"...sleep on..." vs "...sleep in..."

1- You sleep on a queen-sized bed.

2- You sleep in a queen-sized bed.

3- You sleep in a pajama. -- No.

4- You sleep in your pajamas.

Only '3' is wrong.

CJ

Why is 2 and 4 correct?

2- How is it okay to sleep 'in' a bed. A bed is more like a flat surface than a room.

4- Isn't pajamas more than one?

nerdikarpHow is it okay to sleep 'in' a bed.

Of the two prepositions 'in' and 'on', 'in' is more common with 'bed'. When you have the sheets and blankets over you, you feel that you are "in" something, so you are "in bed". But when you lie on top of the sheets and blankets, you are "on the bed".

nerdikarp4- Isn't pajamas mor

"4- Isn't pajamas more than one?"

Compare "trousers". "Pajama" or "pyjama" is not a noun, it's an adjective: Where are my pyjama trousers?

"2- How is it okay to sleep 'in' a bed. A bed is more like a flat surface than a room."

Read carefully CJ's explanation; when you sleep in a sleeping bag you are in it not on it. The same, you are in bed when you're covered with a blanket/sheet/quilt.

Anonymous"Pajama" or "pyjama" is not a noun, it's an adjective: Where are my pyjama trousers?

FYI. The most current terminology for this situation is that pyjama remains a noun; it doesn't become an adjective. It's a "modifying noun" rather than an "adjective".

If you still want to call it an adjective, in the sense of 'a noun that acts as an