Prepositions "in" vs. "at"

[Rache]

I am having some problems with these prepositions, in and at. Is it possible to say both "I am at the library" or "in the library"? Is there a change in the meaning? Can you use either of them no matter what the place you are referring to is?
Thanks for your help!

 

[Anglika]

I am at the library - you could be either outside the library building or in the library building. It is not clear.

I am in the library - you are inside the library building.

 

[jctgf]

I am at the library - you could be either outside the library building or in the library building. It is not clear.

I am in the library - you are inside the library building.

hello anglika,

so, the idea behind "at" and "in" is always that?

may i apply this rule for every situation?

thanks

 

[Anglika]

hello anglika,

so, the idea behind "at" and "in" is always that?

may i apply this rule for every situation?

thanks

In this context, yes.

It is not a rule for every situation.

The hands of the clock are set at midday
The day ends at sunset


I am in a hurry
You will be found in a moment.

 

[Borovac]

I am at the library - you could be either outside the library building or in the library building. It is not clear.

I am in the library - you are inside the library building.

I found these examples on the internet:
I usually study at the library til 2am
They would come from the other universities to study at the library at Saint Mary's

If it's sais this is it grammatically incorrect or only not precise? Would people understand where the person is and consider it right or not?

thank you very much!

 

[Anglika]

English is a flexible and subtle language, which is why it can be so exasperating for non-native speakers.

Both your examples are fine - in the context in which they are used. They are acceptable and comprehensible. We would understand that the person is both at and within the library.