Verb tenses take on many different combinations, and the past perfect tense is one of them. And much like the other tenses of verbs, there are certain rules to follow when it comes to its proper use. These are:
Follow the past perfect format.
Each verb tense has a specific function and a corresponding format. When it comes to the past perfect tense, you combine the word had with the verb’s past participle.
For example, if you want to express the verb study in its past perfect tense, you simply transform it to its past participle form (studied) and add the word had before it.
Simply put: had + verb’s past participle = past perfect tense.
Following this format, you will get: had + studied = had studied.
Convey the sequence of events.
The past perfect tense of a verb is used to show that something happened before another action or event. For example, if you want to use the past perfect tense had studied to express that the act of studying happened before another thing, you can say:
Liz had studied day and night before she took the mock exams.
Express conditions and results.
Another use of the past perfect tense is when you have an if-clause in the sentence. From the given example, if you want to denote that the act of studying is a pre-condition that leads to a certain result, you can express it as:
If Liz had studied regularly, she would have passed the mock exams with flying colors.