'If' Versus 'Whether'

Today's topic is "whether" — not rain or snow, but whether w-h-e-t-h-e-r, as in whether you like it or not, it's the topic.

First, let's figure out when to use "whether" and when to use "if."

'If' Versus 'Whether'

Although in informal writing and speech people often use "if" and "whether"  interchangeably, in formal writing, such as in technical writing at work, it's a good idea to make a distinction between them because the meaning can sometimes be different depending on which word you use. The formal rule is to use "if" when you have a conditional sentence and "whether" when you are showing that two alternatives are possible. Some examples will make this more clear.

Here's an example where the two words could be interchangeable:

Squiggly didn't know whether Aardvark would arrive Friday.

Squiggly didn't know if Aardvark would arrive Friday.

In either sentence, the meaning is that Aardvark may or may not arrive Friday.

Now, here are some examples where the words are not interchangeable:

Squiggly didn't know whether Aardvark would arrive Friday or Saturday.

Because I used "whether," you know that there are two possibilities: Aardvark will arrive Friday, or Aardvark will arrive Saturday.

Now see how the sentence has a different meaning when I use "if" instead of "whether":

Squiggly didn't know if Aardvark would arrive Friday or Saturday. 

Now in addition to arriving on Friday or Saturday, it's possible that Aardvark may not arrive at all. 

These last two sentences show why it is better to use "whether" when you have two possibilities, and that is why I recommend using "whether" instead of "if" when you have two possibilities, even when the meaning wouldn't change if you use "if." It's safer and more consistent.

Here's a final pair of examples:

Call Squiggly if you are going to arrive Friday. 

Call Squiggly whether or not you are going to arrive Friday. 

The first sentence is conditional. "Call Squiggly if you are...

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