Grammar Focus: Past Perfect Continuous

The Past Perfect Continuous describes an action that started in the past and continued up to another point in the past. Form: had + been + verb-ing.

• Duration before a past point: Miller had been working on the case for weeks (before the breakthrough).

Simple vs. Continuous: Simple = a completed action before another past action (I had finished my homework before I went out); Continuous = the duration of an action up to a past point (I had been doing my homework for two hours before I went out). Time words: for, since, all day, before, by the time.