Past perfect

Situation: Jack left his apartment at 2:00. Ann arrived at his apartment at 2:15 and knocked on the door.
(a) When Ann arrived, Jack wasn’t there. He had left.
The Past Perfect is used when the speaker is talking about two different events at two different time in the past; one event ends before the second event happens.
In (a): There are two events, and both happened in the past: Jack left his apartment. Ann arrived at the apartment. To show the time relationship between the two events, we use the past perfect (had left) to say that the first event (Jack leaving his apartment) was completed before the second event  (Ann arriving at this apartment) occurred.
(b) Jack had left his apartment when Ann arrived.
Form: had + past participle
(c) He’d left. I’d left. They’d left etc.
Contraction: They/We/I/Yoy/He/She/It +’d
Compare The Present And The Past Perfect
(d) I am not hungry now. I have already eaten
The Present Perfect expresses an activity that occurred before now, at an unspecified time in the past, as in (d)
(e) I was not hungry at 1:00 P.M. I had already eaten
The Past Perfect expresses an activity that occurred before another time in the past.
In (e): I ate at noon. I was not hungry at 1:00 P.M, because I had already eaten before 1:00 P.M
Compare The Past Progressive And The Past Perfect
(f) I was eating when bob came
The Past Progressive expresses an activity that was in progress at a particular time in the past.
In (f): I began eat at noon. Bob came at 12:10. My meal was in progress when Bob came.
(g) I had eaten when Bob came
The Past Perfect expresses an activity that completed before a particular time in the past.
In (g): I finished eating at noon. Bob came at 1:00 P.M. my meal was completed before Bob came.

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Present perfect progressive

Al and Ann are in their car right now. They are driving home. It is now four o'clock
(a) They have been driving since two o'clock
(b) They have been driving for two hours. They will be home soon.
The Present Perfect Progressive talks about how long an activity has been in progress before now.
Note: Time expression with since, as in (a), and for as in (b), are frequently ued with this tense. Statement: have/has+been+-ing
(c) How long have they been driving?
Question form: have/has+subject+been+-ing
Compare the present progressive and the present perfect progressive
Present progressive
(d) Po is sitting in class right now
The Preent Progressive describes an activity that is in progress right now, ax in (d). It does not discuss duration (length of time).
Incorrect: Po has been sitting in class right now.
Present perfect progressive
Po is sitting at his desk in class. He sat down at nine o'clock. It is now nine-thirty
(e) Po has been sitting in class since nine o'clock
(f) Po has been sitting in class for thirty minutes.
The Present Perfect Progressive expresses the duration (length of time) of an activity that began in the past and is in progress right now.
Incorrect: Po is sitging in class since nine o'clock
(g) Correct: I know Yoko
(h) Incorrect: I am knowing Yoko
(i) Correct: I have known Yoko for two years
(j) Incorrect: I have been knowing Yoko for two years
Reminder: Non-action verbs (e.g, know, like, own, belong) are not used in any progressive tenses.
In (i): With non-action verbs, the present perfect is used with since or for to express the duration of a situation that began in the padt and continues to the present.
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Using since and for

SINCE
(a) I have been here (since eight o'clock, Since Tuesday, Since May, Since 1999, Since January 3, 2001, Since yesterday, Since last month)
Since is followed by the mention of a specific point in time: an hour, a day, a month, a year etc.
Since expresses the idea that something begab at a specific time in the past and continues to the present.
(b) Correct: I have lived here since May
Correct: I have been here since May
(c) Incorrect: I am living here since May
(d) Incorrect: I live here since May
(e) Incorrect: I lived here since May
Incorrect: I was here since May
The present perfect is used in sentences with since:
In (c): The present progressive is NOT used
In (d): The simple present is NOT used
In (e): The simple past is NOT used
Main clause (present perfect)              Since clause (simple padt)
(f) I have lived here                           since I was a child
(g) Ali has met many people             since he came here
Since may also introduce a time clause (i.e, a subject and verb may follow since)
Notice in the examples: The Preent Perfect is used in the maim clause; the simple past is used in the since-clause
FOR
(h) I have been here (For ten minutes, For two hours, For five dsys, For about three weeks, For almost six months, For many years, For a long time)
For is followed by the mention of a lenght of time: two minutes, three hours, four dsys, five weeks etc.
Note: If the noun ends in -s (hours, days, weeks, etc.), use for in the time expression not since.
(i) I have lived here for two years. I moved here two years ago, and I still live here
(j) I lived in Athens for two years. I don' t live in Athens now.
In (i): The use of the present perfect in a sentence with for+a length of time means that the action began in the past and continues to the present.
In (j): The use of the simple past means that the action began and ended in the past.
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