“Whether or not” vs. “whether”

Question

1. • This will depend on whether he's suitable for the job.
   • This will depend on whether he's suitable for the job or not.
   • This will depend on whether or not he's suitable for the job.
2. • It is still not defined whether we're following that approach.
   • It is still not defined whether we're following that approach or not.
   • It is still not defined whether or not we're following that approach.

"Or not" doesn't really seem to be needed to complement "whether". Why do people use it then? Is it redundancy and nothing more? Or is it for emphasis? Or are there cases when "or not" is required for the sentence to be grammatical?

Answer 1

The addition of the "or not" is neither logically nor grammatically required. I think it's often used conversationally for emphasis. I definitely wouldn't use it in writing myself.

Answer 2

It's worth pointing out that, etymologically speaking, the roots of whether are which/either of two. It's inherently a "binary choice" word, so whereas "I don't know whether it be fish or fowl" is fine, "I don't know whether it be fish or fowl or good red herring" isn't really grammatical. Which is not to say people never use that extended form - but it does sometimes attract criticism.

With "unary choice" forms such as "I don't know whether I like it", the alternative ("I don't like it") can invariably be shortened to "or not" - or simply discarded completely, since it's implicit anyway.

Possibly some will say if only one choice is presented, you should use "if" rather than "whether", but skimming through written instances of "Tell me whether" suggests that most people have always been quite relaxed on that point.

TL;DR: "or not" is never required if the alternative is a simple negation of the stated proposition, but an "or" clause is required in, say, "You must choose whether to write novels or poems" (presupposing that writing software is not an option currently on offer).

Answer 3

I'm surprised nobody mentioned this that I saw, so I'll post an answer.

The word whether should be used by itself in the situations you mentioned above. The “or not” is a mistaken crossover from the correct usage of “whether or not” mentioned below. It is often used that way, but when writing it's best to avoid that unnecessary bit.

The phrase whether or not is a condition, used in statements to show that something will or will not happen, regardless of certain other variables:

I'm going to go on strike whether or not anyone joins me!

This would be less correct, however, if used like this:

I don't care whether or not anyone joins me, I'm going on strike!