registers don't match; but I don't think that's a complete explanation, because I don't think the registers are so mismatched as to account for why the result sounds so ungrammatical (at least to me). (I'd welcome your thoughts on this.)

  • This is probably cheating, but I don't think if can be replaced with whether in an echo question:

    "I'm wondering if she, uh . . ." He trailed off.
    *"Whether she what?"

    (Note that this isn't completely trivial, since echo questions do allow some kinds of substitutions; for example, if the first speaker had said "Hannah" instead of "she", it would still be fine for the second speaker to substitute "she". And I think that echo questions can usually replace the zero complementizer with that and vice versa. But even so, I describe this as "probably cheating" because it's probably more a fact about echo questions than a fact about if and whether.)

  • You yourself pointed out in a comment above that something like "ask [if [whether …] …]" is clearly intelligible and grammatical, whereas something like "ask [whether [whether …] …]" is, um, not.

  • This is obviously cheating, but hey: colloquial/dialectal if'n can never be replaced with whether'n. ;-)

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