When to use perfect progressive tenses?

Answer 1

A perfect progressive tense is used to signify an action which was continuing at some time in the past or is expected to be continuing at some time in the future. If the time in the past was a substantial time in the past, the past progressive tense should be used. For example, "Until the passage of the Reform Bill in 19th Century England, many people had been continually grumbling about the inequities of representation in Parliament." If the action can have been continuing until the moment of speaking or writing, the present perfect progressive tense should be used. For example, "You have been grumbling all morning, and I'm tired of listening to you!" If the action is being forecast to continue until some time in the future, the future perfect progressive should be used. For example, "Until the end of time, some people will have been complaining about their undeserved obscurity."