If the lava comes down as far as this, we will evacuate these houses
Someone wrote to me as follows.
(a) If the lava comes down as far as this, we will evacuate these houses.
(b) If the lava will come down as far as this, we will evacuate these houses.
Syntactically, both (a) and (b) are correct. But semantically, (a) is not understandable because if the lava ( from the volcano ) comes down as far as THIS, it will be too late to evacuate THESE houses. So if the lava WILL ( = is likely to ) come down as far as this, we must evacuate these houses immediately.
I think interpreting (a) as the person does is unnatural. I would like to know native English speakers' opinions.
A similar(but different) question was asked here(https://ell.stackexchange.com/questions/60972/if-the-lava-will-come-down-as-far-as-this-we-will-evacuate-these-houses).
EDIT(21 July 2015) Perhaps explaining the backgound of my question might help.
We were discussing which sentence is correct, (a) or (b). I think (a) is correct and (b) is incorrect, because there is the following grammar rule. http://www.englishcafe.jp/englishcollege/etense2/e1-2-4.html "In the time and the conditional clauses, both of the present tense and the past tense are used, but "will" and "shall" is usually not used even if it means the simple future. It is inevitable that the present tense is used instead."
However some people say that there are exceptions that we use "will" in if-clauses.
Practical English Usage §260 If … will
We normally use a present tense with if (and most other conjunctions) to refer to the future. I’ll phone you if I have time. (NOT … if I will have time.) But in certain situations we use if … will.
1 results We use will with if to talk about what will happen because of possible future actions – to mean ‘if this will be the later result’. Compare: – I’ll give you ￡100 if I win the lottery. (Winning the lottery is a condition – it must happen first.) I’ll give you ￡100 if it’ll help you to go on holiday. (The holiday is a result – it follows the gift of money.) – We’ll go home now if you get the car. (condition) We’ll go home now if it will make you feel better. (result)
2 ‘If it is true now that …’ We use will with if when we are saying ‘if it is true now that …’ or ‘if we know now that …’. If Ann won’t be here on Thursday, we’d better cancel the meeting. If prices will really come down in a few months, I’m not going to buy one now.
3 indirect questions: I don’t know if … We can use will after if in indirect questions. I don’t know if I’ll be ready in time. (NOT … if I’m ready in time.)
4 polite requests We can use if + will in polite requests. In this case, will is not a future auxiliary; it means ‘are willing to’. If you will come this way, I’ll show you your room. If your mother will fill in this form, I’ll prepare her ticket. Would can be used to make a request even more polite. If you would come this way …
5 insistence Stressed will can be used after if to suggest insistence. If you WILL eat so much, it’s not surprising you feel ill.
EDIT 2(21 July 2015) Some people say it all depends on context. They say (a) may be incorrect and (b) may be correct depending on context. But I cannot imagine such a case.
Solution 1:
These are conditional statement, we both know that second statement is wrong. Here in rules for conditional statement where 'If + simple future tense' doesn't exist but 'If + simple present ; simple past ; perfect past' is used only.
If you use 'If + simple present' + main clause (future tense) means if this thing happens that thing will happen. 1. If you don't hurry you will miss the train. And there is also another condition rule in that 'if + simple present' + main clause (simple tense) means if this thing happens that thing happens. 1. If you heat ice it melts.
Solution 2:
The question is about the use of "IF".
In the original question or,later, in the edited portion this use of "IF" comes up for consideration.
In clauses of time and conditions, simple present is used (the clause may start with if/till or the likes). Rules are commonsense tasted by time. We use simple present to mean near future. So the "if" clause with present tense makes the resultant principal clause a bit more distant in the future. No harm. That is as it should be.
So option (1) is correct, the other not at all. It seems to me, with both the clauses in the future, we would be really in a fix as to looking at lava or taking to our heels.
A few more words about the usage of ###"IF".
'IF' is a structural word introducing condition. It introduces three type of condition.
1) OPEN CONDITION as shown in question. • If you find the pen, I'll give it to you.
2) UNFULFILLED CONDITION : • If you had seen him, you could have saved him. (Notice the sense of distance/ time factor between the clauses)
3) IMPROBABLE CONDITION : • If I had the wings of a bird (or, if I were a bird), I would fly.
It may be noted that in sl no (2)&(3) principal clause takes--could/should/might/would--and in (2)perfect form of verb and in(3) only verb.
These "could, should et al " are not necessarily past form but such words that are there by their own rights to convey the sense of fulfilment of condition but maintaining distance as well.