Past Perfect Continuous

1. Definition & Core Meaning
The Past Perfect Continuous Tense describes an action that was going on for a period of time in the past before another past event interrupted it.

2. Use Cases - Why do we use it?
• Duration Before a Past Event: Showing how long something was happening up to a point in the past. I had been waiting for two hours before the bus finally arrived.
• Cause of a Past Situation: Explaining why a past state existed. The grass was wet because it had been raining all night.

3. When to Use It - Key Signals
Look for duration combined with a past marker: for [time] when/before...

4. How to Use It - Structural Formula
(+) Affirmative:
• Subject + had been + verb-ing --> She had been trying.

(-) Negative:
• Subject + had not been (hadn't been) + verb-ing --> They hadn't been studying.

(?) Question:
• Had + Subject + been + verb-ing? --> Had you been sleeping when I knocked?