Study this example situation:
Sarah wants to phone Paul, but she can't do this because she doesn't know his number. She says:
If I knew his number, I would phone him.
Sarah says: If I knew his number .... This tells us that she doesn't know his number. She is imagining the situation. The real situation is that she doesn't know his number.

When we imagine a situation like this, we use
if + past (
if I
knew /
if you
were /
if we
didn't etc.). But the meaning is present,
not past:
- There are many things I'd like to do if I had more time. (but I don't have time)
- If I didn't want to go to the party, I wouldn't go. (but I want to go)
- We wouldn't have any money if we didn't work. (but we work)
- If you were in my position, what would you do?
- It's a pity he can't drive. It would be useful if he could.
We use the past in the same way after wish (I wish I knew / I wish you were etc.). We use wish to say that we regret something, that something is not as we would like it to be:
- I wish I knew Paul's phone number. (= I don 't know it and I regret this)
- Do you ever wish you could fly? (you can't fly)
- It rains a lot here. I wish it didn't rain so much.
- It's very crowded here. I wish there weren't so many people. (there are a lot of people)
- I wish I didn't have to work tomorrow, but unfortunately I do.

If I were / if I was
After
if and
wish, you can use
were instead of
was (
if I were /
I wish it were etc.).
If I was /
I wish it was are also possible. So you can say:
- If I were you, I wouldn't buy that coat. or If I was you, ...
- I'd go for a walk if it weren't so cold. or ... if it wasn't so cold.
- I wish she were here. or I wish she was here.
We do not normally use
would in the
if-part of the sentence or after
wish:
- If I were rich, I would travel a lot. (not If I would be rich)
- Who would you ask if you needed help? (not if you would need)
- I wish I had something to read. (not I wish I would have)
Sometimes wish ... would is possible: I wish you would listen. See Unit 41 .
Could sometimes means 'would be able to' and sometimes 'was/were able to':
- She could get a better job if she could speak English.
(she could get = she would be able to get)
(if she could speak = if she was/were able to speak) - I wish I could help you. (I wish I could = I wish I was able)