It's clear to me that in some situations, "if" works but "whether" does not: 1a) If it rains, I shall take my umbrella. 1b) Call me if rain is predicted.

Also some where only "whether or not" will work: 2a) Whether or not it rains, I still have to go to work.

and some where only "whether" works: 2b) Whether you like this example is of no concern to me.

According to Grammar Girl, there are sitiations where the "or not" is superfluous, as it's not needed to clarify the meaning. 3a) Let me know whether you're going. 3b) Let me know whether or not you're going.

There are also situations where any of the three constructions would work, but the meaning is different:

4a) Let me know if rain is predicted. 4b) Let me know whether rain is predicted. 4c) Let me know whether rain is predicted or not. (to me, 4c above seems ambiguous as to what the speaker wants to know—the prediction or something else altogether— so it needs more context to clarify that)

Can someone succinctly explain which rules of grammar or syntax are operative in these examples, and whether there are other situations where other rules might apply for "if" VS "whether" VS "whether or not"?

Also, are there recognized differences in formal and casual usage?

  • I've fiddled with your title! Hope that's ok. Feel free to roll back. Or if you just want my name off your post then you could do an edit and fiddle about with a full stop or something! Jan 13 '15 at 14:44
  • This question just makes me realize that I just don't say whether at all. Speaking normally, I would replace all the whethers in OP's examples with ifs (and a little editing).
    – Gerger
    Jan 13 '15 at 15:57


Whether or not and if can both be used in conditionals:

  • Whether or not it rains, I'm going to the park.
  • If it rains I'm going to the park.

Notice though that the meanings are very different. In the first sentence I am definitely going to the park - whatever happens. However, in the second sentence, I may not be going to the park if it doesn't rain.

Whether on its own cannot be used in conditionals:

  • *Whether it rains, I'm going to the park. (ungrammatical)

If xyz or not is not often used in conditionals, it can sound awkward, if not ungrammatical, and is best avoided if you you're a learner.

  • #I'm going to the park if it rains or not. (awkward)

In conditional sentences, the word if is a preposition. It isn't a subordinator.


If XYZ, if XYZ or not, whether XYZ, whether XYZ or not, and whether or not XYZ are all used in subordinate interrogative clauses:

  • I don't know if she's working
  • I don't know if she's working or not.
  • I don't know whether she's working.
  • I don't know whether she's working or not.
  • I don't know whether or not she's working.

Notice that if or not XYZ is not grammatical:

  • *I don't know if or not she's working. (ungrammatical)

The not versions in the grammatical sentences above don't seem to make much difference to the meaning. However, they make the negative versions of the embedded propositions more salient.

If the interrogative clause comes at the beginning of the sentence, in other words if it is the subject in the sentence, then we have to use whether and not if:

  • Whether she's able to do this is unclear.
  • If she's able to do this is unclear. (ungrammatical).

We also strongly prefer whether to if when the interrogative clause is the complement of a preposition, such as about:

  • I'm unsure about whether she's there.
  • I'm unsure about if she's there. (may be deemed ungrammatical).


Commas can be useful for differentiating condition clauses from interrogative ones:

  • Let me know whether you're coming or not. (interrogative)
  • Let me know, whether you're coming or not. (conditional)

The first question wants the listener to say that they are coming or aren't coming. The second sentence asks the listener to tell them something (we don't know what this is, perhaps it's who won the FA cup final). If the listener is coming we need an answer and if the listener isn't coming we still need an answer (about who won the FA cup).

Hope this is helpful!

  • Hmm… can you give some reasoning for why if (and presumably when, whether, etc.) is a preposition rather than a subordinator in conditional clauses? I can't think of any (and Googling this is useless, just gives tons of pages talking about prepositions in general where the word if happens to be used in a sentence here and there). Jan 13 '15 at 15:06
  • @JanusBahsJacquet Well, this is from H&P 2002, obviously, where they've shoved the traditional class of subordinating conjunctions into the preposition category leaving only interrogative-if, whether, that*, for, infinitival-to, and one special use of how in a class called subordinators. The thinking behind conditional-if being Prep is that it heads the clause, it's clauses function freely as adjuncts (read adverbials), and it supposedly has a conditional 'meaning'. Interrogative-if on the other hand is deemed merely a marker of subordination ... Jan 13 '15 at 15:57
  • @araucaria: quite useful. The part about the comma solves the ambiguity of my last example. I've upvoted your answer, but how do I accept it— This was my first Question! Jan 13 '15 at 22:48
  • @BrianHitchcock Well, if you're sure! There's a grey silhouette of a tick on the left under where you up or down-vote the answer. If you click on it it will go green. That's never final btw. You can change your mind and give the tick to someone else if a much better answer comes along. Nice first question! Jan 14 '15 at 0:49

Poorly-organized thoughts:

  1. I disagree with your first 2b. "Whether or not you like this example is of no concern to me." seems valid to me.
  2. I agree with Grammar Girl and Strunk & White: "make every word tell". "Or not" is typically useless.
  3. In 1b, you assert that "whether" could not substitute for "if," but in your second 2b, the sentence is nearly identical and you do use "whether": "Call me" vs. "Let me know." I agree with you that "if" and "whether" have different meanings in these sentences, which I will explain below.
  4. I agree with you that the sentence construction of 2c creates ambiguity.

The word "if" expresses a conditional situation. "Whether" only sometimes expresses conditions, however, because it is also used to express uncertainty: "I'm not sure whether I will go to the Britney Spears concert."

So, if we make an apples-to-apples comparison, we will limit the our use of "whether" to only conditional expressions.

Google has a lovely definition of "whether" for this sense, "indicating that a statement applies whichever of the alternatives mentioned is the case." Because the outcome is irrelevant, appending "or not" to "whether", when used in this sense, is always logically permissible, even if it is stylistically discouraged.

Presto, we have our answer. If the outcome of the possible alternatives it irrelevant, then "whether" is your word. If the alternative that actually occurs will have an effect, then "if" is king.

Edit, but see the comment below

Is "I'm not sure if I will go to the concert." incorrect? – EFrog

  • Mostly makes sense to me, but still a couple of uncertainties. How is 2b) like 1b)? In 1b) "if" is in an adverbial clause, whereas in 2b) "whether" is part of a noun phrase which is the subject of the sentence. Are you saying that "if" would work in 2b)? If so, why? The other confusing ghing is that you say "whether" only sometimes expresses conditions, then you go on to say we will "limit our use of whether to only conditional expressions". This seems contradictory. Jan 13 '15 at 7:35
  • My answer was certainly not my best prose. On the second question, I was trying to say that "whether" has multiple definitions and that I was going to narrow the discussion to only the definition that was most similar to "if", which is the sense of conditional expressions. As in, "If this, then that." My computer background may be inhibiting my ability to express this in a non-nerdy way. Jan 13 '15 at 7:50
  • Ok, got it. And I fixed numbering in Q so no dupes! but i'm wondering: if we should "make every word tell", and thus "or not" is "typically useless", why would it be needed in my first (now only) 2b)? Jan 13 '15 at 8:03
  • It's not needed, but I think it is grammatically permissible. I prefer to think of grammar as a spotlight for the picture I paint rather than as a cage trapping my words. If your sentence powerful expresses your thoughts, then grammar be damned! Jan 13 '15 at 8:19
  • 2
    Is "I'm not sure if I will go to the concert." incorrect?
    – EFrog
    Jan 13 '15 at 9:42

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