Conditions, Past Unreal

In a past-unreal condition, the past perfect tense of the verb is used in the if clause and would have (should have, could have, might have ) is used in the main or answer clause.

Examples:

If I had known Helen's number, I would have called her.

If John had had the time yesterday, he would have gone with us.

Note again that past-unreal conditions, just like present-unreal conditions, always describe a hypothetical, "unreal," or contrary-to-fact situation. Thus:

I didn't know Helen's number, but-if I had known it, I would have called her.

John didn't have time yesterday, but-if he had had time, he would have gone with us.