Present Perfect or Simple Past?

UNIT 20 Present perfect (I have done) or simple past (I did)?

A.   It is often possible to use the present perfect (I have done) or the simple past (I did):

I've lost my key. Have you seen it anywhere?
or I lost my key. Did you see it anywhere?

But do not use the present perfect to say when something happened (for example, yesterday, two years ago, when I was a child, etc.). Use a past tense in these sentences:

• I lost my key yesterday. (not have lost)

• Did you see the movie on TV last night? (not have you seen)

• I ate a lot of candy when I was a child. (not have eaten)

Use a past tense to ask when or what time something happened:

• What time did they arrive? (not have they arrived)

• When were you born? (not have been born)

B.   Do not use present perfect (I have done) for happenings and actions that are not the connected with the present (for example, historical events):

• The Chinese invented printing. (not have invented)

• How many symphonies did Beethoven compose? (not has . . . composed)

C.   Now compare these sentences:
Present perfect (I have done)                                               Simple past (I did)
I've smoked 20 cigarettes today.                                       I smoked 20 cigarettes yesterday.

Today is a period of time that continues                           Yesterday is a finished time the
up to the present. It is not a finished                                   past. So we use the simple past.
time. So we use the present perfect.

Dan hasn't been sick this year                                           Dan wasn't sick last year.
Have you seen Ann this morning?                                    Did you see Ann this morning?                     (It is still morning)                                                                 (It is now afternoon.)
Have you seen Ann recently?                                             Did you see Ann last week?
We've been waiting for an hour. (We are                          We waited (or were waiting) for an
still waiting.)                                                                           hour. (We are no longer waiting.)
Pierre has lived in Quebec for six years                            Pierre lived in Quebec for ten years.
(He still lives there.)                                                              (He no longer lives there.)
I have never played golf (in my life).                            I didn't play golf when I was on vacation       .                                                                                                  last summer.

The present perfect always has a                                        The simple past tells us only about
connection with the present.                                                the past.