Could someone please help me with these sentences? I need to know

  1. Which one doesn’t sound natural?
  2. Which one is formal and which one is not?

A - I don’t know whether this word fits in the sentence.
B - I don’t know if this word fits in the sentence.

C - I don’t know whether or not this word fits in the sentence.
D - I don’t know if or not this word fits in the sentence.

E - I don’t know whether this word fits in the sentence or not.
F - I don’t know if this word fits in the sentence or not.

For me only D doesn't work and sounds not idiomatic. Meanwhile for me all of these sentences can be used in both written and spoken languages. Do you confirm me?


You are exactly right; (D) is not usually acceptable, but all the others are.

There are however other circumstances in which whether and if are used somewhat differently, and different rules apply.

You raise, in effect, three distinct questions:

  1. When may if be substituted for whether?
    This is an easy one: if may always be used in any expression which employs whether. (But as we will see, some syntactical adjustments may be required.)

  2. When is or not permitted or required in expressions with whether and if in that sense, and how is it deployed?
    Whether and if are used to introduce clauses expressing a choice between two or more alternatives in two contexts:

    • In complement clauses

      I need to know whether this word fits in this sentence or does not fit in this sentence or fits only sometimes.
      I need to know if this word fits in this sentence or does not fit in this sentence or fits only sometimes.

      I need to know whether this word fits in this sentence or does not fit in this sentence.
      I need to know if this word fits in this sentence or does not fit in this sentence.

      In situations like the second pair, where there are only two alternatives and one is simply the negation of the other, you may replace the second alternative with a bare not:

      I need to know whether this word fits in this sentence or not.
      I need to know if this word fits in this sentence or not.

      In fact, you can omit the or clause altogether; the absence of an explicit or implies that the negative is intended:

      I need to know whether this word fits in this sentence.
      I need to know if this word fits in this sentence.

      The phrase or not may be moved immediately after whether, but this is not generally used with if:

      okI need to know whether or not this word fits in this sentence.
      ??I need to know if or not this word fits in this sentence.

    • in condition clauses
      When whether and if are used to head the ‘protasis’ (IF or condition clause) in a conditional construction, the rules are different.

      With whether, there must be an explicit or clause or phrase:

      okWhether the word fits or does not fit, spell it correctly!
      okWhether the word fits or not, spell it correctly!
      okWhether or not the word fits, spell it correctly! ... BUT
      Whether the word fits, spell it correctly!

      And if cannot be simply substituted for whether in a condition clause, because in that context whether implies that the consequence is true or actualized if either condition is in force. You have to employ an if clause that expresses that meaning. With just two alternatives you may employ either or if or both if...and if:

      If the word fits or if it does not, spell it correctly!
      Both if the word fits and if it does not, spell it correctly!

      These are grammatically and logically sound, but clunky; and there really is no graceful way to express three or more alternatives using if, since the introductory both, which alerts the reader to the structure which will follow, is not applicable. Stick with whether.

  3. Are these uses of if restricted to informal use?

    It's not really a matter of formality v. informality, but of monologue v. dialogue. In conversation, where any misunderstanding is easily corrected, if is entirely acceptable.

    But in writing, or in spoken contexts such as lectures and broadcasts which do not involve participation by the hearer, you want to make what you are saying as easy for the addressee to ‘process’ as possible. The “rule” here is to use the most explicit term possible. Since if has a very broad range of syntactic and semantic meanings, while whether has a relatively narrow range, your choice should always be to use whether rather than if in circumstances where either is acceptable.

    And there is really no reason to avoid following this practice in conversation as well. It will not mark your speech as pedantic or highfalutin—everybody understands and uses whether.

FumbleFingers points out that this use does appear from time to time, but acknowledges that it sounds “strange”. That, to my mind, means ‘Don’t use it’.

marks an utterance as ungrammatical.

  • I may be wrong here (and of course it all depends on exactly what we mean by "ungrammatical"), but I'm not entirely convinced ungrammatical is the right word there. I completely agree "Whether the shoe fits, wear it!" doesn't sound at all "good" to my ear, but it seems to me non-idiomatic describes it better. Apr 27 '14 at 14:04
  • It's a bit like whichever/whatever as opposed to which/what, in that you can say "Whichever you want, just tell me and I'll get it for you", but somehow it doesn't work if we just try to use which there. I can only think this is a matter of idiomatic familiarity, not grammar as such. Apr 27 '14 at 14:11
  • @FumbleFingers On the one hand, everything may be regarded as grammar; on the other, everything may be regarded as idiom. My canon of 'ungrammaticality' is whether I can formulate an explicit generally-observed grammatical rule which excludes it: that whether in conditional clauses requires an explicit or- complement, just as a transitive verb requires a direct object. Apr 27 '14 at 14:12
  • 2
    @FumbleFingers They're only 'always interchangeable' in one direction; whether can only rarely be substituted for if. For instance, you can't say Whether you pass the salt shaker, make sure the holes are facing up. The real odd-man-out is that if or not: certainly we could say it, but the fact is we don't. It's been on the ballot for a long time, and the voters just don't like it. Apr 27 '14 at 15:44
  • 1
    Huddleston and Pullum put it this way: there are two words with the shape if. One of them is a subordinator interchangeable with whether ("See if/whether there are any vacancies"). The other has a conditional meaning and is not interchangeable ("I'll help you if/*whether I can").
    – user230
    Apr 27 '14 at 22:13

There's no grammatical rule to say any of OP's variants are "incorrect". For example...

There haven't been enough studies to determine if or not there truly are negative effects...

It's just that idiomatically we don't use that form so often, so it may appear "strange". But here are a few hundred instances of decide if or not if you want to practice getting more used to that version.

In light of StoneyB's answer (and comments thereto), I think it's worth pointing out that James McCawley, in what's probably the definitive reference book The Syntactic Phenomena of English devotes several pages to this particular usage. At the end of which he writes...

I suggest a deep structure like [what he's just set out] without enthusiasm, but also without any idea of how else the different kinds of alternative questions could be given an analysis that is at all unified.

Effectively, what McCawley is concluding there is that undeniably native speakers do have commonly-agreed preferences about contexts where if/whether are not interchangeable, but no-one (including him) can come up with a coherent "grammatical rule" to describe what exactly governs our thinking.

Mostly I think what this amounts to is if is such a short, common word that we've gotten used to using it in a wider variety of "conditional" contexts. But whether remains far more tightly bound to "binary choice, yes or no" contexts, so it's best to avoid it unless the single alternative (or not) is explicitly specified.

  • 1
    True; but according to Google Ngrams we're currently running about 9,750:1 in favor of whether or not, if or not having spiked at a little over 1 in 200 in 1823! Apr 27 '14 at 13:41
  • @StoneyB: True, but regardless of whether we might consider this sentence itself to be an exceptionally unusual usage, only a brave (or foolhardy) pedant would presume to cite a "grammatical rule" debarring it! :) Apr 27 '14 at 13:58
  • +1 very nice. Part of the answer, of course, is that 'alternativity' is part of the semantics of whether - it is, after all, etymologically composed with other. By the way, does your Dickensian variation on McCawley's name suggest that you expect something will turn up? :) Apr 27 '14 at 15:50
  • @StoneyB: Oh corks! Will edit. I guess the ole brain was still woozy from trying to even follow the "grammar" he was tentatively advancing. But yeah - I do note the whether / other / either connection. Apr 27 '14 at 22:46

tl;dir version: Whether usually implies that it must be one of the options presented, if usually implies that it may be none of them.


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