Past Perfect

[had + past participle]

Examples:

You had studied English before you moved to New York.
Had you studied English before you moved to New York?
You had not studied English before you moved to New York.

Complete List of Past Perfect Forms
USE 1 Completed Action Before Something in the Past

The
Past Perfect expresses the idea that something occurred before another
action in the past. It can also show that something happened before a
specific time in the past.

Examples:

I had never seen such a beautiful beach before I went to Kauai.
I did not have any money because I had lost my wallet.
Tony knew Istanbul so well because he had visited the city several times.
Had Susan ever studied Thai before she moved to Thailand?
She only understood the movie because she had read the book.
Kristine had never been to an opera before last night.
We were not able to get a hotel room because we had not booked in advance.
A: Had you ever visited the U.S. before your trip in 2006?
B: Yes, I had been to the U.S. once before.

USE 2 Duration Before Something in the Past (Non-Continuous Verbs)

With
Non-Continuous Verbs and some non-continuous uses of Mixed Verbs, we
use the Past Perfect to show that something started in the past and
continued up until another action in the past.

Examples:

We had had that car for ten years before it broke down.
By the time Alex finished his studies, he had been in London for over eight years.
They felt bad about selling the house because they had owned it for more than forty years.

Although
the above use of Past Perfect is normally limited to Non-Continuous
Verbs and non-continuous uses of Mixed Verbs, the words "live," "work,"
"teach," and "study" are sometimes used in this way even though they are
NOT Non-Continuous Verbs.
IMPORTANT Specific Times with the Past Perfect

Unlike
with the Present Perfect, it is possible to use specific time words or
phrases with the Past Perfect. Although this is possible, it is usually
not necessary.

Example:

She had visited her Japanese relatives once in 1993 before she moved in with them in 1996.

MOREOVER

If
the Past Perfect action did occur at a specific time, the Simple Past
can be used instead of the Past Perfect when "before" or "after" is used
in the sentence. The words "before" and "after" actually tell you what
happens first, so the Past Perfect is optional. For this reason, both
sentences below are correct.

Examples:

She had visited her Japanese relatives once in 1993 before she moved in with them in 1996.
She visited her Japanese relatives once in 1993 before she moved in with them in 1996.

HOWEVER

If
the Past Perfect is not referring to an action at a specific time, Past
Perfect is not optional. Compare the examples below. Here Past Perfect
is referring to a lack of experience rather than an action at a specific
time. For this reason, Simple Past cannot be used.

Examples:

She never saw a bear before she moved to Alaska. Not Correct
She had never seen a bear before she moved to Alaska. Correct

ADVERB PLACEMENT

The examples below show the placement for grammar adverbs such as: always, only, never, ever, still, just, etc.

Examples:

You had previously studied English before you moved to New York.
Had you previously studied English before you moved to New York?

ACTIVE / PASSIVE

Examples:

George had repaired many cars before he received his mechanic's license. Active
Many cars had been repaired by George before he received his mechanic's license. Passive