Grammar Girl here. I'm Minion Fogarty and you can think of me as your friendly guide to

the English language. We talk about writing, history, rules, and cool stuff. Today I'll

talk about when to use the words if and whether. They aren't always interchangeable.

And then I have a piece on why we say the odd phrase, the exception, proves the rule that

never made sense to me, but now I finally get it. But before we get started, multiple people

told me they have a different way of remembering that discrete spelled D-I-S-C-R-E-T-E means

something separate. And their trick is worth repeating. They notice that the two E's are separated

by the letter T. So if you'd rather think of the separating power of the letter T, then the beautiful

Greek island of Crete, whatever works for you, is a good tip. And I can definitely see how that

memory trick is simpler. And now onto the show. Although in informal writing and speech,

people often use if and whether interchangeably. Informal 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're showing that two alternatives are possible. Some examples will

help make this more clear. Here's an example where the two words could be interchangeable.

Squiggly didn't know whether Ardvark would arrive Friday. Squiggly didn't know if Ardvark would

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

Now here are some examples where the words are not interchangeable. Squiggly didn't know whether

Ardvark would arrive Friday or Saturday. Because I used weather, you know that there are two

possibilities. Ardvark will arrive Friday or Ardvark will arrive Saturday. Now see how the

sentence has a different meaning when I use if instead of weather. Squiggly didn't know if

Ardvark would arrive Friday or Saturday. Now in addition to arriving on Friday or Saturday,

...