Differences between なぜ, なんで and どうして when the method is not relevant


I'm reading a book that got me thinking about the difference between なぜ, なんで
and どうして; as context, the speaking character (ガラザイア) is asking another
character (ギルロア) why he killed ルイーゼ様. The second character was close to ルイーゼ様
and her brother (レメディオス), and all the rebellion trusted him; I don't think
it's relevant, but while the speaking character is convinced the other killed
ルイーゼ様, it's never said so, and it could well be he didn't.

The narrator is a third character, which is secretely listening to the
conversation. This is the exchange that got me thinking:

> 『そうだ。シュトレーリッツ会戦で、貴様がルイーゼ様を裏切り、心臓を抉{えぐ}り取{と}った。汚{きたな}い手でな』
>
> [...]
>
> 『 **なぜ** 貴様は、ルイーゼ様を殺した？』
>
> [...]
>
> 『ルイーゼ様とレメディオス様は、本当に仲の良{い}い姉弟{きょうだい}だった。反乱軍は二人を中心に結束していた。だが、貴様が―』
>
> [...]
>
> 『すべてをぶち壊した』
>
> ギルロアの返答はない。
>
> 『なんとか言え』
>
> 怒りを押し殺したようなガラザイアの声だけが聞こえる。だが、ギルロアは何も言わない。
>
> 『くっ…… **なんで、どうして** ……』

Not sure if it's relevant, the speaking character is growing increasily
frustrated and angry.

I found [this](https://japanese.stackexchange.com/questions/2673/whats-the-
difference-
between-%E3%81%AA%E3%81%9C-%E3%81%A9%E3%81%86%E3%81%97%E3%81%A6-and-%E3%81%AA%E3%82%93%E3%81%A7-when-
meaning-why) answer explaining that while なぜ just asks for a cause, どうして and
なんで also asks for method; but in this case I really feel like the method is
completely irrelevant, both because she already said it in the first quoted
sentence, and because really it doesn't seem to matter _how_ he betrayed her,
but just the fact he did.

So, I was wondering what's the meaning and/or nuances of asking both なんで and
どうして (and, at the beginning, なぜ) in this case.




I think you get the meanings right. Simply put, なぜ is always _why_ and the
other two mean sometimes simple _why_ and sometimes asking for method (so they
are ambiguous to some extent).

When asking for a method, なんで is considered as 何+で=with what. As such, it can
be pronounced なにで which unambiguously asks for a method (i.e., なにで cannot mean
simple _why_ ).

どうして in the method-asking sense should be another form of どうやって, which I think
is more common. (In most cases, I would understand どうして as _why_ rather than
asking for method).

* * *

As a side note, my impression is that どうして and なんで for _why_ are more
colloquial, perhaps more common in casual speech. なぜ sounds formal or mature
(or kind of pressing), but it may depend. (I cannot imagine a child using なぜ
to parents).

The formal nature of なぜ may at least partially explain the usage in the
question: なぜ for the first enquiry, then どうして/なんで for talking to himself(?).
Use of two different words (instead of どうして、どうして or なんで、なんで) is a matter of
variation.




I think you get the meanings right. Simply put, なぜ is always _why_ and the
other two mean sometimes simple _why_ and sometimes asking for method (so they
are ambiguous to some extent).

When asking for a method, なんで is considered as 何+で=with what. As such, it can
be pronounced なにで which unambiguously asks for a method (i.e., なにで cannot mean
simple _why_ ).

どうして in the method-asking sense should be another form of どうやって, which I think
is more common. (In most cases, I would understand どうして as _why_ rather than
asking for method).

* * *

As a side note, my impression is that どうして and なんで for _why_ are more
colloquial, perhaps more common in casual speech. なぜ sounds formal or mature
(or kind of pressing), but it may depend. (I cannot imagine a child using なぜ
to parents).

The formal nature of なぜ may at least partially explain the usage in the
question: なぜ for the first enquiry, then どうして/なんで for talking to himself(?).
Use of two different words (instead of どうして、どうして or なんで、なんで) is a matter of
variation.

