This looks like a duplicate but it's not. Here is the 2013 question:
In farms or on farms? The OP only wanted to know which sentence was grammatically correct.
- They live the quiet life on farms
- They live the quiet life in farms
Instead I would like to know why we say “on a farm” and not “in a farm”
I was teaching English to a small group of Italian kids this morning, and we were playing "Guess which animal am I". While it was easy enough to get them to say
Do you live in a jungle?
Do you live in a house?
Do you live in the water?
Do you live in a tree?
Do you live in a garden?
For one kid the question
Do you live on a farm?
proved to be quite a battle, so I pretended to be deaf when he asked Do you live in a farm? until he got the phrase exactly right.
However, it would be neat if I could provide an easy explanation or mnemonic for these kids to remember, apart from me acting decrepit and deaf again next week. Any ideas?
Please, no comments on my being pedantic and fiscal, I know it's not the end of civilization as we know it, if a learner says I live in a farm but the preposition on is used in this case, and parents pay me to teach their kids!
Best Answer
I haven't done any research in vetted sources for this answer, but here's how I approach it at low levels with my students. The following is a rule of thumb.
We use in to denote being within spaces that we perceive as being three-dimensional. Jungles, houses, trees and water are things which when we're in them surround us on all sides in a three dimensional way. Notice that in the Original Poster's examples, this applies to animals that live in the water. It isn't really true of humans - who might live on the water.
We also use in to describe being confined in a delineated two dimension area. For example, in a cell in your database or in a field or in London, in England and so forth. This, I think, is the reason for in a garden in the Original Poster's examples.
We use on to denote being on a surface or plane of some description:
This is especially true when we think of this surface or plane as extending out indefinitely or over some great distance:
It seems that in English, we view farms, ranches and the like as planes that extend outwards as opposed to as clearly defined two dimensional areas. (Compare with a garden or a field). Notice that with some words it just depends how we're thinking about them that determines whether we use in or on, for example with the word water. Also, sometimes we can just choose whether to use in or on because we can think about something as being either a delineated area or a plane: