Page 88 - English Grammar in Use

Unit
38 if I do … and if I did …

A Compare these examples:
(1) LISa: Shall we take the bus or the train?
JESS: If we take the bus, it will be cheaper.
For Jess, it is possible that they will take the bus,
so she says:
If we take the bus, it will be …
If we take the bus,
LISA JESS it will be cheaper.

(2) Lisa and Jess decide to take the train. If we took the bus, it would be cheaper.
Later, Jess talks to Joe.
JOE: How are you going to travel?
JESS: We’re going to take the train. If we took the bus,
it would be cheaper, but the train is quicker.
Now Jess knows they are not going to take the bus,
so she says:
If we took the bus, it would be … JOE JESS

B When we talk about something that will not happen,
or we don’t expect that it will happen, we use
if + past (if we went / if there was etc.).
But the meaning is not past:
What would you do if you won a lot of money?
(I don’t really expect this to happen)
If there was an election tomorrow, who would
you vote for?
(there will not be an election tomorrow) If I won a lot of money …
I’d be surprised if they didn’t come to the party.
(I expect them to come)
Compare if I find and if I found:

I think I left my watch at your house. If you find it, can you call me?
but
If you found a wallet in the street, what would you do with it?

C We do not normally use would in the if-part of the sentence:
I’d be very scared if somebody pointed a gun at me. (not if somebody would point)
If we went by bus, it would be cheaper. (not If we would go)

In the other part of the sentence (not the if-part) we use would (’d) / wouldn’t:
I’d be (= I would be) scared if somebody pointed a gun at me.
I’m not going to bed yet. I’m not tired. If I went to bed now, I wouldn’t sleep.
What would you do if you were bitten by a snake?
Could and might are also possible:
If I won a lot of money, I might buy a house.
(= it is possible that I would buy a house)
If it stopped raining, we could go out.
(= we would be able to go out)

will ➜ Units 21–22 if and when ➜ Unit 25D would ➜ Unit 36 if I knew ➜ Unit 39
76 if … was/were ➜ Unit 39C if I had known ➜ Unit 40