What is 「長い」 modifying in the sentence 「もう日本に来て長いんですか」?


_**NOTE** : The title of the post is regarding the most bugging part of the
sentence to me (長い), but my problem is with the sentence as a whole._

I came across a sentence in my grammar exercises book I can't quite
understand. I get the general meaning of the sentence, but I am unable to
identify what grammar is used here. The original passage is as follows (the
troubling sentence is in **bold** ):

> ［状況］リーは1っか月前に日本に来た。
>
> 日本人: リーさんは日本語が本当にお上手ですね。 **もう日本に来て長いんですか** 。

I would translate it as:

> Japanese person: Rii, you are really good at Japanese. Has it passed much
> time since you came to Japan? (not sure about the second sentence)

Assuming my translation is right, I would rather say something along the lines
of:

> 日本にきて **から** 長い **時間** が経ったんですか。

I can't figure out the function of もう and 長い alone, not modifying any noun.
Any thoughts on this?

よろしくお願いします。




> 「日本にきてから長い時間が経ったんですか。」

is almost as same as the original sentence :「 **もう** 日本に来て長いんですか。」.

This 「もう」 is "explicitly" intensifying 「長い(時間が経った)」 since the author is
surprised at proficiency of Rii's Japanese and they want to make sure how much
time has passed(estimating it should be/may be very long!).

Technically speaking, your sentence:「日本にきてから長い時間が経ったんですか。」may be implicitly
intensifying 「長い時間が経った」, but it is difficult to be known without context.

The definition of 「もう」 from
[大辞林](https://kotobank.jp/word/%E3%82%82%E3%81%86-644796)

> ① 時間や程度が、ある基準や節目を超える意を表す。もはや。 「 －あれから一年たつ」 「 －これ以上食べられない」

  * **もう** あれから一年たつ : _"It's been already one year passed since then."_

  * **もう** これ以上食べられない : _"I can't eat any more."_

Without 「もう」 can be the same as my translation. However, with「もう」it emphasizes
it has already been beyond some "standard/capacity".




> 「日本にきてから長い時間が経ったんですか。」

is almost as same as the original sentence :「 **もう** 日本に来て長いんですか。」.

This 「もう」 is "explicitly" intensifying 「長い(時間が経った)」 since the author is
surprised at proficiency of Rii's Japanese and they want to make sure how much
time has passed(estimating it should be/may be very long!).

Technically speaking, your sentence:「日本にきてから長い時間が経ったんですか。」may be implicitly
intensifying 「長い時間が経った」, but it is difficult to be known without context.

The definition of 「もう」 from
[大辞林](https://kotobank.jp/word/%E3%82%82%E3%81%86-644796)

> ① 時間や程度が、ある基準や節目を超える意を表す。もはや。 「 －あれから一年たつ」 「 －これ以上食べられない」

  * **もう** あれから一年たつ : _"It's been already one year passed since then."_

  * **もう** これ以上食べられない : _"I can't eat any more."_

Without 「もう」 can be the same as my translation. However, with「もう」it emphasizes
it has already been beyond some "standard/capacity".

