|Unfinished actions that started in the past and continue to the present:I’ve known Julie for ten years (and I still know her).
||Finished actions:I knew Julie for ten years (but now we are no longer in contact).
|A finished action in someone’s life (when the person is still alive: life experience):My brother has been to Mexico three times.
||A finished action in someone’s life (when the person is dead):My great-grandmother went to Mexico three times.
|A finished action with a result in the present:I’ve lost my keys! (The result is that I can’t get into my house now).
||A finished action with no result in the present:I lost my keys yesterday. It was terrible! (Now there is no result. I got new keys yesterday).
|With an unfinished time word (this week, this month, today):I’ve seen John this week.
||With a finished time word (last week, last month, yesterday):I saw John last week.