Present perfect vs simple past

[Tung Quoc]

Dear teachers,

Please read:

Yesterday was one of the coldest day that I have known.

1/I don't know the reason why the present perfect is used in this sentence. Please tell me this reason.

2/ If I write:
Yesterday was one of the coldest day that I knew.

Is it correct? If not (or yes), please tell me the reason.

Thanks
Quoc

[DOlier]

Hi Quoc

No 1 is correct becacuse you still know

No 2 would be correct if for example:
"He was a person I knew while at school, be I don't know him now".
If I still knew him I would say: "he is a person I have known since I was at school".

[Jamie (K)]