Ann is looking for her key. She can’t find it.
She has Lost her key. (present perfect)
This means that she doesn’t have her key now.
Five minutes later:
Now Ann has found her key. She has it now.
Has she lost her key? No, she has found it.
Did she Lose her key? Yes, she did.
She lost her key (past simple)
but now she has found it. (present perfect)
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The present perfect (something has happened) is a present tense. It always tells us about the situation now. ‘Ann has lost her key’= She doesn’t have her key now
The past simple (something happened) tells us only about the past. If somebody says ‘Ann lost her key’, this doesn’t tell us whether she has the key now or not. It tells us only that she lost her key at some time in the past.
Do not use the present perfect if the situation now is different.
They’ve gone away. They’ll be back on Friday. (they are away now)
They went away, but I think they’re back at home now. (not They’ve gone)
It has stopped raining now, so we don’t need the umbrella. (it isn’t raining now)
It stopped raining for a while, but now it’s raining again. (not it has stopped)
You can use the present perfect for new or recent happenings:
‘I’ve repaired the washing machine. It’s working OK now.’ ‘Oh, that’s good.’
‘Ann has had a baby! It’s a girl.’ ‘That’s great news.’
Usually, you can also use the past simple:
I repaired the washing machine. It’s working OK now.
Use the past simple (not the present perfect) for things that are not recent or new:
Beethoven was a composer. He wrote more than 200 pieces of music.
(not has been … has written)
My mother grew up in France. (not has grown)
Did you know that somebody has invented a new type of washing machine?
Who invented the telephone? (not has invented)
We use the present perfect to give new information. But if we continue to talk about it, we normally use the past simple:
K: Ow! I’ve burnt myself.
D: How did you do that? (not have you done)
K: I picked up a hot dish. (not have picked)
K: Look! Somebody has spilt something on the sofa.
D: Well, it wasn’t me. I didn’t do it. (not hasn’t been … haven’t done)