Updated: Jun 28, 2020
This is one of the tenses that I feel shows one's ability to demonstrate a good grasp of the language. I like to call it the past of the past tense which means the action you are talking about happened before another action (both in the past). For example:
When I got home yesterday, I realised I had left my phone at my friend's house.
Here we have three actions and as a result three verbs. The first two are presented in chronological order so the past simple is used. When the third action is mentioned, then we need to show that it happened before the other two. That's when we need to use the past perfect.
Form: Pronoun (I/you/he/she/it/we/you/they) + had + past participle (affirmative)
Pronoun +had+ not + past participle (negative)
had +pronoun +past participle (question)
More examples: I hadn't seen this before yesterday (negative)
Had you seen this before yesterday? (question)
You should always use the past perfect when using the 3rd conditional:
If I had studied harder, I would have scored higher in the exam.
I hope these examples give you a clearer idea of when to use the past perfect and how.
Let me know if you need more examples, explanations or you just want me to post simpler rules on particular grammar points. You can also subscribe to receive extra English learning goodies straight to your inbox!