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Sir,

Adverb of past cannot be used with persent perfect tesnce as stated in a grammar book.

But,

1.I have not seen him since last week.

"last week" is adverb of past time. Why "last week" has been used here?

2.I have not seen hims since yesterday.

"yesterday" is also adverb of past time. Can we use it like this.

3. I have not met hims for a week.

4. I have not met him a week ago.

The (3) one seems correct. But (4) I have used "a week ago" . Is it possible to use "a week ago" or "a few years ago" in persent perfect tense.

Please help me,I am in big problem concerning to adverb of past time used in persent perfect tense.

Thanks.
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(1) and (2) are fine, Hanuman. They are not adverbs, they are noun objects of the preposition 'since'; the whole prepositional phrase serves as an adverbial. They represent, as I am sure you can see, the extent of time after last week and yesterday, respectively, not those expired time frames themselves.

(3) is correct for the same reason, but (4) is indeed wrong-- 'ago' is your adverb of past time, which does not mesh with present perfect unless it is part of a prepositional phrase: 'I have not met him since a week ago'.
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Sir(Mister Mcawber),

I am really thankfull to you for your excellent explanation.

I have still some doubts.Could you please help me?

1.I have not met him for a weak ago.

2.I have not met him since aweak ago.

Somebody told me (1) is not correct because there is no "for NP ago" construction.

I could not understand becuase if we can say "I have not met him for a weak.";then why not
"I have not met him for a weak ago".

Please explain the difference between "for a weak" and "for a weak ago".

Is (2) is coorect?

Thanks.
Only (2) is correct, Hanuman-- if you spell 'a week' correctly.

'A week ago' is a point in time; it is the same as 'last Monday' (today being Monday here now). 'A week', on the contrary, is a span of time; it exhibits 'duration'; 'a week' is two-dimensional, where 'a week ago' is one-dimensional, temporally speaking.

'For + time unit' is also a span of time, measuring an activity: 'I waited for 10 minutes'-- the waiting time was for (equal to) a span of ten minutes.

'Since + time unit + ago' is a point in time, pinpointing the location of an activity in time:
'I haven't seen him since a week ago'-- this is NOT measuring the span between last Monday and today, it is indicating the last time point at which 'he WAS seen'.

The mixed-up versions (X 'for a week ago' and X 'since a week') are grammatical errors and carry no meaning.
Sir,

I am amazed with your way of teaching. once again thanks.
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