prepositions

Hello, please I need your help. I have some doubts about the use of the prepositions ON/IN/AT and I want to know the accurate choice for these sentences:

We want to start the meeting on time/in time, so please don t be late.
Where is the car waiting? At/on the traffic lights.
The leaves on/at that tree are a beautiful color.
He spends most of the day sitting at/on the window and looking outside.
I like that picture hanging on wall in/at the kitchen.

Thanks a lot.

[Casiopea]

In general, 'on' is short for on top of a surface, 'in' is short for inside of a structure, and 'at' means a point in space or time.

1. We want to start the meeting on time, so please don t be late.
==> Time = numbers; numbers are on the surface of a clock's face. 'on time' is an idiom meaning punctual, not late.

2. Where is the car waiting? Atthe traffic lights.
==> Location = a point in space; the car is not sitting on top of the traffic lights.

3. The leaves onthat tree are a beautiful color.
==> The leaves are located on the branches of the tree.

4. He spends most of the day sitting atthe window and looking outside.
==> Location = a point in space; he is not sitting on top of the window.

5. I like that picture hanging on the wall inthe kitchen.
==> The kitchen is a 3 dimentional space. It is a room, a structure. It has an inside, so use 'in(side)' the kitchen.

All the best,

[RonBee]

Excellent explanation, Cas!

:D

Casiopea, thanks for your reply. I still have some doubts about the use of these prepositions.
For example, when do I use IN or AT when I speak about a University or a restaurant if both of them are a trhee dimesional structures and I could be inside?

She goes to classes at the university OR She goes to classes in the university
We stayed in a very nice hotel OR We stayed at a very nice hotel

Also,
I last saw Ann at/on Dave s wedding
I saw him at/on your birthday.
I think I must use ON but someones do not.

Thanks again.

[MikeNewYork]

Originally Posted by Elsa

Casiopea, thanks for your reply. I still have some doubts about the use of these prepositions.
For example, when do I use IN or AT when I speak about a University or a restaurant if both of them are a trhee dimesional structures and I could be inside?

She goes to classes at the university OR She goes to classes in the university
We stayed in a very nice hotel OR We stayed at a very nice hotel

Also,
I last saw Ann at/on Dave s wedding
I saw him at/on your birthday.
I think I must use ON but someones do not.

Thanks again.

Cas's rules were excellent and they cover most uses of these prepositions. Some uses are idiomatic and they can be strange.

One normally takes classes "at" a university. One studies at a university. This is because a university is not usually a single building. One can take classes in Palmer Hall (a university building) or study in the Smith Library.

I saw Ann at Dave's wedding (a party, a celebration).
I saw Ann on Dave's wedding day (a day).

I saw him on your birthday (a day).
I saw him at your birthday party (a party).

A tough one is a destination that is also a position or an enclosure.

I met her on the corner (a position).
I met her at the corner (a destination).

I met her at the restaurant. (a destination).
I met her in the reatuarant. (a building)

Thank you Mike! It s an excellent explanation! I think that with your reply and Casiopea s I have resolved my doubts. :D

[MikeNewYork]

Originally Posted by Elsa

Thank you Mike! It s an excellent explanation! I think that with your reply and Casiopea s I have resolved my doubts. :D

You're very welcome. :)