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While I know very well the difference between "on" and "in", or even between "on" and "above", I didn't get what the difference between "in" and "at" is, that many specific things strictly get just one of them (such as "at the university", "in the building", "in / at the morning".).

Is there a clear rule where to use this one (at) and where to use the second one (in)?

marked as duplicate by Nathan Tuggy, laugh, Andrew, JavaLatte, kiamlaluno Dec 26 '17 at 13:50

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  • I'm afraid not; you'll have to learn all those things on a case-by-case basis. "At the morning" is not correct, but I couldn't tell you why. That's just the way it is. – Mr Lister Dec 18 '17 at 16:20
  • @MrLister Morning is an extended period of time, so we use in; whereas noon is a specific time, so we use at. You are right, though. There is no general rule. – Mick Dec 18 '17 at 16:49
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The main difference between "in" and "at" in everyday speech and locating people or things geographically is this:

if a person or thing is at some place, it does not mean they are necessarily in it.

  • John's at home right now playing with his children outside.

    The preposition at is used to describe the fact of a person or thing being at a geographical location but does not describe the person or thing actually being inside of the structure or place.

  • John is at home but he is not in(side) his house. He's in the garden at the moment.
  • When people are at home they are either inside their house or apartment but could be on the porch or veranda or in the garden.

If a person or thing therefore is at a place, they can also be inside some structure there: in the building, in the house, in the store, in the garden, in the park (considered to be a structure, semantically).

Bear in mind also that to be "in(side) a place or location" does not mean the place or location has to be covered: to be in the garden (gardens are generally open air), to be in the parking lot, to be in the woods. These places are considered to be places you can be in.

Finally, there are also idiomatic uses of in which means to be attending: to be in school or class (studying at a college or university); to be in church; to be in court These usages mean: to be attending school or church or court. Also, or to be institutionalized is: to be in hospital (BrE) and to be in the hospital (AmE). To be in the loony bin. :)

This should get you started but will not, by any means, cover every case.

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The prepositions in and at can have many different functions. Sometimes there is no logical reason related to why we use one preposition and not another. Practice and experience will help you.

Generally speaking at is used to describe an exact location or time.

E.g. I will meet him at 2pm. ** ** = the time stated is very exact or specific**.**

E.g. I will meet you at the library. = the exact place you will meet.

You can also use at to describe where two lines cross or intersect such as two roads that cross or a corner.

E.g. I will meet you at highway 1. and Corfield St. = where these two roads cross each other.

E.g. Meet me at the corner of Corfied road and Murray St.= where these two streets connect or join at a corner.

We can also use in to talk about time and place.

E.g. I will see him in January.

E.g. I will see him in the new year .(or in 2018).

E.g. Put the piano in the corner. = used to show a specific location within a house.

E.g. Please meet me in the library. = in refers to inside the library and at generally refers to meeting outside at the entrance (although English speakers can use both to mean the inside).

As you can see, some of these functions are logical while others have to be committed to memory. These are only a few uses and examples.

Also remember that some prepositions form part of a phrasal verb structure and don't function on their own and this confuses learners.

E.g. Please drop in when you have time. drop in = please visit

  • I tried to address location; and you address time, also. Rome was not built in a day. But, I think one can come up with general rules. – Lambie Dec 18 '17 at 17:35
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AT

*AT describes position at a specific point. It's very cold at the bottom of the ocean.

*AT is also used with a larger place (a store, bank, airport etc) Let's meet at the bank

*AT is used before the names of group activities at a party, at a meeting, at a play, at a parade

IN

*IN refers to position within large areas or in spaces that surround something on all sides My keys are in my bag. He is not in his office. The car is in the garage

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