A past participle, by itself, cannot be the main verb of a sentence. When a past participle is combined with another verb, called a helping verb, however, it can be used to make the present perfect tense and the past perfect tense.
The present perfect tense is used for an action that began in the past and either continues into the present or was completed at some unknown time in the past.
My car has stalled several times recently.
The past perfect tense is used for an action that began and ended in the past before some other past action took place. It is formed as follows.
My head had ached for a week before I called a doctor. [Both of the actions (head ached and I called ) happened in the past, but the ache happened before the calling.]
Be careful not to confuse the simple past tense with the past perfect tense.
| SIMPLE PAST TENSE | My daughter left. [One action (the daughter leaving) occurred in the past.] |
| PAST PERFECT TENSE | By the time Jill arrived, my daughter had left. [Two actions (Jill’s arrival and the daughter leaving) occurred in the past, but the daughter left before Jill’s arrival.] |