Verbs in time clauses and 'if' clauses

He could get a new job if he really tried.        (= He cannot get a job because he has not tried.)
If Jack was playing, they would probably win.
        (= Jack is not playing so they will probably not win.)
If I had his address, I could write to him.
        (= I do not have his address so I cannot write to him.)

We use past tense forms to talk about something that we believe or know will not happen in the future:

We would go by train if it wasn't so expensive.
       (= We will not go by train because it is too expensive.)
I would look after the children for you at the weekend if I was at home.
       (= I cannot look after the children because I will not be at home.)

We use past tense forms to make suggestions about what might happen in the future:

If he came tomorrow, we could borrow his car.
If we invited John, Mary would bring Angela.

After I/he/she/it, we can use were instead of was:

If Jack was/were playing, they would probably win.
We would go by train if it wasn't/weren’t so expensive.
I would look after the children for you at the weekend if I was/were at home.

We use the past perfect to talk about something which did not happen in the past:

If you had seen him, you could have spoken to him.
        (= You did not see him so you could not speak to him.)
You could have stayed with us if you had come to London.
        (= You could not stay with us because you did not come to London.)
If we hadn't spent all our money, we could take a holiday.
        (= We have spent all our money so we cannot take a holiday.)
If I had got the job, we would be living in Paris.
        (= I did not get the job, so we are not living in Paris.)

If the main clause of a hypothetical conditional is about the present or future, we use a modal:

If I had got the job, we might be living in Paris now.
        (= I did not get the job so we are not living in Paris now.)
If you had done your homework, you would know the answer.
        (= You did not do your homework so you do not know the answer.)

If the main clause is about the past, we use a modal with have: 

If I had seen him, I would have spoken to him.
       (= I did not see him so I did not speak to him.)
You could have stayed with us if you had come to London.
       (= You could not stay with us because you did not come to London.)
If you had invited me, I might have come.
       (= You did not invite me so I did not come.)

 

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