I've stumbled across the following rule in the grammar book 'My Grammar Lab': with before + past perfect the action in the past simple happens first. The following example has been given: I left university before I'd finished the course. In this very book I've also found the following sentence 'All the leaves had fallen from the trees before we arrived', which doesn't follow this rule.
I've also found these two sentences in the Cambridge dictionary:
- Before I had a chance to thank him, he’d gone.
- Before he had finished his training, he was sacked.
In the first sentence the past perfect tense has been used for the earlier action and in the second sentence the past simple tense has been used for the earlier action.
As far as I know, we usually use the past perfect for the earlier action and the past simple for the later one, so I'm really confused about the correct way of using 'before' with the past perfect tense.
Could you please tell me if there is a clear rule regarding this case?
Thank you in advance.