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“Whether or not” vs. “whether”

I am not sure about the usage of whether. My confusion over it is whether or not is optional. Suppose I have the following sentence:

The results of the pathological test will definitely show whether the frail patient has an infection or not.

Is or not compulsory to make this sentence more appropriate, or is it optional?

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marked as duplicate by RegDwigнt Dec 21 '12 at 11:32

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

As @jlovegren says, [or not] is superfluous, and if that's all the second condition consists of, you can discard it if you want. But in practice, we usually use if rather than whether in such contexts anyway. Note that even with if, you can still usually stick [or not] on the end. But that's not at all common, obviously. – FumbleFingers Dec 21 '12 at 6:00
up vote 4 down vote accepted

Whether is used to form indirect polar (yes/no) questions. A polar question refers to two conditions, but they are logically related and so one condition can be inferred from the other.

From a functional standpoint, then, [or not] is superfluous. Not surprisingly, most indirect questions formed with whether can have [or not] omitted.

A separate issue to be raised, if you choose to keep [or not], is where to place it. You can choose either:

...whether [or not] the frail patient has an infection.
...whether the frail patient has an infection [or not].

The best guideline is that when the proposition under question is "heavy" (many words), use whether or not..., and when it is "light", use whether...or not.

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and "if the frail patient has an infection [or not]", but I would certainly balk at "if or not the frail patient has an infection" – FumbleFingers Dec 21 '12 at 6:04
@FumbleFingers: Is there any reason as to why you would say if rather than whether or it is just so? Is it about formality? – Gigili Dec 21 '12 at 9:43
@Gigili: Well, I doubt native speakers would normally stop and think "Shall I use if or whether here?". But if is shorter, and almost certainly it's far more common, so I imagine it would just tend to get used more often in contexts where both are equivalent. I don't think there's any real sense in which you could say whether is more "formal". – FumbleFingers Dec 21 '12 at 17:26
Whether is the Wh-word for Yes/No questions; it converts them to Wh-questions so that they can be embedded safely and marked as questions, even though they don't have subject-verb inversion or Do-support. E.g: He asked me "Did you see it"? ==> He asked me whether I saw it. "Or not" is just a flourish, like a tag question. – John Lawler Dec 21 '12 at 17:47

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