# <Past perfect> and <simple past>

1. I left when he arrived.

Since we don't know how much time passed between the two actions, we could probably think the two action could happened at the similar time. So, we naturally think one action can affect the other, like I left because he arrived. The thing is he arrived first, and after that, I left.

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1. I left as he arrived.

I think this are the same as #1, but the time gap between the two action is only a very short, compared to #1. And like #1, he arrived first, and after that, I left.

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1. He arrived and I left.

I think it's like sequencing two different actions briefly so that speaker say something else, which would be actually what the speaker want to say.

1. I had left when he arrived.

"Past perfect" here is used to emphasize that one happened, and a while after that, the other happened So, the two action is not connected. We never know if I left because of him, .unlike #1,2 or 3.

By saying two "past perfect", the two actions are not connected. But, I can't think of any situation this is needed.

I think #1,2,3, are interchangeable in almost any case.

I'm sorry that I'm asking to many topics here, but I would only understand by comparing all of these.

1. I left when he arrived.

This means you left immediately after he arrived. You may have been waiting for him to arrive before you could leave, or it may have been a coincidence. But you did not start to leave until the very moment he arrived.

1. I left as he arrived.

This is not the same as #1. This means you left while he was arriving -- at the same time. For example, you may have been walking out the door just as he was walking in the door, but the two actions were happening at the same time.

1. He arrived and I left.

The order of events here is vague. Because of the order of the phrases, you could say he arrived first and then I left. But that's not necessarily the case. Because the two clauses are short, it's possible to infer that both actions happened at the same time.

Another possible interpretation is that I left because he arrived. It's impossible to draw this conclusion without more context, but this is a common way of communicating.

1. I had left when he arrived.

This means I was already gone before he even arrived.