ref –
- https://www.youtube.com/watch?v=lzsdrz2QtcM&t=129s
- https://www.espressoenglish.net/difference-between-present-perfect-and-past-perfect-in-english/
- https://www.natterandramble.co.uk/past-perfect-tense-timeline-form-uses/
Past Perfect, shows that a past action that happened earlier than another past action. It’s a one time occurrence.
In other words, both actions happened in the past. One past action happened before another past action.
Subj + had + [past participle]
The past perfect, also called the pluperfect, is a verb tense used to talk about something that happened before something else that is also in the past.
Imagine waking up one morning and stepping outside to grab the newspaper. On your way back in, you notice a mysterious message scrawled across your front door: “Tootles was here.” When you’re telling this story to your friends later, how will you describe this moment? You might say something like:
I turned back to the house and saw that someone named Tootles (had) [defaced my] front door!
Your friends will able to understand that:
1) Tootles graffitied the door at some point in the past before
2) the moment this morning when you saw their handiwork
Past—Tootles graffitied your door—You saw his handiwork—Now
Consider the difference between these two sentences:
We were relieved that Tootles used washable paint.
We were relieved that Tootles had used washable paint.
It’s a subtle difference, but the first sentence doesn’t tie Tootles’s act of using washable paint to any particular moment in time; listeners might interpret it as “We were relieved that Tootles was in the habit of using washable paint.”
In the second sentence, the past perfect makes it clear that you’re talking about a specific instance of using washable paint.
Another time to use the past perfect is when you are expressing a condition and a result:
If I had woken up earlier this morning, I would have caught Tootles red-handed.
The past perfect is used in the part of the sentence that explains the condition (the if-clause).
ex:
* she arrived at the office
* she realized it was Sunday.
She had arrived at the office before she realized it was Sunday.
ex:
* I ran to my car
* I noticed my wife left.
I ran to my car when I noticed my wife had left already.
ex:
* Sofie finished her work.
* Sofie then went to lunch.
After Sofie had finished her work, she went to lunch.
Other examples
What is difference between usage of [before] and [when]?
https://www.oxfordlearnersdictionaries.com/grammar/online-grammar/past-perfect-simple-with-time-expressions
when
We use when + past perfect to talk about an action that happened immediately before something else.
When we’d done the washing-up, we watched TV.
(We did the washing-up, and then we watched TV.)
we can use when + past simple to talk about an action that happened after something else.
When I phoned the office, Emma had already left.
(Emma left the office, and then I phoned.)
before
We can use before with past simple OR past perfect to talk about an action that happened before something else.
We arrived just [before] the plane doors closed.
We [arrived] before the plane doors had closed.