Position words: In and On - when to use which?

Here's a simple

rule of thumb for "on": Anything can be on something flat.

examples:
I hung a picture on the wall. (walls are flat and vertical)
I was on the field ( the ground is generally flat)
She stood on a chair. (a chair is usually flat)
He saw it on TV (TV screens are flat)

Use In when there is something to be "inside".

examples:
I hung the picture in the middle of the wall. (the boundaries are the edges of the wall)
I was in the field (the field is bounded by its edges)
She was in the dining room (a room is bound by walls)
He saw the advert in the TV program (the program has a start and end, which are its boundaries).

Ask me your tricky "on or in" questions below 👇👇👇