I heard many times ‘I write on paper and sign on paper’ but also heard ‘commented in your post’. I read somewhere in is used with emails and letters but many times I read ‘on’ with letters.
Paper is simillar to letter. I have read ‘sign on paper’ why it is not ‘sign in paper? I want to know how to know that when to use “in” and when to use “on”. Please help.
‘on your letter’ is not correct unless you mean:
‘I spilled coffee on your letter/book.’
The correct forms are:
- ‘IN your letter/post/email/book you mentioned/said/wrote that…’
- ‘A lot of people have commented ON this post.’
ON refers to the surface of things:
- There’s something written on the wall (on the surface of the wall)
- There is a cat on the desk (on the surface)
So yes, you can write something ON PAPER, but the WORDS of a letter/email/ book/comment have no surface so you don’t normally use the preposition ON together with these words.
Unless your cat is sitting ON your book which means you can’t open it, because the cat is on the surface/top of your book.
IN means CONTAINED. If something is IN another thing, it is CONTAINED
- In the book there are 3 main characters. (the story contains these characters)
If these concepts are not helpful or clear to you, just try to memorize the correct examples. It’s usually more useful to learn some examples than trying to memorize some difficult rules…
Regarding COMMENT ON something:
She commented ON my post.
IN her comment she said that…
I hope these help!
