In and at

[Monica238]

Does either "in" or "at" work depending on whether I am speaking generally and thus use "at" or whether I am speaking about being inside and use "in"?

1. I eat at/in a restaurant every Sunday.

2 We were sitting in/at a restaurant when he called.

3. I often have lunch in/at a restaurant .

4. My parents work in/at the local university.

5. My brother is a chef in/at a restaurant.

 

[bennymix]

'In' and 'at' are pretty interchangeable in your examples, except possibly 4.

"at" followed by any structure (with an interior), such as a building, usually means 'in'.
"I'll meet you at the post office" suggests inside. For a clear reference to outside, you'd have to specify: "I'll meet you in front of the post office."

Of course, "I'll meet you at the corner" cannot be 'in', and one couldn't say 'in'.

 

[Monica238]

'In' and 'at' are pretty interchangeable in your examples, except possibly 4.

"at" followed by any structure (with an interior), such as a building, usually means 'in'.
"I'll meet you at the post office" suggests inside. For a clear reference to outside, you'd have to specify: "I'll meet you in front of the post office."

Of course, "I'll meet you at the corner" cannot be 'in', and one couldn't say 'in'.

But "I'll meet you in the post office" is also possible, isn't it?

 

[bennymix]

But "I'll meet you in the post office" is also possible, isn't it?

Yes. So, in some cases (for buildings, theaters, etc.) 'at' is ambiguous.