What is different past perfect tense and future perfect tense?

Answer 1

Past Perfect TenseThis is used to express an action in the past before another action in the past. Both actions were completed some time in the past. It follows this structure:

• Subject + Had + Past Participle.

Future Perfect TenseThis talks about a point in future time, which is often indicated in the sentence with by. It is predicted that the action is completed by that time. The action may or may not have started in the past. It follows this structure:

• Subject + Will + Have + Past Participle.

So the difference is past perfect talks about actions that were completed (at time of talking) and future perfect talks about actions not completed (at time of talking)