Whether can be a problem word for many writers and editors. Should it be followed by or not? Should it be replaced with if? Whether you need them or not, here are some guidelines to help you gauge your whether.
Adding ‘or Not,’ or Not
Adding or not after whether is usually unnecessary; whether implies a choice, and therefore also implies the or not. So in formal writing, it’s usually best avoided.
In informal and conversational writing, of course, you have more elbow room. Whether or not is still superfluous, but it’s no great grammatical sin. In fact, it can be used to good effect to emphasize the choice or to imply that the not is the more likely option.
Regardless of the register of the writing, though, there is a time when the or not is necessary: when whether or not means “regardless of whether,” and of course you can use that phrase as well.
The fair will go on regardless of whether it rains.
The fair will go on whether or not it rains.
Keep your eye out for sentences that use both regardless and or not, which is truly pointless and redundant — and an easy problem to miss. Though it’s a cinch to see the problem with a sentence like
*Regardless of whether or not Elliot pitches in, we’re buying a new coffeemaker for the office.
in isolation, if you’re reading quickly, it can be annoyingly easy to miss.
The other common dilemma for whether is its relationship to the word if, and when you should use one and the other. Again, informal registers give you more leeway, but in formal written English, you should retain the distinction.
Whether implies a choice:
I don’t know whether to buy the shoes or the nose ring.
The study didn’t reveal whether the drugs were effective.
This spell won’t work if he doesn’t chant.
The only way this car will move is if we push it.
There are plenty of example sentences in which both if and whether fit the bill grammatically, but those sentences have subtly different meanings. For example, Let me know if my mother calls implies that the speaker wants to be notified only if her mother calls. (Note that the statement is equivalent to If my mother calls, then let me know.)
Let me know whether my mother calls implies that the speaker wants to be told at some future point either that her mother did call or that she didn’t.
And perhaps it’s these subtle differences that have led to the overuse of or not, especially in spoken English. Let me know whether or not my mother calls makes the speaker’s meaning perfectly clear. Either of the other constructions might lead to a request for clarification, especially if the receiver of the statement knows that the speaker is worried about her mother.
In short: In formal writing, when both if and whether seem to fit, whether is usually the one you want, and or not more often than not can be omitted.