|I had worked.||Had I worked?||I had not worked.|
|She had played.||Had she played?||She had not played.|
|It had rained.||Had it rained?||It had not rained.|
|They had waited.||Had they waited?||They had not waited.|
|You had promised.||Had you promised?||You had not promised.|
As you can see in the past perfect tense, the auxiliary verb had is used with both singular and plural nouns.
The past perfect tense is not usually used alone. It is mainly used with the simple past tense and then it refers to an action that has already happened by the time another action had commenced.
- The patient had died before the doctor arrived. (NOT The patient died before the doctor had arrived.)
We use the past perfect tense for the earlier of the two past actions.
- The train had left before we reached the station. (NOT The train left before we had reached the station.)
- I had cooked the meals before the kids came home from school.
- I had finished one project before I started the next.
In many cases we can use time conjunctions like before and after to indicate that one action had taken place before another commenced. The use of past perfect tense is optional in this case. That means you can use it but it is not necessary.
- After he finished the project he went to Australia for a month. OR
- After he had finished the project he went to Australia for a month.
Note that the past perfect tense is only used as described above. It is not used to simply say that something happened some time ago.
- I met an old friend of mine yesterday. (NOT I had met an old friend of mine yesterday.)