When To Use The Past Perfect Tense

Traditional grammarians have always maintained that the past perfect tense must be used when the time of one past action is more past than that of another.

Suddenly I realized that I had seen him last year. (NOT Suddenly I realized that I saw him last year.)
I could not see him because he had gone out before I arrived. (NOT I could not see him because he went out before I arrived.)
There I met a man who had been my neighbor 20 years ago. (NOT There I met a man who was my neighbor 20 years ago.)

Special cases

Sometimes we can use time conjunctions (e.g. before, after, when, while, as soon as, no sooner etc.) to talk about two actions or events that happen one after the other. Usually the past perfect tense is not necessary in these cases, though it can be used.

After he had finished school, he went to London. OR After he finished school, he went to London.
He had gone out before I arrived. OR He went out before I arrived.
As soon as she had finished her book on African history, she started working on another. OR As soon as she finished her book on African history, she started working on another.

Though the past perfect tense is not necessary in these sentences, it is used when we want to emphasize the idea of completion.

Cases where the past perfect tense is not possible

The past perfect tense is not used when the first action 'leads into' the other or when there is a cause-and-effect relationship between the two actions. In such cases we use two simple past tenses.

When I opened the door I saw a strange sight. (More natural than When I had opened the door, I saw a strange sight.)

Here two simple past tenses are used because there is a cause-and-effect link between the two actions: I wouldn't have seen the strange sight if I hadn't opened the door.

When I called her, she came at once. (NOT When I had called her, she came at once.) Here the first action leads into the second.
When I opened the window, the cat jumped out. (NOT When I had opened the window, the cat jumped out.)

Past perfect tenses are normally only used as described above. The past perfect is not used simply to say that something happened some time ago.

Mrs. Fernandez, who taught classical music at the academy for twenty years, is now living in retirement. (NOT Mrs. Fernandez, who had taught...)
I forgot to take my umbrella. (NOT I had forgotten to take my umbrella.)
She bought some meat. (NOT She had bought some meat.)

Manjusha Nambiar is an ESL tutor and content developer. Her site perfectyourenglish.com gives English Speaking and English Grammar lessons. Subscribe to her feed and you will win a free Grammar eBook titled '120 Grammar and Vocabulary Mistakes to Avoid'.