"Mr. Dill works ________ a big library" [closed]

I'd appreciate a clarification on when it would be best to complete this sentence with "at" and when with "in".

Solution 1:

Whether you should say “Mr. Dill works at a big library” or “Mr. Dill works in a big library” depends on what the facts are and your intended emphasis. If Mr. Dill is a librarian who works inside the library, either form can be used with little difference in meaning and no difference in grammaticality. If Mr. Dill is a groundskeeper who works for the library but outside it, I'd say at, not in, because it is misleading to say that he works in the library.

In the example sentence, you can use any of the prepositions at, in, or for, with the same meanings for most employees. If you want to emphasize who Mr. Dill works for, use for or at, not in. If you want to emphasize where Mr. Dill works, use in, inside, or outside.