a. Some clauses with ‘if’, use past tense forms to talk about the present and future, for something that has not happened or is not happening. (e.g. He could get a new job if he really tried = He cannot get a job because he has not tried.)
b. We use the past tense forms to talk about the future in clauses with ‘if’, for something that we believe or know will not happen. (e.g. We would go by train if it wasn’t so expensive = We won’t go by train because it is too expensive)
c. and to make suggestions about what might happen. (e.g. If he came tomorrow we could borrow his car.)
d. When we are talking about something which did not happen in the past we use the past perfect in the ‘if clause’ and a ‘modal verb’ in the main clause. (e.g. If you had seen him you could have spoken to him = You did not see him so you could not speak to him.)
e. If the main clause is about the past we use a modal with have. (e.g. If you had seen him you could have spoken to him. = You did not see him so you could not speak to him.)
f. If the main clause is about the present we use a present tense form or a modal without have. (e.g. If I had got the job we would be living in Paris now. = I did not get the job so we are not living in Paris now.
Idioms
Saved by the Bell: Saved at the last possible moment.
Example: Luckily my bus arrived before I was freezing to death. Saved by the bell.