The "Past Before the Past"
Use Past Perfect (had + past participle) to show that one action happened BEFORE another past action.
Timeline:
Past Perfect Action -> Simple Past Action -> NOW
Unreal Past:
Past Perfect is also used to talk about imaginary situations in the past (regrets):
ā¢ After wish (I wish I had studied harder)
ā¢ After if only (If only I had known!)
ā¢ In Third Conditionals (If I had seen him, I would have said hello)
Example: When I arrived (Simple Past), the train had already left (Past Perfect - happened first).