"at", "in", and "on"

Some of the usage is irregular... we ride "in" a train but "on" a bus; "in" a car and "on" a bike.

Do you have some examples about problems with "at"? I guess you already know it is used to refer to a location or time.

Well they all have different meanings, but the meanings are similar.

At-->this refers to some geographical location. Whether it be a park, concert, city, or house. It will refer to a location.
example: "I want to be at the concert" "I don't like sitting at the table"

Both "in" and "on" can take on a few different meanings, one of which deals with geography.

In--> Being "in" something means you are presently occupy some amount of space at a location. Not only are you "at" the location, but you are inside the location.
Example: "I'm in the kitchen. (It means you are physically in the space where the kitchen exists"
"I'm in the box" (It means not only are you "at" the box (in the same region), but you are being more specific by saying you are physically in the box. You are in the space which the box occupies.


On--> Being on something is just putting yourself on top of the OBJECT. You can't really be on a location. "I'm on Paris". How could you possibly be on top of an entire city? It makes no sense. So, use "on" when you are referring to physically being on top of an object.

*NOTE: "on" has many meanings in english. It can mean to power something up "turn on the light" or be a part of some idiom "I'm on top of it" (meaning I will go do and complete a task)

So there is a little bit of logic behind English. Not a lot, but a little. :)

there are some rules to it.

start at the top of the corresponding list and choose the first one that matches the situation.

LOCATION:

the location is some form of public transport: "on"
"on a train", "on a bus", "on a plane", etc...

the location is a surface (ground / wall / planet): "on"
"on the floor", "on Mars", "on the Moon", "on the wall", etc...

the location is a place that you spend a lot of time at, and are very familiar with as a result (work / school): "at"
"at school", "at [name of company I work for]", "at my house", etc...

the event is outside the location (or the location is outside): "at"
"at an open air concert", "at the train station" (event takes place just outside it), "at a meeting" (in another town / country), etc...

the location is a vehicle: "in"
"in a car", "in a taxi", "in a van", etc...

the location is inside and nearby the speaker (within 1km~ish): "in"
"in a meeting" (in the same building), "in a restaurant", "in a cupboard", etc...

pick either "in" or "at". It doesn't matter.


TIME:

a date or time based on something else: "at" / "when"
"at the end of the week", "at the start of the film", "at the moment X happened", "when X, [event]", ...

a specific time: "at"
"at 3pm today", "at 7:30", ...

a specific day (or a recurring day): "on"
"on the 15th of July", "on Tuesday", "on Mondays", ...

a specific month: "in"
"in February", etc...

a relative date or time (now + X): "in"
"in 5 hours", "in 2 days time", "in a minute", "in two and a half years" ...

a time period: "in" / "for" / "during"
"in the next 2 hours", "for most of the past year", "during summer vacation", ...