The past perfect simple tense is used to show that an action was completed before another action or time in the past.

Positive: subject + had + past participle
Negative: subject + had not + past participle
Question: Had + subject + past participle

Common uses:

1. To indicate that an action was completed before another action in the past

• I had finished my homework before I went to bed.
• He hadn’t prepared the food before his guests arrived.
• Had they left the party before we got there?

2. To describe a past event that happened at a specific time or over a specific period

• She had lived in New York for five years.
• They hadn’t known each other at high school.
• Had he played chess every day for a year?

3. To express a hypothetical situation in the past

• If I had studied harder, I would have passed the exam.
• If he hadn’t left when he did, he would have missed the train.
• Had they listened to my advice, they would not be in trouble now.