Using the past perfect tense
UsesThe past perfect tense is not usually used alone. It is mainly used with the simple past tense and then it refers to an action that has already happened by the time another action had commenced.
The patient had died before the doctor arrived. (NOT The patient died before the doctor had arrived.)
We use the past perfect tense for the earlier of the two past actions.
The train had left before we reached the station. (NOT The train left before we had reached the station.)
I had cooked the meals before the kids came home from school.
I had finished one project before I started the next.