Here’s a finer point of grammar that I probably learned years ago. On page 763 of Infinite Jest, Mario is talking to his mother:
Mario: “How can you tell if somebody’s sad?”
Avril: “You mean whether someone’s sad.”
Not being able to recall the distinction between “if” and “whether”, I asked the question of the Infinite Summer forum and got this response from user isabella:
From Bryan A. Garner’s A Dictionary of Modern American Usage (which DFW discussed at length in “Tense Present: Democracy, English, and the Wars Over Usage”):
It’s a good 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.
Copyeditors (I am one) generally try to maintain the distinction.