A. Study this example situation:
Last month Gary was in hospital for an operation. Liz didn’t know this, so she didn’t go to visit him. They met a few days ago. Liz said:
If I had known you were in hospital, I would have gone to visit you.
Liz said: If I had known you were in hospital… . The real situation was that she didn’t know he was in hospital.
When you are talking about the past, you use if + had (‘d) … (if I had known/been/done etc.):
* I didn’t see you when you passed me in the street. If I’d seen you, of course I would have said hello. (but I didn’t see you)
* I decided to stay at home last night. I would have gone out if I hadn’t been so tired. (but I was tired)
* If he had been looking where he was going, he wouldn’t have walked into the wall. (but he wasn’t looking)
* The view was wonderful. If I’d had a camera, I would have taken some photographs.
(but I didn’t have a camera)
* I’m not hungry. If I was hungry, I would eat something. (now)
* I wasn’t hungry. If I had been hungry, I would have eaten something. (past)
B. Do not use would in the if-part of the sentence. We use would in the other part of the sentence:
* If I had seen you, I would have said hello. (not ‘If I would have seen you’)
Note that ‘d can be would or had:
* If I’d seen you, (I’d seen = I had seen)
I’d have said hello. (I’d have said = I would have said)
C. We use had (done) in the same way after wish. I wish something had happened = I am sorry that it didn’t happen:
* I wish I’d known that Gary was ill. I would have gone to see him. (but I didn’t know)
* I feel sick. I wish I hadn’t eaten so much cake. (I ate too much cake)
* Do you wish you had studied science instead of languages? (you didn’t study science)
* The weather was cold while we were away. I wish it had been warmer.
Do not use would have… after wish in these sentences:
* I wish it had been warmer. (not ‘I wish it would have been’)
D. Compare would (do) and would have (done):
* If I had gone to the party last night, I would be tired now. (I am not tired now – present)
If I had gone to the party last night, I would have met lots of people. (I didn’t meet lots of people – past)
Compare would have, could have and might have:
* If the weather hadn’t been so bad, we would have gone out.
* If the weather hadn’t been so bad, we could have gone out. (= we would have been able to go out)
* If the weather hadn’t been so bad, we might have gone out. (=perhaps we would have gone out)