When to use Dono or Nan?

Question

I am learning Japanese using "learn Japanese in the car". It has the following sentences:

Which seat is it? / Dono seki desu ka. 

Which train car is it? / Nan gosha desu ka.

Why does one use Dono and the other use Nan. What is the rule to know when to use each one?

Answer 1

席{せき} is a good example. Please look at examples as follows.

A. どの席{せき}ですか。
B. 何{なん}席{せき}ですか。
C. 何{なに}席{せき}ですか。

All of these are grammatically, and each sentence is different question from the others.

A. どの席ですか。

You would say A when you don't know which seat it is.
どの is used when you want to know which of the three or more.
どちらの is used if you don't know which of the two.

B. なん席ですか。

I dare to write in hiragana, なん, to make clear the pronunciation, although people usually write it in Kanji, 何.
B means ''How many seats?''

なん is used when you speak about the number, order, or the amount of something.
The answer will be a word with the number, or the ordinal.
''席'' in this sentence is a counter suffix. なん is followed by a counter suffix, as ''なん号車{ごうしゃ}'', ''なん人{にん}'', ''なん枚{まい}'', ''なん回{かい}'', ''なんメートル'', ''なんか国{こく}'', ''なん歳{さい}'', ''なん年{ねん}'', ''なん月{がつ}'', etc.

However, 曜日{ようび} is also asked with なん.
So if you forgot whether it is Wednesday or Thursday, you would ask someone ''今日はなん曜日ですか。''.

C. なに席ですか。

Perhaps this usage of なに isn't listed in dictionaries.
You can use ''なに席'' when you want to know what kind of the seat.
You can use it for many aspects of kind, so you and someone you talk to have to know what you guys are speaking about.
C can be a question about various features.

指定席{していせき} reserved seats／自由席{じゆうせき} non-reserved seats
禁煙席{きんえんせき} non-smoking seats／喫煙席{きつえんせき} smoking-allowed seats
テーブル席 seats at the table in a restaurant／カウンター席 seats at the counter
These of ''○○席'' can be asked by using ''なに席''.

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My kindergarten had three classes, ばら{rose}組{ぐみ}, もも{peach}組,　ゆり{lily}組. If I asked my friend what class had you been in, I would say ''幼稚園{ようちえん}の時{とき}、なに組だった？'' .
While, my elementary school and high school had several classes too, they ware named as 1組{くみ}, 2組, 3組, 4組, then, I would ask ''なん組だった？'' to my friend.
Furthermore, the university I graduated from has a large, extensive campus, so tourists who visit there may wonder that ''なん学部あるんだろう'', ''How many faculties are there in this campus''.
When you say なに学部, it means what kind of faculty as ''あなたはなに学部の学生ですか。''