Study this example situation:
Tom wants to call Sue, but he can’t because he doesn’t know her telephone number.
If I knew her number, I would call her.
Tom says “If I knew her number…" This tells us that he doesn’t know her number.
He is imagining the situation. The real situation is that he doesn’t know her number.
When you imagine a situation like this, you use a past tense form (“I did / I had /1 knew,” etc.) after if. But the meaning is present, not past:
• Tom would travel if he had more money. (but he doesn’t have much money)
• If I didn’t want to go, I wouldn’t. (but I want to go)
• We wouldn’t have any money if we didn’t work. (but we work)
We also use the past for a present situation after wish. We use wish to say that we regret something, that something is not as we would like it to be:
• I wish I knew Sue’s telephone number. (I don’t know it.)
•Do you ever wish you could fly? (You can’t fly.)
•I wish it didn’t rain so much in this city. (It rains a lot.)
It’s crowded here. I wish there weren’t so many people. (There are a lot of people.)
•I wish I didn’t have to work. (I have to work.)
In if sentences and after wish we use were instead of was:
• If I were you, I wouldn’t buy that coat. (hut I am not you)
• I’d go out if it weren’t raining. (but it is raining)
• I wish my room were larger. (but it isn’t very large)
Do not use would in the if part of the sentence or after wish:
• If I were rich, I would buy a castle. (not if I would be rich)
• I wish I were taller. (not I wish I would he taller.)
But sometimes I wish. . . would.. . is possible.