Grammar study page: past perfect simple v past perfect continuous

Structure of past perfect
I'd (I had) seen him.	You hadn't (had not) seen him.	Had you seen him?

Structure of past perfect continuous
I'd (I had) been working hard.	I hadn't (had not) been working hard.	Had you been working hard?

Past perfect - common mistakes
Common mistakes	Correct version	Why?
I didn't been to London.	I hadn't been to London.	The helping verb had / hadn't is used in the past perfect.
When I saw him, I noticed that he had a haircut.	When I saw him I noticed that he had had a haircut.	The action (haircut) which happened before another past action must be put into the past perfect to make the time order clear to the listener.
He told me has been to London.	He told me he had been to London.	His original words were: ''I have been to London.'' However, in reported speech we move the tense back - the present perfect (have been) becomes past perfect (had been).

Past perfect continuous - common mistakes
Common mistakes	Correct version	Why?
I had working hard, so I felt very tired.	I had been working hard, so I felt very tired.	The form of the past perfect continuous is had + been + verb-ing.
I had been worked hard, so I felt very tired.
I had been hearing the song many times before.	I had heard the song many times before.	Some verbs are not normally used in the continuous form, e.g. stative verbs such as know, like, understand, believe, hear, etc.

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