Past/Present tense in a conditional statement

Solution 1:

I'm afraid conditional sentences in English have nothing or next to nothing to do with the sequence of tenses in 'time line'.

a. When you're talking about some possibility in the future, you use present simple in conditional and future simple in main clause.

If you hand in your report tomorrow, the teacher will forgive you.

b. When you're talking about something, happening at the time of speaking, then you use past simple in the conditional and future-in-the-past in main clause. My English language teacher called this kind of conditional "next to impossible" - maybe, just maybe the conditional is fulfilled and the main clause then will take place.

If he handed in his report, the teacher would forgive him.

Meaning that he, whoever he is, can amend whatever transgression he made by handing in his report no later than the time I said this phrase.

c. When you're talking about something in the past, then you use past perfect in conditional and future perfect in main clause. By analogy, it's an "impossible" kind of conditional - something already didn't happen, but if it happened when it should have, then...

If he had handed in his report yesterday, the teacher would have forgiven him.

He didn't hand in his report in time, and lost any chance of being forgiven.