Formation:
Affirmative: (subject + had + been + verb+ing)
Negative: (subject + had+ not + been +
verb+ing)
Question: (had + subject + been + verb+ing)
Usage
The past perfect continuous certainly isn’t the most frequently used (or taught) tense in the English language but it does have one major use:
To talk about longer actions or situations in the past that had been going on continuously up to the past moment that we are thinking about. We don’t know or are not concerned with whether
or not it continued after.
E.g. Before eating lunch, she had been clipping her toenails for two
hours.
Common student mistakes/errors
As this
tense has two auxiliary verbs – ‘had’ and ‘been’ – the omission of either one of those or the failure to add ‘ing’ to the main form are the major errors with this structure. Some problems with
usage can also be expected as it can be easily confused with the past perfect (which stresses completed actions), and the past continuous. The latter implies
that the action happened around a time and not just up to
that time.