THE FORM

HAD + PAST PARTICIPLE

We use the verb had and the past participle for the past perfect. Let's see with the verbs  TO WORK (a regular verb) and  TO SEE (an irregular verb)

THE USES:

1.  We use the Past Perfect for an action taking place before a certain time in the past (putting emphasis only on the fact, not the duration). We are already talking in the past but we want to talk about an earlier past time.

Before I came to see you, I had spoken to your English teacher.

First I spoke to your English teacher [1], then I came to see you [2].

When I arrived at the office, I realised that I had forgotten my umbrella.

First I forgot my umbrella [1], then I arrived at the office [2].

The train had already left when we arrived at the station.

First the train left [1]  then we arrived at the station [2].

2.  We also use the Past Perfect after WHEN to show that something is completely finished.

When the children had done all their homework, they went to the garden to plan cricket.

3.  We also use the Past Perfect to talk about the past in conditions, hypotheses and wishes:

I would have helped her if she had asked me.

It was very dangerous. What if you had got killed?

I wish I hadn’t spent so much money on clothes last month.