～の？・～のですか・～んですか
Ask for an explanation
You’ll be able to ask someone to explain a situation rather than just confirm a fact.
もう帰るの？
mou kaeru no?
What do you think this sentence means?
You’re going home already?
Ask for the explanation behind a situation
Mei sees Ren packing up earlier than expected. Compared with the plain question もう帰る？, もう帰るの？ connects the question to what she has noticed and invites him to explain. の？ is casual; のですか and んですか are more polite.
どうして遅れたんですか。
doushite okureta n desu ka.
Why were you late?
Said after the listener arrives late; it asks them to explain the reason.
After verbs and い-adjectives
Use the plain form before の？, のですか, or んですか.
旅行に行くの？
ryokou ni iku no?
Are you going on a trip?
Asked after seeing someone packing bags or wheeling a suitcase.
こんな時間に何をしているんですか。
konna jikan ni nani o shite iru n desu ka.
What are you doing at this hour?
The unusual time prompts the speaker to ask what is happening.
どうしてそんなに高いんですか。
doushite sonna ni takai n desu ka.
Why is it so expensive?
The speaker has noticed the unusually high price and asks for the reason.
After nouns and な-adjectives
Use な before these explanatory question endings. In speech, な + んですか contracts naturally to なんですか.
制服を着ていますね。学生なんですか。
seifuku o kite imasu ne. gakusei nan desu ka.
You’re wearing a school uniform. Are you a student?
The uniform leads the speaker to wonder whether being a student explains it.
今日は会社に行きませんね。休みなんですか。
kyou wa kaisha ni ikimasen ne. yasumi nan desu ka.
You’re not going to the office today. Is it your day off?
Not going to the office is the clue; the speaker asks whether a day off explains it.
今日はどうしてこの辺が静かなんですか。
kyou wa doushite kono hen ga shizuka nan desu ka.
Why is this area so quiet today?
The unexpected quiet is already noticeable, so the speaker asks for its cause.
～ますか vs ～んですか
A plain polite question asks for a fact or plan. んですか connects the question to a situation you have noticed and invites the listener to give the background. After a verb, use its plain form before んですか.
Checking the plan
もう帰りますか。
mou kaerimasu ka.
Will you go home now?
Simply asks about the listener’s plan.
Asking about the situation
もう帰るんですか。
mou kaeru n desu ka.
You’re going home already?
Said after noticing the listener pack up early; it invites the background or reason.
もう帰るの。
mou kaeru no.
Are you going home already?
今日は学校に行かないの。
kyou wa gakkou ni ikanai no.
Aren't you going to school today?
どうして窓を開けているんですか。
doushite mado o akete iru n desu ka.
Why do you have the window open?
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