Priority 1 · Verb frames
The auxiliary carries the time
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Earlier past — I had eaten before Jim came over.
Familiar activity — She is used to jogging. After to here, use -ing.
Planned requirement — The captain said we are to finish by next week.
Do not choose by sound; identify the time relationship first.
In a question, move the auxiliary before the subject: Had he been sleeping?
Grammar reference: Class 5 slides 27, 31, 34, and 37–40. “Had” extends the perfect frame into the past.