This formation means 'double past -- a time before another time in the past'. We use the past tense of the auxiliary verb have (Lesson 17) before the past participle (Lesson 14). Don't forget that many participles are irregular (Lesson 96).
They had all worked very hard that day.
She had gone by air to save time.
I hadn't put the address at the top.
NOTICE: There is also a continuous formation. The past participle is been and the -ing form follows:EXAMPLES:
NOTICE: Had can be an AUXILIARY and a LEXICAL verb (Lesson 3).
EXAMPLE: For three days, the men had not had any food.
When we got to the coast, they all cried out in surprise. It was the first time they had ever seen the sea.
We did not think we could win the match. Our best player had broken his leg in a car accident two days before.
The teams had been playing for ten minutes when the rain began.
NOTICE: We can use the past perfect to show which happened first:EXAMPLES:
I tried to open the door but somebody locked it from the other side.
[These two things happened at the same time.]