Past Perfect

1) Form:
The past perfect is constructed by "had" and the verb' s past participle:
had + past participle

a) All forms:
- Positive:
I had eaten.
You had eaten.
He had eaten.
She had eaten.
It had eaten.
We had eaten.
You had eaten.
They had eaten.

- Negative:
I had not eaten.
You had not eaten.
He had not eaten.
She had not eaten.
It had not eaten.
We had not eaten.
You had not eaten.
They had not eaten.

- Question:
Had I eaten?
Had you eaten?
Had he eaten?
Had she eaten?
Had it eaten?
Had we eaten?
Had you eaten?
Had they eaten?

- Passive (positive / negative / question):
It had been eaten.
It had not been eaten.
Had it been eaten?

b) Examples for sentences with the past perfect:
I had married my wife before I finished college.
You had lived in the Unites States before you moved to the United Kingdom.
He had not met his wife before he went to the United States to work.
We had not called Grandma before she left for Italy.
Had you ever lived in Italy before you moved to Milan last year?
Had they studied fine arts before they applied for an internship with the Museum of Fine Arts?
John had repaired many used cars before he opened his own car repair shop. (Active)
Many used cars had been repaired by John before he opened his own car reparir shop. (Passive)

2) Use:
There are two uses for the past perfect: First, to describe a completed action before another action took place in the past. And second, to describe a duration in the past that lasted until another action began.

a) Completed event before another event in the past:
In this case, the past perfect is employed to express the idea that one event occurred before another event in the past or that an event took place before a precise moment in the past.

- Examples:
I had never been to such a fine restaurant before Miguel invited me to "La Bouche d' Or".
You did not have any money left because a pickpocket had stolen your wallet.
He knew Berlin so well because he had lived there for many years.
She had never studied German before she moved to Frankfurt.
We had rarely missed an opportunity to watch the home games of our local soccer club before 2010.
Had you never been to an opera before last week' s premiere?
Were they not able to get a hotel room because they had not booked in advance?

b) Duration before an event in the past:
In this case (which only applies to non-continuous verbs as well as the non-continuous uses of some mixed verbs), the past perfect is employed to express that an action has started in the past and lasted until another action began.

- Examples:
I had rented the house for ten years before we had to move out.
All week, you had promised me to go shopping with me before you suddenly called off the appointment.
By the time he finished his studies, he had been in Munich for over seven years.
We did not feel bad about selling the house because we had only owned it for about a year.
You did not move to Athens because you had been there earlier and did not like it.
They never apologized after they had insulted me.

3) Notes:
a) Specific time words or time clauses can be used with the past perfect (as opposed to the present perfect).

- Examples:
I had never been to Manchester in the 1990s before I moved there in 2000.
You had never missed a game of your favourite team in the 1999/2000 season until you moved to Germany in May 2000.

b) Instead of the past perfect, the simple past can be employed to describe an action that occurred at a precise moment in the past when either "before" or "after" are used, as both of these words already indicate which of the two actions took place first.

- Examples:
RIGHT: He had visited his German relatives twice in 2005 before he moved in with them in 2006. (Past perfect)
RIGHT: He visited his German relatives only twice in 2005 before he moved in with them in 2006. (Simple past)

If however the action in the past perfect is not referring to a specific time, it' s use is not optional, and the simple past cannot be employed instead, as in these cases, the use of past perfect rather indicates a general lack of experience in the past rather than a specific action at a precise moment in the past.

- Examples:
WRONG: He never saw a tiger before he moved to India. (Simple past)
RIGHT: He had never seen a tiger before he moved to India. (Past perfect)

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