Ask a yes-no question that leans toward a negative guess: 不 or 沒 negates the verb, 嗎 closes it, and the speaker checks a hunch drawn from what they see.
Ask a yes-no question that leans toward a negative guess
框 · Frame
[subj] 不/沒 [verb/state] 嗎？
觸 · Trigger
You have seen something and suspect a negative is true, and you want it confirmed.
序 · The move
1Name the negative you suspect from the evidence (not feeling well / no keys on hand).Are you leaning toward a no, not asking with an open mind? An open question with no lean is plain 嗎 or A-not-A.
2Pick the negator: 不 for a state, will, or quality; 沒 for possession, existence, or a finished act.State or quality → 不 (不舒服). Possession or past act → 沒 (沒帶). Wrong negator breaks the question.
3Set the negator before the verb and close with 嗎？Does 嗎 hang at the tail, turning the negative guess into a yes-or-no?
例 · Examples
1你今天怎麼那麼早就回家了，你不舒服not feeling well (不 bars the state)嗎closes each into a yes-no question？你怎麼站在外面，你沒帶didn't bring (沒 bars the finished act)鑰匙嗎？
You came home so early today — aren't you feeling well? Why are you standing outside — didn't you bring your keys?
Plain 嗎 asks an open yes-no with no lean (你舒服嗎？ are you well?). 不/沒…嗎 carries a negator inside, so the speaker is already leaning toward a no and asking to confirm it (你不舒服嗎？ aren't you well?).
The negator splits by job: 不 bars a state, will, or quality (不舒服, 不去); 沒 bars possession, existence, or a finished act (沒帶, 沒錢). Same lean, different thing being denied.
你沒舒服嗎？ → 你不舒服嗎？ (舒服 is a state, so the negator is 不, not 沒)
你不帶鑰匙嗎？ → 你沒帶鑰匙嗎？ (a finished act takes 沒; 不帶 would mean a refusal to bring)
你不舒服不舒服嗎？ → 你不舒服嗎？ (the 嗎 question carries one negator; do not stack A-not-A inside it)
English negative questions (aren't you well? didn't you bring it?) use one 'not' for every case, so learners reach for a single negator where Mandarin splits 不 (state/will/quality) from 沒 (possession/existence/completion).