In an eerie coincidence, two acquaintances almost simultaneously sent me e-mail messages that concerned the proper use of whether. One suggested that my use of whether should have been if. The other wondered if the phrase whether or not contains two unnecessary words.
Let’s consider these issues in turn. First, whether vs. if.
Garner’s Modern American Usage, one of the best resources on grammatical matters, advises:
“It’s good editorial practice to distinguish between these words. Use if for a conditional idea, whether for an alternative or possibility. Thus, Let me know if you’ll be coming means that I want to hear from you only if you’re coming. But Let me know whether you’ll be coming means that I want to hear from you about your plans one way or the other.”
Now for the second question: Is the or not in whether or not superfluous?
Garner and other grammarians say that it usually is. For example, in the sentence “A new test can predict whether or not a relationship will last,” the words or not can be deleted because the word whether implies or not.
But in some cases, the or not is necessary. Consider this sentence: “The show will go on whether or not the star is ill.” Here, the or not is clearly required. Alternatively, the sentence could be rephrased as “The show will go on regardless of whether the star is ill.”