The document discusses the past perfect tense and its uses in English grammar. The past perfect tense is formed using had + past participle and expresses actions that were completed before something else in the past. It can indicate a completed action before another past action or a duration of time before another past event. Examples are given for the positive and negative forms of the past perfect tense.

1. Past perfect tense Subj + HAD + + Participle + Complements eg. I couldn’t open the door because I had forgotten the key!!! We couldn’t go to the concert because we had lost the tickets.