Vague subject of sentence


どうして田中が好きなんですか

From what i understand, the sentence above doesn't have any subject, so
depending on the context, it can be both _Why do I like Tanaka?_ or _Why do
you like Tanaka?_

Is this correct ?




In this case, it can be any one else, but not yourself.

Making a question sentence whose subject is the first person is highly
restricted, because ordinary Japanese question expects the speaker doesn't
have firsthand knowledge about what's asked. It'd thus sound very, very weird
if you ask something about yourself that you ought to feel or know inside you.
To avoid this, you can add だろう (or polite form でしょう) to show the existence of
introspection.

> どうして田中が好きなの？  
>  _Why [ × do I / do you / does somebody ] like Tanaka?_
>
> (cf. どうして田中が好きなのか _Why [ I / you / somebody ] like(s) Tanaka_ )  
>  (casual plain form + か can't form a valid wh-question, but only indirect
> question, unless in the construction `～は + wh + か`)
>
> どうして田中が好きなんだろう（か）？  
>  _Why [ do I / do you / does sb. ] like Tanaka (, I wonder)?_
>
> どうして田中が好きなんです（か）？  
>  _Why [ × do I / do you / does sb. ] like Tanaka?_ (polite)
>
> どうして田中が好きなんでしょう（か）？  
>  _Why [ do I / do you / does sb. ] like Tanaka (, I wonder)?_ (polite)

Maybe you've heard the questioner in TV quiz program sets problems to the
panel using でしょう ending. It's a good example that suggests the questioner is
asking them knowing the answer.

Of course, in following cases you can dispense with だろう:

> どうして田中なんか好きになっちゃったの？ _Why (at all) did I fall in love with a guy like
> Tanaka?_  
>  (what is beyond your control or expectation)
>
> どうしたら健康で長生きできるのですか？ _How can I live a long, healthy life?_  
>  (what is out of your knowledge)
>
> ここはどこですか？私は誰ですか？ _Where am I? Who am I?_  
>  (...or you've lost it)




(As l'électeur pointed out, the grammatical subject of 田中が好き is 田中 ([here's
why](https://japanese.stackexchange.com/a/17876/5010)). But I'm assuming
you're concerned about the person who likes 田中.)

どうして田中が好きなんですか can mean "Why do **you** like Tanaka" (second person) or "Why
does **he/she** like Tanaka" (third person), depending on the context.

But it almost never means "Why do **I** like Tanaka?" (i.e., "I know I like
Tanaka, but I wonder why I like him.")

If "I" (as the first person) don't know why "I" like Tanaka, "I" have to say:

>   * どうして田中が好きなんだろう？
>   * どうして田中が好きなんだろうか？
>

Here, this だろう is an "I-think / I-wonder" marker (I don't know how to call
this properly).

～ですか? can be used only when the speaker explicitly requests the answer,
believing the listener knows the answer. Saying どうして田中が好きなんですか to yourself is
almost like saying "Tell me why do I like Tanaka!" to yourself!

Likewise, どこに行くんですか? can mean "Where will you/we/he/she/they go?", but it
never means "Where will **I** go?". When you want to ask yourself such a
thing, you have to say "どこに行こう?" using the volitional marker う/よう.

