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Why is Present Perfect used here? Thanks in advance!

https://www.englishforums.com/English/TwoQuestions/bpckqk/post.htm

#1

I have lost my glasses. I must have dropped it somewhere.

#2

I was surprised that Kate wasn't at meeting yesterday. She might not have known.

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Андрей КириловWhy is Present Perfect used here?
Андрей Кирилов#1 I have lost my glasses. I must have dropped it them somewhere.
#2 I was surprised that Kate wasn't at the meeting yesterday. She might not have known (about it).

They are not examples of the present perfect tense (except 'have lost'). They are modal perfect constructions (the second type described below).

MODAL + bare infinitive: can go, could go, will go, would go, may go, ...
MODAL + "HAVE" + past participle: must have gone, would have gone, ...

Modal perfect constructions express past time.

I (have) lost my glasses. (implies past time)
I must have dropped them somewhere. (implies past time)
Paraphrases: It must be the case that I dropped them somewhere; The only deduction that it is reasonable to draw is that I dropped them somewhere.

I was surprised that Kate wasn't at the meeting yesterday. (implies past time)
She might not have known (about it). (implies past time)
Paraphrase: Maybe she did not know about it.


Contrast: I must drop them somewhere. (implies present and future time)
Contrast: She might not know (about it). (implies present time)

CJ

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Андрей КириловWhy is Present Perfect used here?

Present perfect is used for past events that are of significant interest to the discussion at hand.

But these examples were not submitted by a native speaker, so they are slightly unnatural.


These are more native:

I lost my glasses. I must have dropped them somewhere.
I was surprised that Kate wasn't at meeting yesterday. She might not have known about it.
I was surprised that Kate wasn't at meeting yesterday. We might have forgotten to include her on the invite list.