We use the past perfect to show that one past event happened before a second past event.
We make it with the helping verb had + the past participle of the verb (Verb 3).
What had you done by the time you took the train?
- I had already eaten by the time I took the train to school.
- I had already made my breakfast, by the time I got on the train.
What had you done by the time you went to class?
- I had already taken the train before I went to class.
- I had already finished my commute before class began.
What had he done by the time he started university?
- He had already grown up before he started university.
- He had already turned 18 before he began university.
What had he done by the time he graduated university?
- He had already graduated by the time he found a job.
- He had finished school before he began working.
To make this for negative, just follow the helping verb with “not.”
What hadn’t he done by the time he finished university?
- He had not found a job. (You can also say: He hadn’t yet found a job.)
- He hadn’t yet gotten married. He hadn’t yet had kids.