if they fight us/if they will fight us

[navi tasan]

1) If they fight us, we will fight them.
2) If they will fight us, we will fight them.
3) If they'll fight us, we will fight them.

What is the difference between the meanings of these sentences?

I think #1 is very natural. I don't think #2 and #3 are incorrect (I am not sure). I think they imply some kind of obstinacy on their part. 'Will' would mean 'want' here and won't be an auxiliary verb. The meaning would be: 'if they are intent on fighting'.

I included #3 because I find it less natural than #2. I am not sure that the contraction works well when the idea is to emphasize the fact that they are really hellbent on fighting!

 

[jutfrank]

I think they imply some kind of obstinacy on their part. 'Will' would mean 'want' here and won't be an auxiliary verb. The meaning would be: 'if they are intent on fighting'.

Yes, you're right about the meaning. However, 'will' is still an auxiliary verb even in this sense. It must be stressed, though, so the contraction (sentence 3) doesn't work. You can still contract in the result clause.

 

[Annabel Lee]

I included #3 because I find it less natural than #2. I am not sure that the contraction works well when the idea is to emphasize the fact that they are really hellbent on fighting!

There is another possible interpretation of #2 and #3, though, one where "will" doesn't have to do with volition; and on this other interpretation both #2 and #3 work equally well and are not equivalent to #1.

It's the type of conditional where the "if"-clause expresses background information that is given in the context: assuming P, then Q (where P is the proposition in the "if"-clause and Q is the proposition in the "then"-clause).

Renaat Declerck calls this type a "Closed-P conditional": "The supposition P is 'closed' if it is given in the context and the speaker assumes (at least ostensibly) that P is true" (Conditionals: A Comprehensive Emperical Analysis, 2001, p. 53).

A: I can assure you that they will fight us.​

B: If they will fight us, we will fight them. ​

​

A: I can assure you that they'll fight us.​

B: If they'll fight us, we'll fight them.​