For example, when you're talking to someone and asking them why they're still awake when it's really late.
你怎麼還沒睡覺?
你怎麼還不睡覺?
I know both convey some meaning of asking the other person why they aren't sleeping yet and I've seen both used in conversation before. I'm wondering what's the difference between the two? Thanks in advance.
For practical purposes, there are interchangeable.
However, for certain specific situations, one may be preferred, only preferred, not mandatory over the other.
还没 is used when it is a bare, neutral statement / comment on someone not asleep yet.
还不 is used when it is questioning / accusative of why someone is not asleep yet when ought to be.
So, you have:-
很晚了，你还没睡
明天去上学你还不睡
However, no one will say you are absolutely wrong if used interchangeably.
你怎麼還沒睡覺? For some outside reason the person is not able to go to sleep on time. Like too much homework to do. 你怎麼還不睡覺? The person is not going to bed for his own reason. For example he is playing games and does not want to go sleep right now.
The tone of 还不 is a little stronger. You can imagine that 没 is '没有' and 不 is '否定 sth.'
'没有'睡觉 is more implicit;
'否定'睡觉 is more stronger.
So where you can usually use 还不 , you can use 还没 to replace. But not the other way around sometimes it's a little not polite.
The question can be simplified to what is the difference between [不 + verb] and [没 + verb]
不睡 = not sleep (actively refuse to sleep)
不吃 = not eat (actively refuse to eat)
没睡 = didn't sleep/ haven't slept (for whatever reason)
没吃 = didn't eat/ haven't eaten (for whatever reason)
没 can be short for 没有(without) e.g. 沒錢 = 沒有錢(without money/ no money)
不 can only be an adverb for a verb
深夜了还不睡 = still do not sleep late in the night (actively refuse to sleep)
深夜了还沒睡 = still haven't slept late in the night (for whatever reason - including unwilling, unable, and forget to. The reason is not important, 还沒睡 is just stating an observable fact that someone is still awake)
你怎麼還沒睡覺? Why haven't(沒) you slept yet?
你怎麼還不睡覺? Why are you not(不) to sleep yet?
