Could you tell me if it's incorrect to say:

I don't know whether I watch ABC or NBC.

I don't know whether to watch ABC or NBC.

I know they both are weird and if I add a modal verb such as "should" it'd solve the problem, but I'd like to know what exactly is sintatically unsuitable here? Is there any rule?


Both are grammatically correct but don't mean the same thing.

The most common usage is that in your second example. Compare with this similar example found in the Cambridge dictionary:

We use whether … or to introduce a clause giving two options or alternatives:

"I can’t decide whether to paint the wall green or blue."

"She didn’t know whether he was laughing or crying."

In your first example, the only potential problem does not lie with your use of "whether", but with the semantics of the clause "I watch ABC or NBC". It is grammatically correct, but it does not mean the same as your second sentence. Compare with the following example:

"I don't know whether he watches ABC or NBC" Meaning that you don't know what he usually watches.

The way you have phrased it is analogous. If you want to convey that meaning (you don't know what channel you usually watch). it would be correct.

On the other hand, you cannot use that to convey the same meaning as in "I don't know whether to watch...". Suitable alternatives for that would be using a modal verb, as you suggested, or using a future tense: "I don't know whether I will watch ABC or NBC"

  • (1) I believe that your answer is a little misleading, insofar as it opens with “Your second example is correct.” and doesn’t get around to adding that the first example is also grammatically correct until the seventh line.  I wouldn’t assume from the question that the OP intends the sentences to mean the same thing. (2) It seems plausible that a person might know what TV stations he watches, without knowing what their network affiliations are.  Also, in a multiple-person household, if one person controls the remote, the other person might not even know what channels she watches.
    – Scott
    Oct 5 '16 at 23:53
  • Thank you. You are right, and I have edited the answer accordingly. I hope it is clearer now.
    – Rubén
    Oct 6 '16 at 4:17

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