What's the grammar structure of ここしかない in this sentence?


> 安全な所はここしかない

I think there may be 2 explanations of しか in this sentence:  

  * しか replaced the case particle が. But if we transform it back and change the negation to the positive form: 安全な所はここだけ **が** ある.  
I added the だけ to imply the meaning of "only". But this sentence sounds a
little unnatural, so I don't think it's the correct explanation.

  * しかない is transformed form である: 安全な所はここだけである.   
It sounds natural and has a similar meaning to the original sentence. But to
use しか for である, shouldn't it be 安全な所はここ **で** しかない?

These 2 explanations correspond to ここがある and ここである respectively. But which is
correct? The question maybe equal to this: Is the ない in the original sentence
非存在を表す形容詞 or 否定の助動詞?




First, Xでしかない and Xしかない have different meanings.

### Xでしかない = nothing other than X; nothing more than X; merely X

  * それは夢である。That's a dream.  
それは夢でしかない。That's nothing more than a dream.  
それは夢しかない。×

  * 彼は学生である。He is a student.  
彼は学生でしかない。He is merely a student.  
彼は学生しかない。×

### Xしかない = X is the only option; there is nothing but X; there is only X

  * 行くなら候補は日曜日である。If we go, the option is Sunday.  
行くなら候補は日曜日でしかない。If we go, the option is nothing but Sunday.  
行くなら候補は日曜日がある。If we go, there is an option of (going on) Sunday.  
行くなら候補は日曜日しかない。If we go, the only option is Sunday.

  * 正しい答えはAである。The correct answer is A.  
正しい答えはAでしかない。(You may be thinking B is correct but) the correct answer can be
nothing but A.  
正しい答えはAがある。(You may be thinking there is no answer but) there _is_ a correct
answer, A.  
正しい答えはAしかない。(You may be thinking there are multiple correct answers but) the
only correct answer is A.

  * 安全な場所はここである。The safe place is here.  
安全な場所はここでしかない。The safe place is here (and not somewhere else).  
(The focus is "which place is considered safe?")  
安全な場所はここがある。As for safe places, we do have this place.  
安全な場所はここしかない。The only safe place is here.  
(The focus is "how many safe places are there?")

  * 10円玉がある。There are 10-yen coins.  
10円玉しかない。There are only 10-yen coins.

Semantically, the Xしかない pattern denies the existence of other options, so it's
ない for 存在, and that's why で must not be used.

But that does not mean we commonly say 候補は日曜日がある, 安全な場所はここがある and so on. These
are natural only when you need to strongly emphasize the existence of X, as
shown above. Normally, である can be seen as the natural "opposite" of those しかない
sentences.

Also note that しかない is over 100 times more common than だけがある. There are some
rare contexts where だけがある could sound natural, but let's not use it as the
base of our discussion here.




First, Xでしかない and Xしかない have different meanings.

### Xでしかない = nothing other than X; nothing more than X; merely X

  * それは夢である。That's a dream.  
それは夢でしかない。That's nothing more than a dream.  
それは夢しかない。×

  * 彼は学生である。He is a student.  
彼は学生でしかない。He is merely a student.  
彼は学生しかない。×

### Xしかない = X is the only option; there is nothing but X; there is only X

  * 行くなら候補は日曜日である。If we go, the option is Sunday.  
行くなら候補は日曜日でしかない。If we go, the option is nothing but Sunday.  
行くなら候補は日曜日がある。If we go, there is an option of (going on) Sunday.  
行くなら候補は日曜日しかない。If we go, the only option is Sunday.

  * 正しい答えはAである。The correct answer is A.  
正しい答えはAでしかない。(You may be thinking B is correct but) the correct answer can be
nothing but A.  
正しい答えはAがある。(You may be thinking there is no answer but) there _is_ a correct
answer, A.  
正しい答えはAしかない。(You may be thinking there are multiple correct answers but) the
only correct answer is A.

  * 安全な場所はここである。The safe place is here.  
安全な場所はここでしかない。The safe place is here (and not somewhere else).  
(The focus is "which place is considered safe?")  
安全な場所はここがある。As for safe places, we do have this place.  
安全な場所はここしかない。The only safe place is here.  
(The focus is "how many safe places are there?")

  * 10円玉がある。There are 10-yen coins.  
10円玉しかない。There are only 10-yen coins.

Semantically, the Xしかない pattern denies the existence of other options, so it's
ない for 存在, and that's why で must not be used.

But that does not mean we commonly say 候補は日曜日がある, 安全な場所はここがある and so on. These
are natural only when you need to strongly emphasize the existence of X, as
shown above. Normally, である can be seen as the natural "opposite" of those しかない
sentences.

Also note that しかない is over 100 times more common than だけがある. There are some
rare contexts where だけがある could sound natural, but let's not use it as the
base of our discussion here.

