Unit 13. present perfect and past (1) (i have done and i did)

A. Study this example situation:
Tom is looking for his key. He can't find it.
He has lost his key. (present perfect)
This means that he doesn't have his key now.

Ten minutes later:
Now Tom has found his key. He has it now.
Has he lost his key? (present perfect)
No, he hasn't. He has found it.
Did he lose his key? (past simple)
Yes, he did.
He lost his key (past simple)
but now he has found it. (present perfect)
The present perfect is a present tense. It always tells us something about now. 'Tom has lost his key' = he doesn't have his key now (see Unit 7).
The past simple tells us only about the past. If somebody says 'Tom lost his key', we don't know whether he has it now or not. We only know that he lost it at some time in the past.
Two more examples:
* Jack grew a beard but now he has shaved it off. (so he doesn't have a beard now)
* They went out after lunch and they've just come back. (so they are back now)
B. Do not use the present perfect if there is no connection with the present (for example, things that happened a long time ago):
* The Chinese invented printing. (not 'have invented')
* How many plays did Shakespeare write? (not 'has Shakespeare written')
* Beethoven was a great composer. (not 'has been')
* Shakespeare wrote many plays.
* My sister is a writer. She has written many books. (she still writes books)
C. We use the present perfect to give new information (see Unit 7). But if we continue to talk about it, we normally use the past simple:
* A: Ow! I've burnt myself.
B: How did you do that? (not 'have you done')
A: I picked up a hot dish. (not 'have picked')
* A: Look! Somebody has spilt milk on the carpet.
B: Well, it wasn't me. I didn't do it. (not 'hasn't been … haven't done')
A: I wonder who it was then. (not 'who it has been')