Meaning of verb + とも限らない


In an anime there is this exchange:

> だが無理はするな。お前は紅椿{あかつばき}での実戦経験は皆無だ。突然何かしらの問題が出る **とも限らない**
>
> 分かりました

I know that [とは限らない](https://japanesetest4you.com/flashcard/learn-
jlpt-n3-grammar-%E3%81%A8%E3%81%AF%E3%81%8B%E3%81%8E%E3%82%89%E3%81%AA%E3%81%84-towa-
kagiranai/) means "not necessarily", and from
[here](https://japanese.stackexchange.com/questions/55266/what-is-the-
difference-
between-%E3%81%A8%E3%81%AF%E9%99%90%E3%82%89%E3%81%AA%E3%81%84-and-%E3%81%A8%E3%82%82%E9%99%90%E3%82%89%E3%81%AA%E3%81%84)
I think とも限らない has the same meaning, beside being milder and indirect. Looking
around, I found that [ないとも限らない](https://japanesetest4you.com/flashcard/learn-
jlpt-n1-grammar-%E3%81%AA%E3%81%84%E3%81%A8%E3%82%82%E3%81%8B%E3%81%8E%E3%82%89%E3%81%AA%E3%81%84-nai-
tomo-kagiranai/) means "might", which fits with the idea of とも限らない meaning
"not necessarily" (ないとも限らない as "might", minus ない, gives "might not").

All of this seem coherent with the idea if とも限らない meaning "not necessarily",
but then I read the quoted exchange, and I'm not sure what it should mean:

> But don't push it. You don't have any real experience with Akatsubaki. Not
> necessarily any issue could arise all of a sudden

Which sounds odd to me: as a warning, I would expect something like "Any issue
could arise all of a sudden", which stresses the danger of such issue
happening.

I think that "might" and "might not" are not so far, as meaning, since
something that _might_ happen could also not happen, and using "might" just
stress the possibility it does happen; but I'm not sure if there is something
else.

Is this all that's happening, a simple stress on the fact that issue could not
arise (but they could, nevertheless)? Or am I missing something?




I have not been able to find any conclusive evidence to suggest one way or the
other, but I personally feel it is a misuse, or to be precise, a mix-up of two
similar constructs, namely `[V ない-stem]-ないとは／も限らない` and `[interrogative] [V
dictionary form]-とも限らない`.

This [page](https://nihongonosensei.net/?p=20639) specifically mentions the
latter usage with examples, as follows.

> 「いつ死ぬとも限らない（不知何时死）」等のように、「いつ」「どこ」などの疑問詞が来ると動辞形でも接続可能な場合もあります。例（７）（８）。
>
> （７）災害はいつ襲ってくるとも限らない。  
>  （灾害说不定什么时候就会来。）
>
> （８）首都圏ではいつ巨大な地震が起こるとも限らないと言われている。  
>  （据说首都圈随时都有可能发生大地震。）

One user on
[chiebukuro](https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q1478120909),
whose answer was not chosen as best, goes further to claim only いつ津波が襲って
**くる** とも限らない is grammatical and いつ津波が襲って **こない** とも限らない is not, contradicting
the best answer.

If these are accurate, the question is whether 何かしらの in your sentence
qualifies as an interrogative.

> 突然 **何かしらの** 問題が出るとも限らない。

I don’t think it does because it just means “some” and is not asking “what.”

We might get a grammatical sentence by replacing 何かしら with 何, or by adding いつ.

> 突然 **何の** 問題が出るとも限らない。
>
> **いつ** 突然何かしらの問題が出るとも限らない。

I am not very sure, though.




The both `出るとも限らない` / `出ないとも限らない` sounds the same to me(Japanese native) in
this context.

I suppose that this is because it implicitly contains bipolar conclusions.
i.e. `出るとも出ないとも限らない` (`We can't say either "it happens" or "it doesn't
happen"`)  
The particle 「 **も** 」 basically has meanings like `too`, `also`, `both`.
Coupled with the negation `限らない` it negates the both conclusions, `happen` and
`not happen`.

However, we would never use 出ると **は** 限らない in this context whereas `出ないとは限らない`
is possible.  
I suppose that this is because in many cases the particle 「 **は** 」 contains a
meaning like `Against your expectation`, `You may not know`. (Note that there
are exceptions)

> 出ると **は** 限らない  
>  I think you think it happens, but it's not necessarily so

> 出ないと **は** 限らない  
>  I think you think it doesn't happen, but it's not necessarily so

