The past perfect progressive tense is used to describe an action that began in the past and continued up until another time in the past. It is formed using the past tense of "have" (had) plus the present participle of the verb (ending in -ing). This tense emphasizes the duration of an action that took place before another past event. It can also refer to a past action whose duration caused visible results at another point in time, such as being tired from cleaning all day. Time expressions like "before," "by the time," and phrases involving durations like "for" or "how long" are often used with the past perfect progressive.

1. S
Past
Perfect
Progressive

2. Structure (Form)
Structure
Auxiliary Verb: Had Been
Affirmative
Subject + Aux Verb + Verb -ING
I had been working
She had been sleeping
Negative
Subject + Aux Verb Not + Verb –ING
I had not been working
She had not benn sleeping
Question
(WH Question) + Aux Verb + Subject + Verb -ING
(When) Had you been working?
(Why) Had she been sleeping?

3. The Past Perfect Progressive is
used:
S To emphasize the duration
of an action that took
place before another
action in the past.
He had been living in
California for 15 years when
he moved to Boston.

4. S To refer to an action
whose duration caused
visible results at a later
point of time in the past.
S They were tired because
they had been cleaning
the house all day.

5. TIME EXPRESSIONS
Before + point in time
By + point in time
Before, After, When, By the time
How long, For, Since