General Writing and Grammar Help/"in" and "at" in American and British English
Thank you very much for your detailed answer.
Now that you've mentioned the different usage(?) of "in" and "at" in American and British English, here's a question that I have been dying to ask an expert like you.
After I have lived in the US for years now, I am begining to notice that Americans use "at" in instances when I'd use "in". For instance, just today, I have received an email from an English teacher(American) confirming my enrollment in her conversation class. I'd like you to read the exchange of our emails:
My name is Carlie. I was in the INS(International Student's) office last week looking for a free conversation class and I learned about your conversation class. Is there room in your class? If there is, I would love to join in."
"Hi, Carlie. You are most welcome to join us at 5:30 p.m. every Monday here at the INS Office. I look forward to meeting you!
Notice how I used "in" and how she used "at". I was a bit confused that she used "at" in this instance. I used "in" because I was inside the office to look for something. And I think in this instance, an British person would say "in the office" too. What do you think?
Also, my feeling is that Americans most likely use "at" in instances when the British would use "in" like my email example.
You would never say in American English that some is a nurse "in hospital." Instead you would say "at a hospital." (In British English, however, they do say "in hospital," rather than "in the hospital" as we would say in the U.S.) In other situations, these guidelines don't apply at all, as "in your first/second example" in my answer above demonstrates. In short, as is the case with many prepositions in English, it depends a lot on what the object of the preposition is and the general meaning or subject of the sentence.
Sorry I haven't answered this question sooner, but I had to give it some thought. In many cases "in" or "at" can be used interchangably with no difference in meaning, especially with "the office." The way you use "in the office" in this example is fine, and your reason for using it makes sense. However, you could just as well say "at the office" in that situation. "At" is often used to a something as a place, a location, perhaps some sort of institution, such as at the theater, at the library, at the restaurant, at the office. You could use "in" with most of these nouns, too, to convey the idea of being INSIDE that place.
There are more subtle idiomatic expressions and situations for each of these nouns than I could begin to explain. ("I was at the library when I found the book" "The book was in the library" "We met at the library" "We met in the library" are all correct and just a few examples.) But I think, on the whole, more often than not, you might use either "at" or "in" in most situations involving these sorts of nouns. It depends somewhat on a person's preference and habit, but you probably have some sense of when you are talking about something "in" (inside) a place or "at" a place ("at" a location).
However, the second sentence, the woman's response, is one case where I think there would be a preference; it would be preferable and more natural to say "at the office" in this case because of "welcome." There's a sense that it's "the office" that is "welcoming" you, and so it makes sense to refer the office as a place, a location, using "at," rather than to think of it as a place to be "inside." On the other hand, one might say "You are not welcome in this house." There's a territorial feeling about this expression: within these boundaries. But one might be at least as likely to say "You ARE welcome AT this house."