When does it make sense to use 「〜でない。」？ , which isn't particularly common as a sentence-ender, does occasionally get used. I get the feeling it is pretty curt; I often see it with or or , etc. However, I don't have a good understanding of when it makes sense to choose it over . Is it when you're trying to be more declarative/emotionless as opposed to emphatic/opinionated?

Basically it's a matter of grammar rather than nuance.

As you may know, in is (semantically almost bleached out but still functioning) topic marker in the theme-rheme structure of Japanese. In other words, it delimits theme and rheme parts of a clause. And one clause may only contain up to one theme and rheme respectively.

Then, what happens if you use two at once in a sentence?

>

You may feel a sense of dissonance because:

* [ [ ] ]
* [ [ ] ]



It has two possible breakdowns so you can't decide which is the main theme of the sentence.
(Note that some people don't feel anything wrong because they conceive to be a monolithic chunk.)
Thus carefully written sentences often omit the in in order to avoid confusing readers by any chance.

* ****
* ****



Of course, in the colloquial language, has taken over them so that the difference between and is neutralized.