If you ___________ come by 12 o'clock tomorrow, let me know right now.

A) won't
B) don't

In an if sentence we should use present tense, but it feels like it doesn't make sense if I use "don't" and "won't" makes more sense. But would that be correct usage?

Edit: I changed the "from now" that is mentioned in some of the answers.

  • 1
    "Let me know from now"? What does that mean? For the first clause, if you don't come is normal; normal doesn't have to make sense. However, if you won't come is not normal and doesn't mean the same; it means "if you're not willing to come by 12", because that's what will means in in if clause Feb 9 '17 at 16:38
  • However, if the verb is changed to "If you won't arrive by 12", then that's a perfectly normal negation of [what is normally called] the future tense. The use of come certainly isn't idiomatic for that sense, though. Feb 9 '17 at 16:57

These two versions sound more natural:

"If you won't come by 12 o'clock tomorrow, let me know now." That means you want to plan and prefer if you know in the present that he will or won't come at that time.

"If you don't come tomorrow, I will end up in trouble, so I'd rather know now." That means if tomorrow at noon passes without his arrival, you will suffer and would prefer to plan otherwise by knowing the bad news now.


I'm not sure why you got the idea that you cant' use the future tense in an "if" sentence, since most conditionals deal with potential future events. So it's fine to say:

If you will/won't come to my party ...

If you will/won't buy groceries this evening ...

If you will/watch that movie with me ...

And so on. It is not correct grammar to use "don't" in the future tense, although you may express some kind of present action that affects something in the future:

If you don't want to come to my party tomorrow ...

If you don't have time to buy groceries this evening ...

If you don't feel like watching that movie with me ...

Lastly, "let me know from now" is not natural English. Instead we would just say "let me know". Examples:

If you won't come to my party, please let me know?

If you won't buy groceries this evening, please let me know (so I can buy them this afternoon)

If you won't want to watch that movie with me, let me know (so I can ask someone else).

  • 1
    The reason is that we can only use will with certain meanings in conditional apodoses. It's the first thing that language learners learn about English conditionals. Consider "I'm going to buy a Ferrari if I will win the lottery" or "If you will have an accident, call this number". Feb 9 '17 at 21:01
  • Notice that in your conditionals, will unusualy has the meaning of want to or decide to a bit like the will in Do what you will. Feb 9 '17 at 21:11

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